BASH(1) BASH(1) NNAAMMEE bash - GNU Bourne-Again SHell SSYYNNOOPPSSIISS bbaasshh [options] [file] CCOOPPYYRRIIGGHHTT Bash is Copyright (C) 1989, 1991 by the Free Software Foundation, Inc. DDEESSCCRRIIPPTTIIOONN BBaasshh is an sshh-compatible command language interpreter that executes commands read from the standard input or from a file. BBaasshh also incorporates useful features from the _K_o_r_n and _C shells (kksshh and ccsshh). BBaasshh is ultimately intended to be a faithful implementa- tion of the IEEE Posix Shell and Tools specification (IEEE Working Group 1003.2). OOPPTTIIOONNSS In addition to the single-character shell options docu- mented in the description of the sseett builtin command, bbaasshh interprets the following flags when it is invoked: --cc _s_t_r_i_n_g If the --cc flag is present, then commands are read from _s_t_r_i_n_g. --ii If the --ii flag is present, the shell is _i_n_t_e_r_a_c_- _t_i_v_e. --ss If the --ss flag is present, or if no arguments remain after option processing, then commands are read from the standard input. This option allows the positional parameters to be set when invoking an interactive shell. -- A single -- signals the end of options and dis- ables further option processing. Any arguments after the -- are treated as filenames and argu- ments. An argument of ---- is equivalent to an argument of --. BBaasshh also interprets a number of multi-character options. These options must appear on the command line before the single-character options to be recognized. --nnoorrcc Do not load the personal initialization file _~_/_._b_a_s_h_r_c if the shell is interactive. This is the default if the shell is invoked as sshh. --nnoopprrooffiillee Do not read either the system-wide startup file _/_e_t_c_/_p_r_o_f_i_l_e or any of the personal initializa- tion files _~_/_._b_a_s_h___p_r_o_f_i_l_e, _~_/_._b_a_s_h___l_o_g_i_n, or _~_/_._p_r_o_f_i_l_e. By default, bbaasshh normally reads these files when it is invoked as a login shell. GNU 1993 August 9 1 BASH(1) BASH(1) --rrccffiillee _f_i_l_e Execute commands from _f_i_l_e instead of the stan- dard personal initialization file _~_/_._b_a_s_h_r_c, if the shell is interactive. --vveerrssiioonn Show the version number of this instance of bbaasshh when starting. --qquuiieett Do not be verbose when starting up (do not show the shell version or any other information). --llooggiinn Make bbaasshh act as if it had been invoked as a login shell. --nnoobbrraacceeeexxppaannssiioonn Do not perform curly brace expansion (see BBrraaccee EExxppaannssiioonn below). --nnoolliinneeeeddiittiinngg Do not use the GNU _r_e_a_d_l_i_n_e library to read com- mand lines if interactive. --ppoossiixx Change the behavior of bash where the default operation differs from the 1003.2 standard to match the standard AARRGGUUMMEENNTTSS If arguments remain after option processing, and neither the --cc nor the --ss option has been supplied, the first argument is assumed to be the name of a file containing shell commands. If bbaasshh is invoked in this fashion, $$00 is set to the name of the file, and the positional parameters are set to the remaining arguments. BBaasshh reads and exe- cutes commands from this file, then exits. DDEEFFIINNIITTIIOONNSS bbllaannkk A space or tab. wwoorrdd A sequence of characters considered as a single unit by the shell. Also known as a ttookkeenn. nnaammee A _w_o_r_d consisting only of alphanumeric characters and underscores, and beginning with an alphabetic character or an underscore. Also referred to as an iiddeennttiiffiieerr. mmeettaacchhaarraacctteerr A character that, when unquoted, separates words. One of the following: || && ;; (( )) << >> <> <> ccoonnttrrooll ooppeerraattoorr A _t_o_k_e_n that performs a control function. It is one of the following symbols: |||| && &&&& ;; ;;;; (( )) || <> RREESSEERRVVEEDD WWOORRDDSS _R_e_s_e_r_v_e_d _w_o_r_d_s are words that have a special meaning to the shell. The following words are recognized as reserved when unquoted and either the first word of a simple com- mand (see SSHHEELLLL GGRRAAMMMMAARR below) or the third word of a ccaassee or ffoorr command: !! ccaassee ddoo ddoonnee eelliiff eellssee eessaacc ffii ffoorr ffuunnccttiioonn iiff iinn tthheenn GNU 1993 August 9 2 BASH(1) BASH(1) uunnttiill wwhhiillee {{ }} SSHHEELLLL GGRRAAMMMMAARR SSiimmppllee CCoommmmaannddss A _s_i_m_p_l_e _c_o_m_m_a_n_d is a sequence of optional variable assignments followed by _b_l_a_n_k-separated words and redirec- tions, and terminated by a _c_o_n_t_r_o_l _o_p_e_r_a_t_o_r. The first word specifies the command to be executed. The remaining words are passed as arguments to the invoked command. The return value of a _s_i_m_p_l_e _c_o_m_m_a_n_d is its exit status, or 128+_n if the command is terminated by signal _n. PPiippeelliinneess A _p_i_p_e_l_i_n_e is a sequence of one or more commands separated by the character ||. The format for a pipeline is: [ ! ] _c_o_m_m_a_n_d [ || _c_o_m_m_a_n_d_2 ... ] The standard output of _c_o_m_m_a_n_d is connected to the stan- dard input of _c_o_m_m_a_n_d_2. This connection is performed before any redirections specified by the command (see RREEDDIIRREECCTTIIOONN below). If the reserved word !! precedes a pipeline, the exit sta- tus of that pipeline is the logical NOT of the exit status of the last command. Otherwise, the status of the pipeline is the exit status of the last command. The shell waits for all commands in the pipeline to terminate before returning a value. Each command in a pipeline is executed as a separate pro- cess (i.e., in a subshell). LLiissttss A _l_i_s_t is a sequence of one or more pipelines separated by one of the operators ;;, &&, &&&&, or ||||, and terminated by one of ;;, &&, or <>. Of these list operators, &&&& and |||| have equal precendence, followed by ;; and &&,, which have equal precedence. If a command is terminated by the control operator &&, the shell executes the command in the _b_a_c_k_g_r_o_u_n_d in a sub- shell. The shell does not wait for the command to finish, and the return status is 0. Commands separated by a ;; are executed sequentially; the shell waits for each command to terminate in turn. The return status is the exit status of the last command executed. The control operators &&&& and |||| denote AND lists and OR lists, respectively. An AND list has the form _c_o_m_m_a_n_d &&&& _c_o_m_m_a_n_d_2 GNU 1993 August 9 3 BASH(1) BASH(1) _c_o_m_m_a_n_d_2 is executed if, and only if, _c_o_m_m_a_n_d returns an exit status of zero. An OR list has the form _c_o_m_m_a_n_d |||| _c_o_m_m_a_n_d_2 _c_o_m_m_a_n_d_2 is executed if and only if _c_o_m_m_a_n_d returns a non- zero exit status. The return status of AND and OR lists is the exit status of the last command executed in the list. CCoommppoouunndd CCoommmmaannddss A _c_o_m_p_o_u_n_d _c_o_m_m_a_n_d is one of the following: (_l_i_s_t) _l_i_s_t is executed in a subshell. Variable assign- ments and builtin commands that affect the shell's environment do not remain in effect after the com- mand completes. The return status is the exit sta- tus of _l_i_s_t. { _l_i_s_t; } _l_i_s_t is simply executed in the current shell envi- ronment. This is known as a _g_r_o_u_p _c_o_m_m_a_n_d. The return status is the exit status of _l_i_s_t. ffoorr _n_a_m_e [ iinn _w_o_r_d; ] ddoo _l_i_s_t ; ddoonnee The list of words following iinn is expanded, gener- ating a list of items. The variable _n_a_m_e is set to each element of this list in turn, and _l_i_s_t is exe- cuted each time. If the iinn _w_o_r_d is omitted, the ffoorr command executes _l_i_s_t once for each positional parameter that is set (see PPAARRAAMMEETTEERRSS below). The exit status is the exit status of the last command, or zero if no commands were executed. ccaassee _w_o_r_d iinn [ _p_a_t_t_e_r_n [ || _p_a_t_t_e_r_n ] ... ) _l_i_s_t ;; ] ... eessaacc A ccaassee command first expands _w_o_r_d, and tries to match it against each _p_a_t_t_e_r_n in turn, using the same matching rules as for pathname expansion (see PPaatthhnnaammee EExxppaannssiioonn below). When a match is found, the corresponding _l_i_s_t is executed. After the first match, no subsequent matches are attempted. The exit status is zero if no patterns are matches. Otherwise, it is the exit status of the last com- mand executed in _l_i_s_t. iiff _l_i_s_t tthheenn _l_i_s_t [ eelliiff _l_i_s_t tthheenn _l_i_s_t ] ... [ eellssee _l_i_s_t ] ffii The iiff _l_i_s_t is executed. If its exit status is zero, the tthheenn _l_i_s_t is executed. Otherwise, each eelliiff _l_i_s_t is executed in turn, and if its exit GNU 1993 August 9 4 BASH(1) BASH(1) status is zero, the corresponding tthheenn _l_i_s_t is exe- cuted and the command completes. Otherwise, the eellssee _l_i_s_t is executed, if present. The exit status is the exit status of the last command executed, or zero if no condition tested true. wwhhiillee _l_i_s_t ddoo _l_i_s_t ddoonnee uunnttiill _l_i_s_t ddoo _l_i_s_t ddoonnee The wwhhiillee command continuously executes the ddoo _l_i_s_t as long as the last command in _l_i_s_t returns an exit status of zero. The uunnttiill command is identical to the wwhhiillee command, except that the test is negated; the ddoo _l_i_s_t is executed as long as the last command in _l_i_s_t returns a non-zero exit status. The exit status of the wwhhiillee and uunnttiill commands is the exit status of the last ddoo _l_i_s_t command executed, or zero if none was executed. [ ffuunnccttiioonn ] _n_a_m_e () { _l_i_s_t; } This defines a function named _n_a_m_e. The _b_o_d_y of the function is the _l_i_s_t of commands between { and }. This list is executed whenever _n_a_m_e is speci- fied as the name of a simple command. The exit status of a function is the exit status of the last command executed in the body. (See FFUUNNCCTTIIOONNSS below.) CCOOMMMMEENNTTSS In a non-interactive shell, or an interactive shell in which the --oo iinntteerraaccttiivvee--ccoommmmeennttss option to the sseett builtin is enabled, a word beginning with ## causes that word and all remaining characters on that line to be ignored. An interactive shell without the --oo iinntteerraacc-- ttiivvee--ccoommmmeennttss option enabled does not allow comments. QQUUOOTTIINNGG _Q_u_o_t_i_n_g is used to remove the special meaning of certain characters or words to the shell. Quoting can be used to disable special treatment for special characters, to pre- vent reserved words from being recognized as such, and to prevent parameter expansion. Each of the _m_e_t_a_c_h_a_r_a_c_t_e_r_s listed above under DDEEFFIINNIITTIIOONNSS has special meaning to the shell and must be quoted if they are to represent themselves. There are three quoting mechanisms: the _e_s_c_a_p_e _c_h_a_r_a_c_t_e_r, single quotes, and dou- ble quotes. A non-quoted backslash (\\) is the _e_s_c_a_p_e _c_h_a_r_a_c_t_e_r. It preserves the literal value of the next character that follows, with the exception of . If a \\ pair appears, and the backslash is not quoted, the \\ is treated as a line continuation (that is, it is effectively ignored). GNU 1993 August 9 5 BASH(1) BASH(1) Enclosing characters in single quotes preserves the lit- eral value of each character within the quotes. A single quote may not occur between single quotes, even when pre- ceded by a backslash. Enclosing characters in double quotes preserves the lit- eral value of all characters within the quotes, with the exception of $$, ``, and \\. The characters $$ and `` retain their special meaning within double quotes. The backslash retains its special meaning only when followed by one of the following characters: $$, ``, "", \\, or <>. A double quote may be quoted within double quotes by preced- ing it with a backslash. The special parameters ** and @@ have special meaning when in double quotes (see PPAARRAAMMEETTEERRSS below). PPAARRAAMMEETTEERRSS A _p_a_r_a_m_e_t_e_r is an entity that stores values, somewhat like a variable in a conventional programming language. It can be a _n_a_m_e, a number, or one of the special characters listed below under SSppeecciiaall PPaarraammeetteerrss. For the shell's purposes, a _v_a_r_i_a_b_l_e is a parameter denoted by a _n_a_m_e. A parameter is set if it has been assigned a value. The null string is a valid value. Once a variable is set, it may be unset only by using the uunnsseett builtin command (see SSHHEELLLL BBUUIILLTTIINN CCOOMMMMAANNDDSS below). A _v_a_r_i_a_b_l_e may be assigned to by a statement of the form _n_a_m_e=[_v_a_l_u_e] If _v_a_l_u_e is not given, the variable is assigned the null string. All _v_a_l_u_e_s undergo tilde expansion, parameter and variable expansion, command substitution, arithmetic expansion, and quote removal. If the variable has its --ii attribute set (see ddeeccllaarree below in SSHHEELLLL BBUUIILLTTIINN CCOOMM-- MMAANNDDSS) then _v_a_l_u_e is subject to arithmetic expansion even if the $[...] syntax does not appear. Word splitting is not performed, with the exception of ""$$@@"" as explained below under SSppeecciiaall PPaarraammeetteerrss. Pathname expansion is not performed. PPoossiittiioonnaall PPaarraammeetteerrss A _p_o_s_i_t_i_o_n_a_l _p_a_r_a_m_e_t_e_r is a parameter denoted by one or more digits, other than the single digit 0. Positional parameters are assigned from the shell's arguments when it is invoked, and may be reassigned using the sseett builtin command. Positional parameters may not be assigned to with assignment statements. The positional parameters are temporarily replaced when a shell function is executed (see FFUUNNCCTTIIOONNSS below). GNU 1993 August 9 6 BASH(1) BASH(1) When a positional parameter consisting of more than a sin- gle digit is expanded, it must be enclosed in braces (see EEXXPPAANNSSIIOONN below). SSppeecciiaall PPaarraammeetteerrss The shell treats several parameters specially. These parameters may only be referenced; assignment to them is not allowed. ** Expands to the positional parameters, starting from one. When the expansion occurs within double quotes, it expands to a single word with the value of each parameter separated by the first character of the IIFFSS special variable. That is, ``$$**'' is equivalent to ``$$11_c$$22_c......'', where _c is the first character of the value of the IIFFSS variable. If IIFFSS is null or unset, the parameters are separated by spaces. @@ Expands to the positional parameters, starting from one. When the expansion occurs within double quotes, each parameter expands as a separate word. That is, `` $$@@'' is equivalent to ``$$11'' ``$$22'' ... When there are no positional parameters, ``$$@@'' and $$@@ expand to nothing (i.e., they are removed). ## Expands to the number of positional parameters in decimal. ?? Expands to the status of the most recently executed foreground pipeline. -- Expands to the current option flags as specified upon invocation, by the sseett builtin command, or those set by the shell itself (such as the --ii flag). $$ Expands to the process ID of the shell. In a () subshell, it expands to the process ID of the cur- rent shell, not the subshell. !! Expands to the process ID of the most recently exe- cuted background (asynchronous) command. 00 Expands to the name of the shell or shell script. This is set at shell initialization. If bbaasshh is invoked with a file of commands, $$00 is set to the name of that file. Otherwise, it is set to the pathname used to invoke bbaasshh, as given by argument zero. __ Expands to the last argument to the previous com- mand, after expansion. Also set to the full path- name of each command executed and placed in the environment exported to that command. SShheellll VVaarriiaabblleess The following variables are set by the shell: PPPPIIDD The process ID of the shell's parent. PPWWDD The current working directory as set by the ccdd com- mand. OOLLDDPPWWDD The previous working directory as set by the ccdd GNU 1993 August 9 7 BASH(1) BASH(1) command. RREEPPLLYY Set to the line of input read by the rreeaadd builtin command when no arguments are supplied. UUIIDD Expands to the user ID of the current user, ini- tialized at shell startup. EEUUIIDD Expands to the effective user ID of the current user, initialized at shell startup. BBAASSHH Expands to the full pathname used to invoke this instance of bbaasshh. BBAASSHH__VVEERRSSIIOONN Expands to the version number of this instance of bbaasshh. SSHHLLVVLL Incremented by one each time an instance of bbaasshh is started. RRAANNDDOOMM Each time this parameter is referenced, a random integer is generated. The sequence of random num- bers may be initialized by assigning a value to RRAANNDDOOMM. If RRAANNDDOOMM is unset, it loses its special properties, even if it is subsequently reset. SSEECCOONNDDSS Each time this parameter is referenced, the number of seconds since shell invocation is returned. If a value is assigned to SSEECCOONNDDSS, the value returned upon subsequent references is the number of seconds since the assignment plus the value assigned. If SSEECCOONNDDSS is unset, it loses its special properties, even if it is subsequently reset. LLIINNEENNOO Each time this parameter is referenced, the shell substitutes a decimal number representing the cur- rent sequential line number (starting with 1) within a script or function. When not in a script or function, the value substituted is not guaran- teed to be meaningful. When in a function, the value is not the number of the source line that the command appears on (that information has been lost by the time the function is executed), but is an approximation of the number of _s_i_m_p_l_e _c_o_m_m_a_n_d_s exe- cuted in the current function. If LLIINNEENNOO is unset, it loses its special properties, even if it is sub- sequently reset. OOPPTTAARRGG The value of the last option argument processed by the ggeettooppttss builtin command (see SSHHEELLLL BBUUIILLTTIINN CCOOMM-- MMAANNDDSS below). OOPPTTIINNDD The index of the last option processed by the ggeettooppttss builtin command (see SSHHEELLLL BBUUIILLTTIINN CCOOMMMMAANNDDSS below). The following variables are used by the shell. In some cases, bbaasshh assigns a default value to a variable; these cases are noted below. IIFFSS The _I_n_t_e_r_n_a_l _F_i_e_l_d _S_e_p_a_r_a_t_o_r that is used for word splitting after expansion and to split lines into words with the rreeaadd builtin command. The default GNU 1993 August 9 8 BASH(1) BASH(1) value is ``''. PPAATTHH The search path for commands. It is a colon- separated list of directories in which the shell looks for commands (see CCOOMMMMAANNDD EEXXEECCUUTTIIOONN below). The default path is system-dependent, and is set by the administrator who installs bbaasshh. A common value is ``.:/usr/gnu/bin:/usr/local/bin:/usr/ucb:/bin:/usr/bin:/etc:/usr/etc''. Note that in some circumstances, however, a leading `.' in PPAATTHH can be a security hazard. HHOOMMEE The home directory of the current user; the default argument for the ccdd builtin command. CCDDPPAATTHH The search path for the ccdd command. This is a colon-separated list of directories in which the shell looks for destination directories specified by the ccdd command. A sample value is ``.:~:/usr''. EENNVV If this parameter is set when bbaasshh is executing a shell script, its value is interpreted as a file- name containing commands to initialize the shell, as in _._b_a_s_h_r_c. The value of EENNVV is subjected to parameter expansion, command substitution, and arithmetic expansion before being interpreted as a pathname. PPAATTHH is not used to search for the resultant pathname. MMAAIILL If this parameter is set to a filename and the MMAAIILLPPAATTHH variable is not set, bbaasshh informs the user of the arrival of mail in the specified file. MMAAIILLCCHHEECCKK Specifies how often (in seconds) bbaasshh checks for mail. The default is 60 seconds. When it is time to check for mail, the shell does so before prompt- ing. If this variable is unset, the shell disables mail checking. MMAAIILLPPAATTHH A colon-separated list of pathnames to be checked for mail. The message to be printed may be speci- fied by separating the pathname from the message with a `?'. $_ stands for the name of the current mailfile. Example: MMAAIILLPPAATTHH='/usr/spool/mail/bfox?"You have mail":~/shell-mail?"$_ has mail!"' BBaasshh supplies a default value for this variable, but the location of the user mail files that it uses is system dependent (e.g., /usr/spool/mail/$$UUSSEERR). MMAAIILL__WWAARRNNIINNGG If set, and a file that bbaasshh is checking for mail has been accessed since the last time it was checked, the message ``The mail in _m_a_i_l_f_i_l_e has been read'' is printed. PPSS11 The value of this parameter is expanded (see PPRROOMMPPTTIINNGG below) and used as the primary prompt string. The default value is ``bbaasshh\\$$ ''. PPSS22 The value of this parameter is expanded like PPSS11 GNU 1993 August 9 9 BASH(1) BASH(1) and used as the secondary prompt string. The default is ``>> ''. PPSS44 The value of this parameter is expanded like PPSS11 and the value is printed before each command bbaasshh displays during an execution trace. The first character of PPSS44 is replicated multiple times, as necessary, to indicate multiple levels of indirec- tion. The default is ``++ ''. NNOO__PPRROOMMPPTT__VVAARRSS If set, a decoded prompt string does not undergo further expansion (see PPRROOMMPPTTIINNGG below). HHIISSTTSSIIZZEE The number of commands to remember in the command history (see HHIISSTTOORRYY below). The default value is 500. HHIISSTTFFIILLEE The name of the file in which command history is saved. (See HHIISSTTOORRYY below.) The default value is _~_/_._b_a_s_h___h_i_s_t_o_r_y. If unset, the command history is not saved when an interactive shell exits. HHIISSTTFFIILLEESSIIZZEE The maximum number of lines contained in the his- tory file. When this variable is assigned a value, the history file is truncated, if necessary, to contain no more than that number of lines. The default value is 500. OOPPTTEERRRR If set to the value 1, bbaasshh displays error messages generated by the ggeettooppttss builtin command (see SSHHEELLLL BBUUIILLTTIINN CCOOMMMMAANNDDSS below). OOPPTTEERRRR is initialized to 1 each time the shell is invoked or a shell script is executed. PPRROOMMPPTT__CCOOMMMMAANNDD If set, the value is executed as a command prior to issuing each primary prompt. IIGGNNOORREEEEOOFF iiggnnoorreeeeooff Controls the action of the shell on receipt of an EEOOFF character as the sole input. If set, the value is the number of consecutive EEOOFF characters typed before bbaasshh exits. If the variable exists but does not have a numeric value, or has no value, the default value is 10. If it does not exist, EEOOFF signifies the end of input to the shell. This is only in effect for interactive shells. HHOOSSTTTTYYPPEE Automatically set to a string that uniquely describes the type of machine on which bbaasshh is exe- cuting. The default is system-dependent. TTMMOOUUTT If set to a value greater than zero, the value is interpreted as the number of seconds to wait for input after issuing the primary prompt. BBaasshh ter- minates after waiting for that number of seconds if input does not arrive. FFCCEEDDIITT The default editor for the ffcc builtin command. GNU 1993 August 9 10 BASH(1) BASH(1) FFIIGGNNOORREE A colon-separated list of suffixes to ignore when performing filename completion (see RREEAADDLLIINNEE below). A filename whose suffix matches one of the entries in FFIIGGNNOORREE is excluded from the list of matched filenames. A sample value is ``.o:~''. nnoottiiffyy If set, bbaasshh reports terminated background jobs immediately, rather than waiting until before printing the next primary prompt (see also the --bb option to the sseett builtin command). hhiissttoorryy__ccoonnttrrooll If set to a value of _i_g_n_o_r_e_s_p_a_c_e, lines which begin with a <> are not entered on the history list. If set to a value of _i_g_n_o_r_e_d_u_p_s, lines matching the last history line are not entered. If unset, or if set to any other value than those above, all lines read by the parser are saved on the history list. ccoommmmaanndd__oorriieenntteedd__hhiissttoorryy If set, bbaasshh attempts to save all lines of a multi- ple-line command in the same history entry. This allows easy re-editing of multi-line commands. gglloobb__ddoott__ffiilleennaammeess If set, bbaasshh includes filenames beginning with a `.' in the results of pathname expansion. aallllooww__nnuullll__gglloobb__eexxppaannssiioonn If set, bbaasshh allows pathname patterns which match no files (see PPaatthhnnaammee EExxppaannssiioonn below) to expand to a null string, rather than themselves. hhiissttcchhaarrss The two or three characters which control history expansion and tokenization (see HHIISSTTOORRYY EEXXPPAANNSSIIOONN below). The first character is the _h_i_s_t_o_r_y _e_x_p_a_n_- _s_i_o_n _c_h_a_r_a_c_t_e_r, that is, the character which sig- nals the start of a history expansion, normally `!!'. The second character is the _q_u_i_c_k _s_u_b_s_t_i_t_u_- _t_i_o_n character, which is used as shorthand for re- running the previous command entered, substituting one string for another in the command. The default is `^^'. The optional third character is the char- acter which signifies that the remainder of the line is a comment, when found as the first charac- ter of a word, normally `##'. The history comment character causes history substitution to be skipped for the remaining words on the line. It does not necessarily cause the shell parser to treat the rest of the line as a comment. nnoolliinnkkss If set, the shell does not follow symbolic links when executing commands that change the current working directory. It uses the physical directory structure instead. By default, bbaasshh follows the logical chain of directories when performing com- mands such as ccdd. GNU 1993 August 9 11 BASH(1) BASH(1) hhoossttnnaammee__ccoommpplleettiioonn__ffiillee Contains the name of a file in the same format as _/_e_t_c_/_h_o_s_t_s that should be read when the shell needs to complete a hostname. You can change the file interactively; the next time you want to complete a hostname bbaasshh adds the contents of the new file to the already existing database. nnoocclloobbbbeerr If set, bbaasshh does not overwrite an existing file with the >>, >>&&, and <<>> redirection operators. This variable may be overridden when creating output files by using the redirection operator >>|| instead of >> (see also the --CC option to the sseett builtin command). aauuttoo__rreessuummee This variable controls how the shell interacts with the user and job control. If this variable is set, single word simple commands without redirections are treated as candidates for resumption of an existing stopped job. There is no ambiguity allowed; if there is more than one job beginning with the string typed, the job most recently accessed is selected. nnoo__eexxiitt__oonn__ffaaiilleedd__eexxeecc If this variable exists, a non-interactive shell will not exit if it cannot execute the file speci- fied in the eexxeecc builtin command. An interactive shell does not exit if eexxeecc fails. ccddaabbllee__vvaarrss If this is set, an argument to the ccdd builtin com- mand that is not a directory is assumed to be the name of a variable whose value is the directory to change to. EEXXPPAANNSSIIOONN Expansion is performed on the command line after it has been split into words. There are seven kinds of expansion performed: _b_r_a_c_e _e_x_p_a_n_s_i_o_n, _t_i_l_d_e _e_x_p_a_n_s_i_o_n, _p_a_r_a_m_e_t_e_r _a_n_d _v_a_r_i_a_b_l_e _e_x_p_a_n_s_i_o_n, _c_o_m_m_a_n_d _s_u_b_s_t_i_t_u_t_i_o_n, _a_r_i_t_h_m_e_t_i_c _e_x_p_a_n_s_i_o_n, _w_o_r_d _s_p_l_i_t_t_i_n_g, and _p_a_t_h_n_a_m_e _e_x_p_a_n_s_i_o_n. The order of expansions is: brace expansion, tilde expan- sion, parameter, variable, command, and arithmetic substi- tution (done in a left-to-right fashion), word splitting, and pathname expansion. On systems that can support it, there is an additional expansion available: _p_r_o_c_e_s_s _s_u_b_s_t_i_t_u_t_i_o_n. Only brace expansion, word splitting, and pathname expan- sion can change the number of words of the expansion; other expansions expand a single word to a single word. The single exception to this is the expansion of ``$$@@'' as explained above (see PPAARRAAMMEETTEERRSS). GNU 1993 August 9 12 BASH(1) BASH(1) BBrraaccee EExxppaannssiioonn _B_r_a_c_e _e_x_p_a_n_s_i_o_n is a mechanism by which arbitrary strings may be generated. This mechanism is similar to _p_a_t_h_n_a_m_e _e_x_p_a_n_s_i_o_n, but the filenames generated need not exist. Patterns to be brace expanded take the form of an optional _p_r_e_a_m_b_l_e, followed by a series of comma-separated strings between a pair of braces, followed by an optional _p_o_s_t_a_m_- _b_l_e. The preamble is prepended to each string contained within the braces, and the postamble is then appended to each resulting string, expanding left to right. Brace expansions may be nested. The results of each expanded string are not sorted; left to right order is preserved. For example, a{{d,c,b}}e expands into `ade ace abe'. Brace expansion is performed before any other expansions, and any characters special to other expansions are pre- served in the result. It is strictly textual. BBaasshh does not apply any syntactic interpretation to the context of the expansion or the text between the braces. A correctly-formed brace expansion must contain unquoted opening and closing braces, and at least one unquoted comma. Any incorrectly formed brace expansion is left unchanged. This construct is typically used as shorthand when the common prefix of the strings to be generated is longer than in the above example: mkdir /usr/local/src/bash/{old,new,dist,bugs} or chown root /usr/{ucb/{ex,edit},lib/{ex?.?*,how_ex}} Brace expansion introduces a slight incompatibility with traditional versions of sshh, the Bourne shell. sshh does not treat opening or closing braces specially when they appear as part of a word, and preserves them in the output. BBaasshh removes braces from words as a consequence of brace expan- sion. For example, a word entered to sshh as _f_i_l_e_{_1_,_2_} appears identically in the output. The same word is out- put as _f_i_l_e_1 _f_i_l_e_2 after expansion by bbaasshh. If strict compatibility with sshh is desired, start bbaasshh with the --nnoobbrraacceeeexxppaannssiioonn flag (see OOPPTTIIOONNSS above) or disable brace expansion with the ++oo bbrraacceeeexxppaanndd option to the sseett command (see SSHHEELLLL BBUUIILLTTIINN CCOOMMMMAANNDDSS below). TTiillddee EExxppaannssiioonn If a word begins with a tilde character (`~~'), all of the characters preceding the first slash (or all characters, if there is no slash) are treated as a possible _l_o_g_i_n _n_a_m_e. If this _l_o_g_i_n _n_a_m_e is the null string, the tilde is replaced with the value of the parameter HHOOMMEE. If HHOOMMEE is GNU 1993 August 9 13 BASH(1) BASH(1) unset, the home directory of the user executing the shell is substituted instead. If a `+' follows the tilde, the value of PPWWDD replaces the tilde and `+'. If a `-' follows, the value of OOLLDDPPWWDD is substituted. If the value following the tilde is a valid _l_o_g_i_n _n_a_m_e, the tilde and _l_o_g_i_n _n_a_m_e are replaced with the home directory associated with that name. If the name is invalid, or the tilde expansion fails, the word is unchanged. Each variable assignment is checked for unquoted instances of tildes following a :: or ==. In these cases, tilde sub- stitution is also performed. Consequently, one may use pathnames with tildes in assignments to PPAATTHH, MMAAIILLPPAATTHH, and CCDDPPAATTHH, and the shell assigns the expanded value. PPaarraammeetteerr EExxppaannssiioonn The `$$' character introduces parameter expansion, command substitution, or arithmetic expansion. The parameter name or symbol to be expanded may be enclosed in braces, which are optional but serve to protect the variable to be expanded from characters immediately following it which could be interpreted as part of the name. ${_p_a_r_a_m_e_t_e_r} The value of _p_a_r_a_m_e_t_e_r is substituted. The braces are required when _p_a_r_a_m_e_t_e_r is a positional parame- ter with more than one digit, or when _p_a_r_a_m_e_t_e_r is followed by a character which is not to be inter- preted as part of its name. In each of the cases below, _w_o_r_d is subject to tilde expansion, parameter expansion, command substitution, and arithmetic expansion. BBaasshh tests for a parameter that is unset or null; omitting the colon results in a test only for a parameter that is unset. ${_p_a_r_a_m_e_t_e_r::--_w_o_r_d} UUssee DDeeffaauulltt VVaalluueess. If _p_a_r_a_m_e_t_e_r is unset or null, the expansion of _w_o_r_d is substituted. Otherwise, the value of _p_a_r_a_m_e_t_e_r is substituted. ${_p_a_r_a_m_e_t_e_r::==_w_o_r_d} AAssssiiggnn DDeeffaauulltt VVaalluueess. If _p_a_r_a_m_e_t_e_r is unset or null, the expansion of _w_o_r_d is assigned to _p_a_r_a_m_e_- _t_e_r. The value of _p_a_r_a_m_e_t_e_r is then substituted. Positional parameters and special parameters may not be assigned to in this way. ${_p_a_r_a_m_e_t_e_r::??_w_o_r_d} DDiissppllaayy EErrrroorr iiff NNuullll oorr UUnnsseett. If _p_a_r_a_m_e_t_e_r is null or unset, the expansion of _w_o_r_d (or a message to that effect if _w_o_r_d is not present) is written to the standard error and the shell, if it is not interactive, exits. Otherwise, the value of GNU 1993 August 9 14 BASH(1) BASH(1) _p_a_r_a_m_e_t_e_r is substituted. ${_p_a_r_a_m_e_t_e_r::++_w_o_r_d} UUssee AAlltteerrnnaattee VVaalluuee. If _p_a_r_a_m_e_t_e_r is null or unset, nothing is substituted, otherwise the expan- sion of _w_o_r_d is substituted. ${##_p_a_r_a_m_e_t_e_r} The length in characters of the value of _p_a_r_a_m_e_t_e_r is substituted. If _p_a_r_a_m_e_t_e_r is ** or @@, the length substituted is the length of ** expanded within dou- ble quotes. ${_p_a_r_a_m_e_t_e_r##_w_o_r_d} ${_p_a_r_a_m_e_t_e_r####_w_o_r_d} The _w_o_r_d is expanded to produce a pattern just as in pathname expansion. If the pattern matches the beginning of the value of _p_a_r_a_m_e_t_e_r, then the expansion is the value of _p_a_r_a_m_e_t_e_r with the short- est matching pattern deleted (the ``##'' case) or the longest matching pattern deleted (the ``####'' case). ${_p_a_r_a_m_e_t_e_r%%_w_o_r_d} ${_p_a_r_a_m_e_t_e_r%%%%_w_o_r_d} The _w_o_r_d is expanded to produce a pattern just as in pathname expansion. If the pattern matches a trailing portion of the value of _p_a_r_a_m_e_t_e_r, then the expansion is the value of _p_a_r_a_m_e_t_e_r with the shortest matching pattern deleted (the ``%%'' case) or the longest matching pattern deleted (the ``%%%%'' case). CCoommmmaanndd SSuubbssttiittuuttiioonn _C_o_m_m_a_n_d _s_u_b_s_t_i_t_u_t_i_o_n allows the output of a command to replace the command name. There are two forms: $$((_c_o_m_m_a_n_d)) or ``_c_o_m_m_a_n_d`` BBaasshh performs the expansion by executing _c_o_m_m_a_n_d and replacing the command substitution with the standard out- put of the command, with any trailing newlines deleted. When the old-style backquote form of substitution is used, backslash retains its literal meaning except when followed by $$, ``, or \\. When using the $(_c_o_m_m_a_n_d) form, all char- acters between the parentheses make up the command; none are treated specially. Command substitutions may be nested. To nest when using the old form, escape the inner backquotes with back- slashes. If the substitution appears within double quotes, word GNU 1993 August 9 15 BASH(1) BASH(1) splitting and pathname expansion are not performed on the results. AArriitthhmmeettiicc EExxppaannssiioonn Arithmetic expansion allows the evaluation of an arith- metic expression and the substitution of the result. The format for arithmetic expansion is: $$[[_e_x_p_r_e_s_s_i_o_n]] The _e_x_p_r_e_s_s_i_o_n is treated as if it were within double quotes, but a double quote inside the braces is not treated specially. All tokens in the expression undergo parameter expansion, command substitution, and quote removal. Arithmetic substitutions may be nested. The evaluation is performed according to the rules listed below under AARRIITTHHMMEETTIICC EEVVAALLUUAATTIIOONN. If _e_x_p_r_e_s_s_i_o_n is invalid, bbaasshh prints a message indicating failure and no substitution occurs. PPrroocceessss SSuubbssttiittuuttiioonn _P_r_o_c_e_s_s _s_u_b_s_t_i_t_u_t_i_o_n is supported on systems that support named pipes (_F_I_F_O_s) or the //ddeevv//ffdd method of naming open files. It takes the form of <<((_l_i_s_t)) or >>((_l_i_s_t)). The pro- cess _l_i_s_t is run with its input or output connected to a _F_I_F_O or some file in //ddeevv//ffdd. The name of this file is passed as an argument to the current command as the result of the expansion. If the >>((_l_i_s_t)) form is used, writing to the file will provide input for _l_i_s_t. If the <<((_l_i_s_t)) form is used, the file passed as an argument should be read to obtain the output of _l_i_s_t. On systems that support it, _p_r_o_c_e_s_s _s_u_b_s_t_i_t_u_t_i_o_n is per- formed simultaneously with _p_a_r_a_m_e_t_e_r _a_n_d _v_a_r_i_a_b_l_e _e_x_p_a_n_- _s_i_o_n, _c_o_m_m_a_n_d _s_u_b_s_t_i_t_u_t_i_o_n, and _a_r_i_t_h_m_e_t_i_c _e_x_p_a_n_s_i_o_n. WWoorrdd SSpplliittttiinngg The shell scans the results of parameter expansion, com- mand substitution, and arithmetic expansion that did not occur within double quotes for _w_o_r_d _s_p_l_i_t_t_i_n_g. The shell treats each character of IIFFSS as a delimiter, and splits the results of the other expansions into words on these characters. If the value of IIFFSS is exactly <><><>, the default, then any sequence of IIFFSS characters serves to delimit words; otherwise each occurrence of an IIFFSS character is treated as a delimiter. If the value of IIFFSS is null, no word splitting occurs. IIFFSS cannot be unset. Explicit null arguments ("""" or '''') are retained. Implicit null arguments, resulting from the expansion of _p_a_r_a_m_e_t_e_r_s that have no values, are removed. GNU 1993 August 9 16 BASH(1) BASH(1) Note that if no expansion occurs, no splitting is per- formed. PPaatthhnnaammee EExxppaannssiioonn After word splitting, unless the --ff option has been set, bbaasshh scans each _w_o_r_d for the characters **, ??, and [[. If one of these characters appears, then the word is regarded as a _p_a_t_t_e_r_n, and replaced with an alphabetically sorted list of pathnames matching the pattern. If no matching pathnames are found, and the shell variable aallllooww__nnuullll__gglloobb__eexxppaannssiioonn is unset, the word is left unchanged. If the variable is set, and no matches are found, the word is removed. When a pattern is used for pathname generation, the character ````..'''' at the start of a name or immediately following a slash must be matched explicitly, unless the shell variable gglloobb__ddoott__ffiilleennaammeess is set. The slash character must always be matched explicitly. In other cases, the ````..'''' character is not treated specially. The special pattern characters have the following mean- ings: ** Matches any string, including the null string. ?? Matches any single character. [[......]] Matches any one of the enclosed characters. A pair of characters separated by a minus sign denotes a _r_a_n_g_e; any character lexically between those two characters, inclusive, is matched. If the first character following the [[ is a !! or a ^^ then any character not enclosed is matched. A -- or ]] may be matched by including it as the first or last char- acter in the set. QQuuoottee RReemmoovvaall After the preceding expansions, all unquoted occurrences of the characters \\, ``, and "" are removed. RREEDDIIRREECCTTIIOONN Before a command is executed, its input and output may be _r_e_d_i_r_e_c_t_e_d using a special notation interpreted by the shell. Redirection may also be used to open and close files for the current shell execution environment. The following redirection operators may appear anywhere in a _s_i_m_p_l_e _c_o_m_m_a_n_d or may precede or follow a _c_o_m_m_a_n_d. Redi- rections are processed in the order they appear, from left to right. In the following descriptions, if the file descriptor num- ber is omitted, and the first character of the redirection operator is <<, the redirection refers to the standard input (file descriptor 0). If the first character of the redirection operator is >>, the redirection refers to the standard output (file descriptor 1). GNU 1993 August 9 17 BASH(1) BASH(1) The word that follows the redirection operator in the fol- lowing descriptions is subjected to brace expansion, tilde expansion, parameter expansion, command substitution, arithmetic expansion, quote removal, and pathname expan- sion. If it expands to more than one word, bbaasshh reports an error. Note that the order of redirections is significant. For example, the command ls >> dirlist 2>>&&1 directs both standard output and standard error to the file _d_i_r_l_i_s_t, while the command ls 2>>&&1 >> dirlist directs only the standard output to file _d_i_r_l_i_s_t, because the standard error was duplicated as standard output before the standard output was redirected to _d_i_r_l_i_s_t. RReeddiirreeccttiinngg IInnppuutt Redirection of input causes the file whose name results from the expansion of _w_o_r_d to be opened for reading on file descriptor _n, or the standard input (file descriptor 0) if _n is not specified. The general format for redirecting input is: [_n]<<_w_o_r_d RReeddiirreeccttiinngg OOuuttppuutt Redirection of output causes the file whose name results from the expansion of _w_o_r_d to be opened for writing on file descriptor _n, or the standard output (file descriptor 1) if _n is not specified. If the file does not exist it is created; if it does exist it is truncated to zero size. The general format for redirecting output is: [_n]>>_w_o_r_d If the redirection operator is >>||, then the variable nnoocclloobbbbeerr is not consulted, and the file is created regardless of the value of nnoocclloobbbbeerr (see SShheellll VVaarriiaabblleess above and the --CC option to the sseett builtin command). AAppppeennddiinngg RReeddiirreecctteedd OOuuttppuutt Redirection of output in this fashion causes the file whose name results from the expansion of _w_o_r_d to be opened for appending on file descriptor _n, or the standard output (file descriptor 1) if _n is not specified. If the file does not exist it is created. GNU 1993 August 9 18 BASH(1) BASH(1) The general format for appending output is: [_n]>>>>_w_o_r_d RReeddiirreeccttiinngg SSttaannddaarrdd OOuuttppuutt aanndd SSttaannddaarrdd EErrrroorr BBaasshh allows both the standard output (file descriptor 1) and the standard error output (file descriptor 2) to be redirected to the file whose name is the expansion of _w_o_r_d with this construct. There are two formats for redirecting standard output and standard error: &&>>_w_o_r_d and >>&&_w_o_r_d Of the two forms, the first is preferred. This is seman- tically equivalent to >>_w_o_r_d 2>>&&1 HHeerree DDooccuummeennttss This type of redirection instructs the shell to read input from the current source until a line containing only _w_o_r_d (with no trailing blanks) is seen. All of the lines read up to that point are then used as the standard input for a command. The format of here-documents is as follows: <<<<[--]_w_o_r_d _h_e_r_e_-_d_o_c_u_m_e_n_t _d_e_l_i_m_i_t_e_r No parameter expansion, command substitution, pathname expansion, or arithmetic expansion is performed on _w_o_r_d. If any characters in _w_o_r_d are quoted, the _d_e_l_i_m_i_t_e_r is the result of quote removal on _w_o_r_d, and the lines in the here-document are not expanded. Otherwise, all lines of the here-document are subjected to parameter expansion, command substitution, and arithmetic expansion. In the latter case, the pair \\<> is ignored, and \\ must be used to quote the characters \\, $$, and ``. If the redirection operator is <<<<--, then all leading tab characters are stripped from input lines and the line con- taining _d_e_l_i_m_i_t_e_r. This allows here-documents within shell scripts to be indented in a natural fashion. DDuupplliiccaattiinngg FFiillee DDeessccrriippttoorrss The redirection operator GNU 1993 August 9 19 BASH(1) BASH(1) [_n]<<&&_w_o_r_d is used to duplicate input file descriptors. If _w_o_r_d expands to one or more digits, the file descriptor denoted by _n is made to be a copy of that file descriptor. If _w_o_r_d evaluates to --, file descriptor _n is closed. If _n is not specified, the standard input (file descriptor 0) is used. The operator [_n]>>&&_w_o_r_d is used similarly to duplicate output file descriptors. If _n is not specified, the standard output (file descrip- tor 1) is used. As a special case, if _n is omitted, and _w_o_r_d does not expand to one or more digits, the standard output and standard error are redirected as described pre- viously. OOppeenniinngg FFiillee DDeessccrriippttoorrss ffoorr RReeaaddiinngg aanndd WWrriittiinngg The redirection operator [_n]<<>>_w_o_r_d causes the file whose name is the expansion of _w_o_r_d to be opened for both reading and writing on file descriptor _n, or as the standard input and standard output if _n is not specified. If the file does not exist, it is created. FFUUNNCCTTIIOONNSS A shell function, defined as described above under SSHHEELLLL GGRRAAMMMMAARR, stores a series of commands for later execution. Functions are executed in the context of the current shell; no new process is created to interpret them (con- trast this with the execution of a shell script). When a function is executed, the arguments to the function become the positional parameters during its execution. The spe- cial parameter ## is updated to reflect the change. Posi- tional parameter 0 is unchanged. Variables local to the function may be declared with the llooccaall builtin command. Ordinarily, variables and their values are shared between the function and its caller. If the builtin command rreettuurrnn is executed in a function, the function completes and execution resumes with the next command after the function call. When a function com- pletes, the values of the positional parameters and the special parameter ## are restored to the values they had prior to function execution. Function names may be listed with the --ff option to the ddeeccllaarree or ttyyppeesseett builtin commands. Functions may be GNU 1993 August 9 20 BASH(1) BASH(1) exported so that subshells automatically have them defined with the --ff option to the eexxppoorrtt builtin. Functions may be recursive. No limit is imposed on the number of recursive calls. AALLIIAASSEESS The shell maintains a list of _a_l_i_a_s_e_s that may be set and unset with the aalliiaass and uunnaalliiaass builtin commands (see SSHHEELLLL BBUUIILLTTIINN CCOOMMMMAANNDDSS below). The first word of each command, if unquoted, is checked to see if it has an alias. If so, that word is replaced by the text of the alias. The alias name and the replacement text may con- tain any valid shell input, including the _m_e_t_a_c_h_a_r_a_c_t_e_r_s listed above. The first word of the replacement text is tested for aliases, but a word that is identical to an alias being expanded is not expanded a second time. This means that one may alias llss to llss --FF, for instance, and bbaasshh does not try to recursively expand the replacement text. If the last character of the alias value is a _b_l_a_n_k, then the next command word following the alias is also checked for alias expansion. Aliases are created and listed with the aalliiaass command, and removed with the uunnaalliiaass command. There is no mechanism for using arguments in the replace- ment text, a la ccsshh. If arguments are needed, a shell function should be used. Aliases are not expanded when the shell is not interac- tive. The rules concerning the definition and use of aliases are somewhat confusing. BBaasshh always reads at least one com- plete line of input before executing any of the commands on that line. Aliases are expanded when a command is read, not when it is executed. Therefore, an alias defi- nition appearing on the same line as another command does not take effect until the next line of input is read. This means that the commands following the alias defini- tion on that line are not affected by the new alias. This behavior is also an issue when functions are executed. Aliases are expanded when the function definition is read, not when the function is executed, because a function def- inition is itself a compound command. As a consequence, aliases defined in a function are not available until after that function is executed. To be safe, always put alias definitions on a separate line, and do not use aalliiaass in compound commands. Note that for almost every purpose, aliases are superseded by shell functions. GNU 1993 August 9 21 BASH(1) BASH(1) JJOOBB CCOONNTTRROOLL _J_o_b _c_o_n_t_r_o_l refers to the ability to selectively stop (_s_u_s_p_e_n_d) the execution of processes and continue (_r_e_s_u_m_e) their execution at a later point. A user typically employs this facility via an interactive interface sup- plied jointly by the system's terminal driver and bbaasshh. The shell associates a _j_o_b with each pipeline. It keeps a table of currently executing jobs, which may be listed with the jjoobbss command. When bbaasshh starts a job asyn- chronously (in the _b_a_c_k_g_r_o_u_n_d), it prints a line that looks like: [1] 25647 indicating that this job is job number 1 and that the pro- cess ID of the last process in the pipeline associated with this job is 25647. All of the processes in a single pipeline are members of the same job. BBaasshh uses the _j_o_b abstraction as the basis for job control. To facilitate the implementation of the user interface to job control, the system maintains the notion of a _c_u_r_r_e_n_t _t_e_r_m_i_n_a_l _p_r_o_c_e_s_s _g_r_o_u_p _I_D. Members of this process group (processes whose process group ID is equal to the current terminal process group ID) receive keyboard-generated sig- nals such as SSIIGGIINNTT. These processes are said to be in the _f_o_r_e_g_r_o_u_n_d. _B_a_c_k_g_r_o_u_n_d processes are those whose pro- cess group ID differs from the terminal's; such processes are immune to keyboard-generated signals. Only foreground processes are allowed to read from or write to the termi- nal. Background processes which attempt to read from (write to) the terminal are sent a SSIIGGTTTTIINN ((SSIIGGTTTTOOUU)) sig- nal by the terminal driver, which, unless caught, suspends the process. If the operating system on which bbaasshh is running supports job control, bbaasshh allows you to use it. Typing the _s_u_s_- _p_e_n_d character (typically ^^ZZ, Control-Z) while a process is running causes that process to be stopped and returns you to bbaasshh. Typing the _d_e_l_a_y_e_d _s_u_s_p_e_n_d character (typi- cally ^^YY, Control-Y) causes the process to be stopped when it attempts to read input from the terminal, and control to be returned to bbaasshh. You may then manipulate the state of this job, using the bbgg command to continue it in the background, the ffgg command to continue it in the fore- ground, or the kkiillll command to kill it. A ^^ZZ takes effect immediately, and has the additional side effect of causing pending output and typeahead to be discarded. There are a number of ways to refer to a job in the shell. The character %% introduces a job name. Job number _n may be referred to as %%nn. A job may also be referred to using a prefix of the name used to start it, or using a GNU 1993 August 9 22 BASH(1) BASH(1) substring that appears in its command line. For example, %%ccee refers to a stopped ccee job. If a prefix matches more than one job, bbaasshh reports an error. Using %%??ccee, on the other hand, refers to any job containing the string ccee in its command line. If the substring matches more than one job, bbaasshh reports an error. The symbols %%%% and %%++ refer to the shell's notion of the _c_u_r_r_e_n_t _j_o_b, which is the last job stopped while it was in the foreground. The _p_r_e_- _v_i_o_u_s _j_o_b may be referenced using %%--. In output pertain- ing to jobs (e.g., the output of the jjoobbss command), the current job is always flagged with a ++, and the previous job with a --. Simply naming a job can be used to bring it into the fore- ground: %%11 is a synonym for ````ffgg %%11'''', bringing job 1 from the background into the foreground. Similarly, ````%%11 &&'''' resumes job 1 in the background, equivalent to ````bbgg %%11''''. The shell learns immediately whenever a job changes state. Normally, bbaasshh waits until it is about to print a prompt before reporting changes in a job's status so as to not interrupt any other output. If the variable nnoottiiffyy is set, bbaasshh reports such changes immediately. (See also the --bb option to the sseett builtin command.) If you attempt to exit bbaasshh while jobs are stopped, the shell prints a message warning you. You may then use the jjoobbss command to inspect their status. If you do this, or try to exit again immediately, you are not warned again, and the stopped jobs are terminated. SSIIGGNNAALLSS When bbaasshh is interactive, it ignores SSIIGGTTEERRMM (so that kkiillll 00 does not kill an interactive shell), and SSIIGGIINNTT is caught and handled (so that the wwaaiitt builtin is interrupt- ible). In all cases, bbaasshh ignores SSIIGGQQUUIITT. If job con- trol is in effect, bbaasshh ignores SSIIGGTTTTIINN, SSIIGGTTTTOOUU, and SSIIGGTTSSTTPP. Synchronous jobs started by bbaasshh have signals set to the values inherited by the shell from its parent. When job control is not in effect, background jobs (jobs started with &&) ignore SSIIGGIINNTT and SSIIGGQQUUIITT. Commands run as a result of command substitution ignore the keyboard- generated job control signals SSIIGGTTTTIINN, SSIIGGTTTTOOUU, and SSIIGGTT-- SSTTPP. CCOOMMMMAANNDD EEXXEECCUUTTIIOONN After a command has been split into words, if it results in a simple command and an optional list of arguments, the following actions are taken. If the command name contains no slashes, the shell attempts to locate it. If there exists a shell function GNU 1993 August 9 23 BASH(1) BASH(1) by that name, that function is invoked as described above in FFUUNNCCTTIIOONNSS. If the name does not match a function, the shell searches for it in the list of shell builtins. If a match is found, that builtin is invoked. If the name is neither a shell function nor a builtin, and contains no slashes, bbaasshh searches each element of the PPAATTHH for a directory containing an executable file by that name. If the search is unsuccessful, the shell prints an error message and returns a nonzero exit status. If the search is successful, or if the command name con- tains one or more slashes, the shell executes the named program. Argument 0 is set to the name given, and the remaining arguments to the command are set to the argu- ments given, if any. If this execution fails because the file is not in exe- cutable format, and the file is not a directory, it is assumed to be a _s_h_e_l_l _s_c_r_i_p_t, a file containing shell com- mands. A subshell is spawned to execute it. This sub- shell reinitializes itself, so that the effect is as if a new shell had been invoked to handle the script, with the exception that the locations of commands remembered by the parent (see hhaasshh below under SSHHEELLLL BBUUIILLTTIINN CCOOMMMMAANNDDSS) are retained by the child. If the program is a file beginning with ##!!, the remainder of the first line specifies an interpreter for the pro- gram. The shell executes the specified interpreter on operating systems that do not handle this executable for- mat themselves. The arguments to the interpreter consist of a single optional argument following the interpreter name on the first line of the program, followed by the name of the program, followed by the command arguments, if any. EENNVVIIRROONNMMEENNTT When a program is invoked it is given an array of strings called the _e_n_v_i_r_o_n_m_e_n_t. This is a list of _n_a_m_e-_v_a_l_u_e pairs, of the form _n_a_m_e=_v_a_l_u_e. The shell allows you to manipulate the environment in sev- eral ways. On invocation, the shell scans its own envi- ronment and creates a parameter for each name found, auto- matically marking it for _e_x_p_o_r_t to child processes. Exe- cuted commands inherit the environment. The eexxppoorrtt and ddeeccllaarree --xx commands allow parameters and functions to be added to and deleted from the environment. If the value of a parameter in the environment is modified, the new value becomes part of the environment, replacing the old. The environment inherited by any executed command consists of the shell's initial environment, whose values may be modified in the shell, less any pairs removed by the uunnsseett GNU 1993 August 9 24 BASH(1) BASH(1) command, plus any additions via the eexxppoorrtt and ddeeccllaarree --xx commands. The environment for any _s_i_m_p_l_e _c_o_m_m_a_n_d or function may be augmented temporarily by prefixing it with parameter assignments, as described above in PPAARRAAMMEETTEERRSS. These assignment statements affect only the environment seen by that command. If the --kk flag is set (see the sseett builtin command below), then _a_l_l parameter assignments are placed in the environ- ment for a command, not just those that precede the com- mand name. When bbaasshh invokes an external command, the variable __ is set to the full path name of the command and passed to that command in its environment. EEXXIITT SSTTAATTUUSS For the purposes of the shell, a command which exits with a zero exit status has succeeded. An exit status of zero indicates success. A non-zero exit status indicates fail- ure. When a command terminates on a fatal signal, bbaasshh uses the value of 128+ssiiggnnaall as the exit status. BBaasshh itself returns the exit status of the last command executed, unless a syntax error occurs, in which case it exits with a non-zero value. See also the eexxiitt builtin command below. PPRROOMMPPTTIINNGG When executing interactively, bbaasshh displays the primary prompt PPSS11 when it is ready to read a command, and the secondary prompt PPSS22 when it needs more input to complete a command. BBaasshh allows these prompt strings to be cus- tomized by inserting a number of backslash-escaped special characters that are decoded as follows: \\tt the current time in HH:MM:SS format \\dd the date in "Weekday Month Date" format (e.g., "Tue May 26") \\nn CRLF \\ss the name of the shell, the basename of $$00 (the portion following the final slash) \\ww the current working directory \\WW the basename of the current working direc- tory \\uu the username of the current user \\hh the hostname \\## the command number of this command \\!! the history number of this command \\$$ if the effective UID is 0, a ##, otherwise a $$ \\nnnnnn character code in octal \\\\ a backslash GNU 1993 August 9 25 BASH(1) BASH(1) After the string is decoded, if the variable NNOO__PPRROOMMPPTT__VVAARRSS is not set, it is expanded via parameter expansion, command substitution, arithmetic expansion, and word splitting. RREEAADDLLIINNEE This is the library that handles reading input when using an interactive shell, unless the --nnoolliinneeeeddiittiinngg option is given. By default, the line editing commands are similar to those of emacs. A vi-style line editing interface is also available. In this section, the emacs-style notation is used to denote keystrokes. Control keys are denoted by C-_k_e_y, e.g., C-n means Control-N. Similarly, _m_e_t_a keys are denoted by M-_k_e_y, so M-x means Meta-X. (On keyboards without a _m_e_t_a key, M-_x means ESC _x, i.e., press the Escape key then the _x key. This makes ESC the _m_e_t_a _p_r_e_- _f_i_x. The combination M-C-_x means ESC-Control-_x, or press the Escape key then hold the Control key while pressing the _x key.) The default key-bindings may be changed with an _~_/_._i_n_p_u_t_r_c file. Other programs that use this library may add their own commands and bindings. For example, placing M-Control-u: universal-argument or C-Meta-u: universal-argument into the _~_/_._i_n_p_u_t_r_c would make M-C-u execute the readline command _u_n_i_v_e_r_s_a_l_-_a_r_g_u_m_e_n_t. The following symbolic character names are recognized: _R_U_B_O_U_T, _D_E_L, _E_S_C, _L_F_D, _N_E_W_L_I_N_E, _R_E_T, _R_E_T_U_R_N, _S_P_C, _S_P_A_C_E, and _T_A_B. In addition to command names, readline allows keys to be bound to a string that is inserted when the key is pressed (a _m_a_c_r_o). See the readline documentation for a precise definition of the syntax of key bindings. BBaasshh allows the current readline key bindings to be dis- played or modified with the bbiinndd builtin command. The editing mode may be switched during interactive use by using the --oo option to the sseett builtin command (see SSHHEELLLL BBUUIILLTTIINN CCOOMMMMAANNDDSS below). Readline has variables that can be used to further cus- tomize its behavior. A variable may be set in _~_/_i_n_p_u_t_r_c with a statement of the form sseett _v_a_r_i_a_b_l_e_-_n_a_m_e _v_a_l_u_e Except where noted, readline variables can take the values GNU 1993 August 9 26 BASH(1) BASH(1) OOnn or OOffff. The variables and their default values are: hhoorriizzoonnttaall--ssccrroollll--mmooddee ((OOffff)) When set to OOnn, makes readline use a single line for display, scrolling the input horizontally on a screen line when it becomes longer than the screen width rather than wrapping to a new line. eeddiittiinngg--mmooddee ((eemmaaccss)) Controls whether readline begins with a set of key bindings similar to _e_m_a_c_s or _v_i. eeddiittiinngg--mmooddee can be set to either eemmaaccss or vvii. mmaarrkk--mmooddiiffiieedd--lliinneess ((OOffff)) If set to OOnn, history lines that have been modified are displayed with a preceding asterisk (**). pprreeffeerr--vviissiibbllee--bbeellll ((OOffff)) If set to OOnn, readline uses a visible bell if one is available rather than simply ringing the termi- nal bell. ccoommmmeenntt--bbeeggiinn ((````:: '''')) The string that is inserted in vvii mode when the vvii--ccoommmmeenntt command is executed. mmeettaa--ffllaagg ((OOffff)) If set to OOnn, readline will enable eight-bit input (that is, it will not strip the high bit from the characters it reads), regardless of what the termi- nal claims it can support. ccoonnvveerrtt--mmeettaa ((OOnn)) If set to OOnn, readline will convert characters with the eighth bit set to an ascii key sequence by stripping the eighth bit and prepending an escape character (in effect, using escape as the _m_e_t_a _p_r_e_- _f_i_x). ccoommpplleettiioonn--qquueerryy--iitteemmss ((110000)) This controls when the user is queried about view- ing the number of possible completions generated by the ppoossssiibbllee--ccoommpplleettiioonnss command. It may be set to any integer value greater than or equal to zero. If the number of possible completions is greater than or equal to the value of this variable, the user is asked whether or not he wishes to view them; otherwise they are simply listed on the ter- minal. Readline commands may be given numeric _a_r_g_u_m_e_n_t_s, which normally act as a repeat count. Sometimes, however, it is the sign of the argument that is significant. Passing a negative argument to a command that acts in the forward direction (e.g., kkiillll--lliinnee) causes that command to act in a backward direction. Commands whose behavior with argu- ments deviates from this are noted. When a command is described as _k_i_l_l_i_n_g text, the text deleted is saved for possible future retrieval (_y_a_n_k_i_n_g). The killed text is saved in a _k_i_l_l_-_r_i_n_g. Consecutive GNU 1993 August 9 27 BASH(1) BASH(1) kills cause the text to be accumulated into one unit, which can be yanked all at once. Commands which do not kill text separate the chunks of text on the kill-ring. The following is a list of the names of the commands and the default key sequences to which they are bound. CCoommmmaannddss ffoorr MMoovviinngg bbeeggiinnnniinngg--ooff--lliinnee ((CC--aa)) Move to the start of the current line. eenndd--ooff--lliinnee ((CC--ee)) Move to the end of the line. ffoorrwwaarrdd--cchhaarr ((CC--ff)) Move forward a character. bbaacckkwwaarrdd--cchhaarr ((CC--bb)) Move back a character. ffoorrwwaarrdd--wwoorrdd ((MM--ff)) Move forward to the end of the next word. Words are composed of alphanumeric characters (letters and digits). bbaacckkwwaarrdd--wwoorrdd ((MM--bb)) Move back to the start of this, or the previous, word. Words are composed of alphanumeric charac- ters (letters and digits). cclleeaarr--ssccrreeeenn ((CC--ll)) Clear the screen leaving the current line at the top of the screen. With an argument, refresh the current line without clearing the screen. CCoommmmaannddss ffoorr MMaanniippuullaattiinngg tthhee HHiissttoorryy aacccceepptt--lliinnee ((NNeewwlliinnee,, RReettuurrnn)) Accept the line regardless of where the cursor is. If this line is non-empty, add it to the history list according to the state of the hhiissttoorryy__ccoonnttrrooll variable. If the line is a modified history line, then restore the history line to its original state. pprreevviioouuss--hhiissttoorryy ((CC--pp)) Fetch the previous command from the history list, moving back in the list. nneexxtt--hhiissttoorryy ((CC--nn)) Fetch the next command from the history list, mov- ing forward in the list. bbeeggiinnnniinngg--ooff--hhiissttoorryy ((MM--<<)) Move to the first line in the history. eenndd--ooff--hhiissttoorryy ((MM-->>)) Move to the end of the input history, i.e., the line currently being entered. rreevveerrssee--sseeaarrcchh--hhiissttoorryy ((CC--rr)) Search backward starting at the current line and moving `up' through the history as necessary. This is an incremental search. ffoorrwwaarrdd--sseeaarrcchh--hhiissttoorryy ((CC--ss)) Search forward starting at the current line and GNU 1993 August 9 28 BASH(1) BASH(1) moving `down' through the history as necessary. This is an incremental search. nnoonn--iinnccrreemmeennttaall--rreevveerrssee--sseeaarrcchh--hhiissttoorryy ((MM--NN)) Search backward through the history starting at the current line using a non-incremental search. nnoonn--iinnccrreemmeennttaall--ffoorrwwaarrdd--sseeaarrcchh--hhiissttoorryy ((MM--PP)) Search forward through the history using a non-incremental search. sshheellll--eexxppaanndd--lliinnee ((MM--CC--ee)) Expand the line the way the shell does when it reads it. This performs alias and history expan- sion as well as all of the shell word expansions. See HHIISSTTOORRYY EEXXPPAANNSSIIOONN below for a description of history expansion. iinnsseerrtt--llaasstt--aarrgguummeenntt ((MM--..,, MM--__)) Insert the last argument to the previous command (the last word on the previous line). With an argument _n, insert the _nth word from the previous command (the words in the previous command begin with word 0). A negative argument inserts the _nth word from the end of the previous command. ooppeerraattee--aanndd--ggeett--nneexxtt ((CC--oo)) Accept the current line for execution and fetch the next line relative to the current line from the history for editing. Any argument is ignored. CCoommmmaannddss ffoorr CChhaannggiinngg TTeexxtt ddeelleettee--cchhaarr ((CC--dd)) Delete the character under the cursor. If the cur- sor is at the beginning of the line, and there are no characters in the line, and the last character typed was not CC--dd, then return EEOOFF. bbaacckkwwaarrdd--ddeelleettee--cchhaarr ((RRuubboouutt)) Delete the character behind the cursor. When given a numeric argument, save the deleted text on the kill-ring. qquuootteedd--iinnsseerrtt ((CC--qq,, CC--vv)) Add the next character that you type to the line verbatim. This is how to insert characters like C-q, for example. ttaabb--iinnsseerrtt ((CC--vv TTAABB)) Insert a tab character. sseellff--iinnsseerrtt ((aa,, bb,, AA,, 11,, !!,, ......)) Insert the character typed. ttrraannssppoossee--cchhaarrss ((CC--tt)) Drag the character before point forward over the character at point. Point moves forward as well. If point is at the end of the line, then transpose the two characters before point. Negative argu- ments don't work. ttrraannssppoossee--wwoorrddss ((MM--tt)) Drag the word behind the cursor past the word in front of the cursor moving the cursor over that word as well. GNU 1993 August 9 29 BASH(1) BASH(1) uuppccaassee--wwoorrdd ((MM--uu)) Uppercase the current (or following) word. With a negative argument, do the previous word, but do not move point. ddoowwnnccaassee--wwoorrdd ((MM--ll)) Lowercase the current (or following) word. With a negative argument, do the previous word, but do not move point. ccaappiittaalliizzee--wwoorrdd ((MM--cc)) Capitalize the current (or following) word. With a negative argument, do the previous word, but do not move point. KKiilllliinngg aanndd YYaannkkiinngg kkiillll--lliinnee ((CC--kk)) Kill the text from the current cursor position to the end of the line. bbaacckkwwaarrdd--kkiillll--lliinnee Kill backward to the beginning of the line. This is normally unbound. kkiillll--wwoorrdd ((MM--dd)) Kill from the cursor to the end of the current word, or if between words, to the end of the next word. Word boundaries are the same as those used by ffoorrwwaarrdd--wwoorrdd. bbaacckkwwaarrdd--kkiillll--wwoorrdd ((MM--RRuubboouutt)) Kill the word behind the cursor. Word boundaries are the same as those used by bbaacckkwwaarrdd--wwoorrdd. uunniixx--lliinnee--ddiissccaarrdd ((CC--uu)) Kill backward from point to the beginning of the line. uunniixx--wwoorrdd--rruubboouutt ((CC--ww)) Kill the word behind the cursor, using white space as a word boundary. The word boundaries are dif- ferent from backward-kill-word. yyaannkk ((CC--yy)) Yank the top of the kill ring into the buffer at the cursor. yyaannkk--ppoopp ((MM--yy)) Rotate the kill-ring, and yank the new top. Only works following yyaannkk or yyaannkk--ppoopp. NNuummeerriicc AArrgguummeennttss ddiiggiitt--aarrgguummeenntt ((MM--00,, MM--11,, ......,, MM----)) Add this digit to the argument already accumulat- ing, or start a new argument. M-- starts a nega- tive argument. uunniivveerrssaall--aarrgguummeenntt Each time this is executed, the argument count is multiplied by four. The argument count is ini- tially one, so executing this function the first time makes the argument count four. By default, this is not bound to a key. GNU 1993 August 9 30 BASH(1) BASH(1) CCoommpplleettiinngg ccoommpplleettee ((TTAABB)) Attempt to perform completion on the text before point. BBaasshh attempts completion treating the text as a variable (if the text begins with $$), username (if the text begins with ~~), hostname (if the text begins with @@), or command (including aliases and functions) in turn. If none of these produces a match, filename completion is attempted. ppoossssiibbllee--ccoommpplleettiioonnss ((MM--??)) List the possible completions of the text before point. iinnsseerrtt--ccoommpplleettiioonnss Insert all completions of the text before point that would have been generated by ppoossssii-- bbllee--ccoommpplleettiioonnss. By default, this is not bound to a key. ccoommpplleettee--ffiilleennaammee ((MM--//)) Attempt filename completion on the text before point. ppoossssiibbllee--ffiilleennaammee--ccoommpplleettiioonnss ((CC--xx //)) List the possible completions of the text before point, treating it as a filename. ccoommpplleettee--uusseerrnnaammee ((MM--~~)) Attempt completion on the text before point, treat- ing it as a username. ppoossssiibbllee--uusseerrnnaammee--ccoommpplleettiioonnss ((CC--xx ~~)) List the possible completions of the text before point, treating it as a username. ccoommpplleettee--vvaarriiaabbllee ((MM--$$)) Attempt completion on the text before point, treat- ing it as a shell variable. ppoossssiibbllee--vvaarriiaabbllee--ccoommpplleettiioonnss ((CC--xx $$)) List the possible completions of the text before point, treating it as a shell variable. ccoommpplleettee--hhoossttnnaammee ((MM--@@)) Attempt completion on the text before point, treat- ing it as a hostname. ppoossssiibbllee--hhoossttnnaammee--ccoommpplleettiioonnss ((CC--xx @@)) List the possible completions of the text before point, treating it as a hostname. ccoommpplleettee--ccoommmmaanndd ((MM--!!)) Attempt completion on the text before point, treat- ing it as a command name. Command completion attempts to match the text against aliases, reserved words, shell functions, builtins, and finally executable filenames, in that order. ppoossssiibbllee--ccoommmmaanndd--ccoommpplleettiioonnss ((CC--xx !!)) List the possible completions of the text before point, treating it as a command name. ddyynnaammiicc--ccoommpplleettee--hhiissttoorryy ((MM--TTAABB)) Attempt completion on the text before point, com- paring the text against lines from the history list for possible completion matches. GNU 1993 August 9 31 BASH(1) BASH(1) ccoommpplleettee--iinnttoo--bbrraacceess ((MM--{{)) Perform filename completion and return the list of possible completions enclosed within braces so the list is available to the shell (see BBrraaccee EExxppaannssiioonn above). MMiisscceellllaanneeoouuss aabboorrtt ((CC--gg)) Abort the current editing command and ring the ter- minal's bell (subject to the setting of pprree-- ffeerr--vviissiibbllee--bbeellll). ddoo--uuppppeerrccaassee--vveerrssiioonn ((MM--aa,, MM--bb,, ......)) Run the command that is bound to the uppercased key. pprreeffiixx--mmeettaa ((EESSCC)) Metafy the next character typed. EESSCC f is equiva- lent to MMeettaa--ff. uunnddoo ((CC--__,, CC--xx CC--uu)) Incremental undo, separately remembered for each line. rreevveerrtt--lliinnee ((MM--rr)) Undo all changes made to this line. This is like typing the uunnddoo command enough times to return the line to its initial state. ddiissppllaayy--sshheellll--vveerrssiioonn ((CC--xx CC--vv)) Display version information about the current instance of bbaasshh. eemmaaccss--eeddiittiinngg--mmooddee ((CC--ee)) When in vvii editing mode, this causes a switch to eemmaaccss editing mode. HHIISSTTOORRYY When interactive, the shell provides access to the _c_o_m_m_a_n_d _h_i_s_t_o_r_y, the list of commands previously typed. The text of the last HHIISSTTSSIIZZEE commands (default 500) is saved in a history list. The shell stores each command in the his- tory list prior to parameter and variable expansion (see EEXXPPAANNSSIIOONN above) but after history expansion is performed, subject to the values of the shell variables ccoomm-- mmaanndd__oorriieenntteedd__hhiissttoorryy and hhiissttoorryy__ccoonnttrrooll. On startup, the history is initialized from the file named by the variable HHIISSTTFFIILLEE (default _~_/_._b_a_s_h___h_i_s_t_o_r_y). HHIISSTTFFIILLEE is truncated, if necessary, to contain no more than HHIISSTTFFIILLEE-- SSIIZZEE lines. The builtin command ffcc (see SSHHEELLLL BBUUIILLTTIINN CCOOMMMMAANNDDSS below) may be used to list or edit and re-execute a portion of the history list. The hhiissttoorryy builtin can be used to display the history list and manipulate the his- tory file. When using the command-line editing, search commands are available in each editing mode that provide access to the history list. When an interactive shell exits, the last HHIISSTTSSIIZZEE lines are copied from the history list to HHIISSTTFFIILLEE. If HHIISSTTFFIILLEE is unset, or if the history file is unwritable, the history is not saved. GNU 1993 August 9 32 BASH(1) BASH(1) HHIISSTTOORRYY EEXXPPAANNSSIIOONN The shell supports a history expansion feature that is similar to the history expansion in ccsshh.. This section describes what syntax features are available. This fea- ture is enabled by default for interactive shells, and can be disabled using the ++HH option to the sseett builtin command (see SSHHEELLLL BBUUIILLTTIINN CCOOMMMMAANNDDSS below). Non-interactive shells do not perform history expansion. History expansion is performed immediately after a com- plete line is read, before the shell breaks it into words. It takes place in two parts. The first is to determine which line from the previous history to use during substi- tution. The second is to select portions of that line for inclusion into the current one. The line selected from the previous history is the _e_v_e_n_t, and the portions of that line that are acted upon are _w_o_r_d_s. The line is bro- ken into words in the same fashion as when reading input, so that several _m_e_t_a_c_h_a_r_a_c_t_e_r-separated words surrounded by quotes are considered as one word. Only backslash (\\) can quote the history escape character, which is !! by default. The shell allows control of the various characters used by the history expansion mechanism (see the description of hhiissttcchhaarrss above under SShheellll VVaarriiaabblleess). EEvveenntt DDeessiiggnnaattoorrss An event designator is a reference to a command line entry in the history list. !! Start a history substitution, except when followed by a , , , = or (. !!!! Refer to the previous command. This is a synonym for `!-1'. !!_n Refer to command line _n. !!--_n Refer to the current command line minus _n. !!_s_t_r_i_n_g Refer to the most recent command starting with _s_t_r_i_n_g. !!??_s_t_r_i_n_g[[??]] Refer to the most recent command containing _s_t_r_i_n_g. ^^_s_t_r_i_n_g_1^^_s_t_r_i_n_g_2^^ Quick substitution. Repeat the last command, replacing _s_t_r_i_n_g_1 with _s_t_r_i_n_g_2. Equivalent to ``!!:s^_s_t_r_i_n_g_1^_s_t_r_i_n_g_2^'' (see MMooddiiffiieerrss below). !!## The entire command line typed so far. WWoorrdd DDeessiiggnnaattoorrss A :: separates the event specification from the word desig- nator. It can be omitted if the word designator begins with a ^^, $$, **, or %%. Words are numbered from the begin- ning of the line, with the first word being denoted by a 0 (zero). GNU 1993 August 9 33 BASH(1) BASH(1) 00 ((zzeerroo)) The zeroth word. For the shell, this is the com- mand word. _n The _nth word. ^^ The first argument. That is, word 1. $$ The last argument. %% The word matched by the most recent `?_s_t_r_i_n_g?' search. _x--_y A range of words; `-_y' abbreviates `0-_y'. ** All of the words but the zeroth. This is a synonym for `1-$$'. It is not an error to use ** if there is just one word in the event; the empty string is returned in that case. MMooddiiffiieerrss After the optional word designator, you can add a sequence of one or more of the following modifiers, each preceded by a `:'. hh Remove a trailing pathname component, leaving only the head. rr Remove a trailing suffix of the form ".xxx", leav- ing the basename. ee Remove all but the suffix. tt Remove all leading pathname components, leaving the tail. pp Print the new command but do not execute it. This takes effect immediately, so it should be the last specifier on the line. ss//_o_l_d//_n_e_w// Substitute _n_e_w for the first occurrence of _o_l_d in the event line. Any delimiter can be used in place of /. The final delimiter is optional if it is the last character of the event line. gg Cause changes to be applied over the entire event line. This is used in conjunction with `::ss'. Any delimiter can be used in place of /. The final delimiter is optional if it is the last character of the event line. AARRIITTHHMMEETTIICC EEVVAALLUUAATTIIOONN The shell allows arithmetic expressions to be evaluated, under certain circumstances (see the lleett builtin command and AArriitthhmmeettiicc EExxppaannssiioonn). Evaluation is done in long integers with no check for overflow, though division by 0 is trapped and flagged as an error. The following list of operators is grouped into levels of equal-precedence oper- ators. The levels are listed in order of decreasing precedence. -- ++ unary minus and plus !! ~~ logical and bitwise negation ** // %% multiplication, division, remainder ++ -- addition, subtraction GNU 1993 August 9 34 BASH(1) BASH(1) <<<< >>>> left and right bitwise shifts <<== >>== << >> comparison ==== !!== equality and inequality && bitwise AND ^^ bitwise exclusive OR || bitwise OR &&&& logical AND |||| logical OR == **== //== %%== ++== --== <<<<== >>>>== &&== ^^== ||== assignment Shell variables are allowed as operands; parameter expan- sion is performed before the expression is evaluated. The value of a parameter is coerced to a long integer within an expression. A shell variable need not have its integer attribute turned on to be used in an expression. Operators are evaluated in order of precedence. Sub- expressions in parentheses are evaluated first and may override the precedence rules above. SSHHEELLLL BBUUIILLTTIINN CCOOMMMMAANNDDSS :: [_a_r_g_u_m_e_n_t_s] No effect; the command does nothing beyond expand- ing _a_r_g_u_m_e_n_t_s and performing any specified redirec- tions. A zero exit code is returned. .. _f_i_l_e_n_a_m_e [_a_r_g_u_m_e_n_t_s] ssoouurrccee _f_i_l_e_n_a_m_e [_a_r_g_u_m_e_n_t_s] Read and execute commands from _f_i_l_e_n_a_m_e in the cur- rent shell environment and return the exit status of the last command executed from _f_i_l_e_n_a_m_e. If _f_i_l_e_n_a_m_e does not contain a slash, pathnames in PPAATTHH are used to find the directory containing _f_i_l_e_n_a_m_e. The file searched for in PPAATTHH need not be executable. The current directory is searched if no file is found in PPAATTHH. If any _a_r_g_u_m_e_n_t_s are supplied, they become the positional parameters when _f_i_l_e is executed. Otherwise the positional parameters are unchanged. The return status is the status of the last command exited within the script (0 if no commands are executed), and false if _f_i_l_e_- _n_a_m_e is not found. aalliiaass [_n_a_m_e[=_v_a_l_u_e] ...] AAlliiaass with no arguments prints the list of aliases in the form _n_a_m_e=_v_a_l_u_e on standard output. When arguments are supplied, an alias is defined for each _n_a_m_e whose _v_a_l_u_e is given. A trailing space in _v_a_l_u_e causes the next word to be checked for alias substitution when the alias is expanded. For each _n_a_m_e in the argument list for which no _v_a_l_u_e is supplied, the name and value of the alias is GNU 1993 August 9 35 BASH(1) BASH(1) printed. AAlliiaass returns true unless a _n_a_m_e is given for which no alias has been defined. bbgg [_j_o_b_s_p_e_c] Place _j_o_b_s_p_e_c in the background, as if it had been started with &&. If _j_o_b_s_p_e_c is not present, the shell's notion of the _c_u_r_r_e_n_t _j_o_b is used. bbgg _j_o_b_- _s_p_e_c returns 0 unless run when job control is dis- abled or, when run with job control enabled, if _j_o_b_s_p_e_c was not found or started without job con- trol. bbiinndd [--mm _k_e_y_m_a_p] [--llvvdd] [--qq _n_a_m_e] bbiinndd [--mm _k_e_y_m_a_p] --ff _f_i_l_e_n_a_m_e bbiinndd [--mm _k_e_y_m_a_p] _k_e_y_s_e_q:_f_u_n_c_t_i_o_n_-_n_a_m_e Display current rreeaaddlliinnee key and function bindings, or bind a key sequence to a rreeaaddlliinnee function or macro. The binding syntax accepted is identical to that of _._i_n_p_u_t_r_c, but each binding must be passed as a separate argument; e.g., '"\C-x\C-r": re-read- init-file'. Options, if supplied, have the follow- ing meanings: --mm _k_e_y_m_a_p Use _k_e_y_m_a_p as the keymap to be affected by the subsequent bindings. Acceptable _k_e_y_m_a_p names are _e_m_a_c_s_, _e_m_a_c_s_-_s_t_a_n_d_a_r_d_, _e_m_a_c_s_-_m_e_t_a_, _e_m_a_c_s_-_c_t_l_x_, _v_i_, _v_i_-_m_o_v_e_, _v_i_-_c_o_m_m_a_n_d, and _v_i_- _i_n_s_e_r_t. _v_i is equivalent to _v_i_-_c_o_m_m_a_n_d. --ll List the names of all rreeaaddlliinnee functions --vv List current function names and bindings --dd Dump function names and bindings in such a way that they can be re-read --ff _f_i_l_e_n_a_m_e Read key bindings from _f_i_l_e_n_a_m_e --qq _f_u_n_c_t_i_o_n Query about which keys invoke the named _f_u_n_c_t_i_o_n The return value is 0 unless an unrecognized option is given or an error occurred. bbrreeaakk [_n] Exit from within a ffoorr, wwhhiillee, or uunnttiill loop. If _n is specified, break _n levels. _n must be >= 1. If _n is greater than the number of enclosing loops, all enclosing loops are exited. The return value is 0 unless the shell is not executing a loop when bbrreeaakk is executed. bbuuiillttiinn _s_h_e_l_l_-_b_u_i_l_t_i_n [_a_r_g_u_m_e_n_t_s] Execute the specified shell builtin, passing it _a_r_g_u_m_e_n_t_s, and return its exit status. This is useful when you wish to define a function whose name is the same as a shell builtin, but need the GNU 1993 August 9 36 BASH(1) BASH(1) functionality of the builtin within the function itself. The ccdd builtin is commonly redefined this way. The return status is false if _s_h_e_l_l_-_b_u_i_l_t_i_n is not a shell builtin command. ccdd [_d_i_r] Change the current directory to _d_i_r. The variable HHOOMMEE is the default _d_i_r. The variable CCDDPPAATTHH defines the search path for the directory contain- ing _d_i_r. Alternative directory names are separated by a colon (:). A null directory name in CCDDPPAATTHH is the same as the current directory, i.e., ``..''. If _d_i_r begins with a slash (/), then CCDDPPAATTHH is not used. An argument of -- is equivalent to $$OOLLDDPPWWDD. The return value is true if the directory was suc- cessfully changed; false otherwise. ccoommmmaanndd [--ppVVvv] _c_o_m_m_a_n_d [_a_r_g ...] Run _c_o_m_m_a_n_d with _a_r_g_s suppressing the normal shell function lookup. Only builtin commands or commands found in the PPAATTHH are executed. If the --pp option is given, the search for _c_o_m_m_a_n_d is performed using a default value for PPAATTHH that is guaranteed to find all of the standard utilities. If either the --VV or --vv option is supplied, a description of _c_o_m_m_a_n_d is printed. The --vv option causes a single word indi- cating the command or pathname used to invoke _c_o_m_- _m_a_n_d to be printed; the --VV option produces a more verbose description. An argument of ---- disables option checking for the rest of the arguments. If the --VV or --vv option is supplied, the exit status is 0 if _c_o_m_m_a_n_d was found, and 1 if not. If neither option is supplied and an error occurred or _c_o_m_m_a_n_d cannot be found, the exit status is 127. Other- wise, the exit status of the ccoommmmaanndd builtin is the exit status of _c_o_m_m_a_n_d. ccoonnttiinnuuee [_n] Resume the next iteration of the enclosing ffoorr, wwhhiillee, or uunnttiill loop. If _n is specified, resume at the _nth enclosing loop. _n must be >= 1. If _n is greater than the number of enclosing loops, the last enclosing loop (the `top-level' loop) is resumed. The return value is 0 unless the shell is not executing a loop when ccoonnttiinnuuee is executed. ddeeccllaarree [--ffrrxxii] [_n_a_m_e[=_v_a_l_u_e]] ttyyppeesseett [--ffrrxxii] [_n_a_m_e[=_v_a_l_u_e]] Declare variables and/or give them attributes. If no _n_a_m_es are given, then display the values of variables instead. The options can be used to restrict output to variables with the specified attribute. --ff Use function names only GNU 1993 August 9 37 BASH(1) BASH(1) --rr Make _n_a_m_es readonly. These names cannot then be assigned values by subsequent assignment statements. --xx Mark _n_a_m_es for export to subsequent commands via the environment. --ii The variable is treated as an integer; arithmetic evaluation (see AARRIITTHHMMEETTIICC EEVVAALLUU-- AATTIIOONN )) is performed when the variable is assigned a value. Using `+' instead of `-' turns off the attribute instead. When used in a function, makes _n_a_m_es local, as with the llooccaall command. The return value is 0 unless an illegal option is encountered, an attempt is made to define a function using "-f foo=bar", an attempt is made to turn off readonly status for a readonly variable, or an attempt is made to display a non-existant function with -f. ddiirrss [[--ll]] Display the list of currently remembered directo- ries. Directories are added to the list with the ppuusshhdd command; the ppooppdd command moves back up through the list. The --ll option produces a longer listing; the default listing format uses a tilde to denote the home directory. The return value is 0 unless an illegal option is supplied. eecchhoo [--nneeEE] [_a_r_g ...] Output the _a_r_gs, separated by spaces. The return status is always 0. If --nn is specified, the trail- ing newline is suppressed. If the --ee option is given, interpretation of the following backslash- escaped characters is enabled. The --EE option dis- ables the interpretation of these escape charac- ters, even on systems where they are interpreted by default. \\aa alert (bell) \\bb backspace \\cc suppress trailing newline \\ff form feed \\nn new line \\rr carriage return \\tt horizontal tab \\vv vertical tab \\\\ backslash \\nnnnnn the character whose ASCII code is _n_n_n (octal) eennaabbllee [--nn] [--aallll] [_n_a_m_e ...] Enable and disable builtin shell commands. This allows the execution of a disk command which has the same name as a shell builtin without specifying a full pathname. If --nn is used, each _n_a_m_e is GNU 1993 August 9 38 BASH(1) BASH(1) disabled; otherwise, _n_a_m_e_s are enabled. For exam- ple, to use the tteesstt found in PPAATTHH instead of the shell builtin version, type ``enable -n test''. If no arguments are given, a list of all enabled shell builtins is printed. If only --nn is supplied, a list of all disabled builtins is printed. If only --aallll is supplied, the list printed includes all builtins, with an indication of whether or not each is enabled. eennaabbllee accepts --aa as a synonym for --aallll. The return value is 0 unless a _n_a_m_e is not a shell builtin. eevvaall [_a_r_g ...] The _a_r_gs are read and concatenated together into a single command. This command is then read and exe- cuted by the shell, and its exit status is returned as the value of the eevvaall command. If there are no _a_r_g_s, or only null arguments, eevvaall returns true. eexxeecc [[--] _c_o_m_m_a_n_d [_a_r_g_u_m_e_n_t_s]] If _c_o_m_m_a_n_d is specified, it replaces the shell. No new process is created. The _a_r_g_u_m_e_n_t_s become the arguments to _c_o_m_m_a_n_d. If the first argument is --, the shell places a dash in the zeroth arg passed to _c_o_m_m_a_n_d. This is what login does. If the file cannot be executed for some reason, a non- interactive shell exits, unless the shell variable nnoo__eexxiitt__oonn__ffaaiilleedd__eexxeecc exists, in which case it returns failure. An interactive shell returns failure if the file cannot be executed. If _c_o_m_m_a_n_d is not specified, any redirections take effect in the current shell, and the return status is 0. eexxiitt [_n] bbyyee [_n] Cause the shell to exit with a status of _n. If _n is omitted, the exit status is that of the last command executed. A trap on EEXXIITT is executed before the shell terminates. eexxppoorrtt [--nnff] [_n_a_m_e[=_w_o_r_d]] ... eexxppoorrtt --pp The supplied _n_a_m_e_s are marked for automatic export to the environment of subsequently executed com- mands. If the --ff option is given, the _n_a_m_e_s refer to functions. If no _n_a_m_e_s are given, or if the --pp option is supplied, a list of all names that are exported in this shell is printed. The --nn option causes the export property to be removed from the named variables. An argument of ---- disables option checking for the rest of the arguments. eexxppoorrtt returns an exit status of true unless an illegal option is encountered or --ff is supplied with a _n_a_m_e that is not a function. GNU 1993 August 9 39 BASH(1) BASH(1) ffcc [--ee _e_n_a_m_e] [--nnllrr] [_f_i_r_s_t] [_l_a_s_t] ffcc --ss [_p_a_t=_r_e_p] [_c_m_d] Fix Command. In the first form, a range of com- mands from _f_i_r_s_t to _l_a_s_t is selected from the his- tory list. _F_i_r_s_t and _l_a_s_t may be specified as a string (to locate the last command beginning with that string) or as a number (an index into the his- tory list, where a negative number is used as an offset from the current command number). If _l_a_s_t is not specified it is set to the current command for listing (so that ffcc --ll --1100 prints the last 10 commands) and to _f_i_r_s_t otherwise. If _f_i_r_s_t is not specified it is set to the previous command for editing and -16 for listing. The --nn flag suppresses the command numbers when listing. The --rr flag reverses the order of the commands. If the --ll flag is given, the commands are listed on standard output. Otherwise, the edi- tor given by _e_n_a_m_e is invoked on a file containing those commands. If _e_n_a_m_e is not given, the value of the FFCCEEDDIITT variable is used, and the value of EEDDIITTOORR if FFCCEEDDIITT is not set. If neither variable is set, _v_i is used. When editing is complete, the edited commands are echoed and executed. In the second form, the command is re-executed after the substitution _o_l_d=_n_e_w is performed. A useful alias to use with this is ``r=fc -s'', so that typing ``r cc'' runs the last command begin- ning with ``cc'' and typing ``r'' re-executes the last command. If the first form is used, the return value is 0 unless an illegal option is encountered or _f_i_r_s_t or _l_a_s_t specify history lines out of range. If the --ee option is supplied, the return value is the value of the last command executed or failure if an error occurs with the temporary file of commands. If the second form is used, the return status is that of the command re-executed, unless _c_m_d does not spec- ify a valid history line, in which case ffcc returns failure. ffgg [_j_o_b_s_p_e_c] Place _j_o_b_s_p_e_c in the foreground, and make it the current job. If _j_o_b_s_p_e_c is not present, the shell's notion of the _c_u_r_r_e_n_t _j_o_b is used. The return value is that of the command placed into the foreground, or failure if run when job control is disabled or, when run with job control enabled, if _j_o_b_s_p_e_c does not specify a valid job or _j_o_b_s_p_e_c specifies a job that was started without job con- trol. GNU 1993 August 9 40 BASH(1) BASH(1) ggeettooppttss _o_p_t_s_t_r_i_n_g _n_a_m_e [_a_r_g_s] ggeettooppttss is used by shell procedures to parse posi- tional parameters. _o_p_t_s_t_r_i_n_g contains the option letters to be recognized; if a letter is followed by a colon, the option is expected to have an argu- ment, which should be separated from it by white space. Each time it is invoked, ggeettooppttss places the next option in the shell variable _n_a_m_e, initializ- ing _n_a_m_e if it does not exist, and the index of the next argument to be processed into the variable OOPPTTIINNDD. OOPPTTIINNDD is initialized to 1 each time the shell or a shell script is invoked. When an option requires an argument, ggeettooppttss places that argument into the variable OOPPTTAARRGG. The shell does not reset OOPPTTIINNDD automatically; it must be manually reset between multiple calls to ggeettooppttss within the same shell invocation if a new set of parameters is to be used. ggeettooppttss can report errors in two ways. If the first character of _o_p_t_s_t_r_i_n_g is a colon, _s_i_l_e_n_t error reporting is used. In normal operation diag- nostic messages are printed when illegal options or missing option arguments are encountered. If the variable OOPPTTEERRRR is set to 0, no error message will be displayed, even if the first character of _o_p_t_- _s_t_r_i_n_g is not a colon. If an illegal option is seen, ggeettooppttss places ? into _n_a_m_e and, if not silent, prints an error message and unsets OOPPTTAARRGG. If ggeettooppttss is silent, the option character found is placed in OOPPTTAARRGG and no diagnostic message is printed. If a required argument is not found, and ggeettooppttss is not silent, a question mark (??) is placed in _n_a_m_e, OOPPTTAARRGG is unset, and a diagnostic message is printed. If ggeettooppttss is silent, then a colon (::) is placed in _n_a_m_e and OOPPTTAARRGG is set to the option character found. ggeettooppttss normally parses the positional parameters, but if more arguments are given in _a_r_g_s, ggeettooppttss parses those instead. ggeettooppttss returns true if an option, specified or unspecified, is found. It returns false if the end of options is encountered or an error occurs. hhaasshh [--rr] [_n_a_m_e] For each _n_a_m_e, the full pathname of the command is determined and remembered. The --rr option causes the shell to forget all remembered locations. If no arguments are given, information about remem- bered commands is printed. An argument of ---- GNU 1993 August 9 41 BASH(1) BASH(1) disables option checking for the rest of the argu- ments. The return status is true unless a _n_a_m_e is not found or an illegal option is supplied. hheellpp [_p_a_t_t_e_r_n] Display helpful information about builtin commands. If _p_a_t_t_e_r_n is specified, hheellpp gives detailed help on all commands matching _p_a_t_t_e_r_n; otherwise a list of the builtins is printed. The return status is 0 unless no command matches _p_a_t_t_e_r_n. hhiissttoorryy [_n] hhiissttoorryy --rrwwaann [_f_i_l_e_n_a_m_e] With no options, display the command history list with line numbers. Lines listed with with a ** have been modified. An argument of _n lists only the last _n lines. If a non-option argument is sup- plied, it is used as the name of the history file; if not, the value of HHIISSTTFFIILLEE is used. Options, if supplied, have the following meanings: --aa Append the ``new'' history lines (history lines entered since the beginning of the current bash session) to the history file --nn Read the history lines not already read from the history file into the current history list. These are lines appended to the his- tory file since the beginning of the current bash session. --rr read the contents of the history file and use them as the current history --ww write the current history to the history file, overwriting the history file's con- tents. The return value is 0 unless an illegal option is encountered or an error occurs while reading or writing the history file. jjoobbss [--llnnpp] [ _j_o_b_s_p_e_c ... ] jjoobbss --xx _c_o_m_m_a_n_d [ _a_r_g_s ... ] The first form lists the active jobs. The --ll option lists process IDs in addition to the normal information; the --pp option lists only the process ID of the job's process group leader. The --nn option displays only jobs that have changed status since last notfied. If _j_o_b_s_p_e_c is given, output is restricted to information about that job. The return status is 0 unless an illegal option is encountered or an illegal _j_o_b_s_p_e_c is supplied. If the --xx option is supplied, jjoobbss replaces any _j_o_b_s_p_e_c found in _c_o_m_m_a_n_d or _a_r_g_s with the corre- sponding process group ID, and executes _c_o_m_m_a_n_d passing it _a_r_g_s, returning its exit status. GNU 1993 August 9 42 BASH(1) BASH(1) kkiillll [--ss ssiiggssppeecc | --ssiiggssppeecc] [_p_i_d | _j_o_b_s_p_e_c] ... kkiillll --ll [_s_i_g_n_u_m] Send the signal named by _s_i_g_s_p_e_c to the processes named by _p_i_d or _j_o_b_s_p_e_c. _s_i_g_s_p_e_c is either a sig- nal name such as SSIIGGKKIILLLL or a signal number. If _s_i_g_s_p_e_c is a signal name, the name is case insensi- tive and may be given with or without the SSIIGG pre- fix. If _s_i_g_s_p_e_c is not present, then SSIIGGTTEERRMM is assumed. An argument of --ll lists the signal names. If any arguments are supplied when --ll is given, the names of the specified signals are listed, and the return status is 0. An argument of ---- disables option checking for the rest of the arguments. kkiillll returns true if at least one signal was suc- cessfully sent, or false if an error occurs or an illegal option is encountered. lleett _a_r_g [_a_r_g ...] Each _a_r_g is an arithmetic expression to be evalu- ated (see AARRIITTHHMMEETTIICC EEVVAALLUUAATTIIOONN). If the last _a_r_g evaluates to 0, lleett returns 1; 0 is returned other- wise. llooccaall [_n_a_m_e[=_v_a_l_u_e]] Create a local variable named _n_a_m_e, and assign it _v_a_l_u_e. When llooccaall is used within a function, it causes the variable _n_a_m_e to have a visible scope restricted to that function and its children. With no operands, llooccaall writes a list of local variables to the standard output. It is an error to use llooccaall when not within a function. The return sta- tus is 0 unless llooccaall is used outside a function, or an illegal _n_a_m_e is supplied. llooggoouutt Exit a login shell. ppooppdd [++//--nn] Removes entries from the directory stack. With no arguments, removes the top directory from the stack, and performs a ccdd to the new top directory. ++nn removes the _nth entry counting from the left of the list shown by ddiirrss, starting with zero. For example: ``popd +0'' removes the first directory, ``popd +1'' the second. --nn removes the _nth entry counting from the right of the list shown by ddiirrss, starting with zero. For example: ``popd -0'' removes the last directory, ``popd -1'' the next to last. If the ppooppdd command is successful, a ddiirrss is per- formed as well, and the return status is 0. ppooppdd returns false if an illegal option is encountered, the directory stack is empty, a non-existant GNU 1993 August 9 43 BASH(1) BASH(1) directory stack entry is specified, or the direc- tory change fails. ppuusshhdd _d_i_r ppuusshhdd ++//--nn Adds a directory to the top of the directory stack, or rotates the stack, making the new top of the stack the current working directory. With no argu- ments, exchanges the top two directories and returns 0, unless the directory stack is empty. ++nn Rotates the stack so that the _nth directory (counting from the left of the list shown by ddiirrss) is at the top. --nn Rotates the stack so that the _nth directory (counting from the right) is at the top. ddiirr adds _d_i_r to the directory stack at the top, making it the new current working directory. If the ppuusshhdd command is successful, a ddiirrss is per- formed as well. If the first form is used, ppuusshhdd returns 0 unless the cd to _d_i_r fails. With the second form, ppuusshhdd returns 0 unless the directory stack is empty, a non-existant directory stack ele- ment is specified, or the directory change to the specified new current directory fails. ppwwdd Print the absolute pathname of the current working directory. The path printed contains no symbolic links (but see the description of nnoolliinnkkss under SShheellll VVaarriiaabblleess above). The return status is 0 unless an error occurs while reading the pathname of the current directory. rreeaadd [--rr] [_n_a_m_e ...] One line is read from the standard input, and the first word is assigned to the first _n_a_m_e, the sec- ond word to the second _n_a_m_e, and so on, with left- over words assigned to the last _n_a_m_e. Only the characters in IIFFSS are recognized as word delim- iters. If no _n_a_m_e_s are supplied, the line read is assigned to the variable RREEPPLLYY. The return code is zero, unless end-of-file is encountered. If the --rr option is given, a backslash-newline pair is not ignored, and the backslash is considered to be part of the line. rreeaaddoonnllyy [--ff] [_n_a_m_e ...] rreeaaddoonnllyy --pp The given _n_a_m_e_s are marked readonly and the values of these _n_a_m_e_s may not be changed by subsequent assignment. If the --ff option is supplied, the functions corresponding to the _n_a_m_e_s are so marked. If no arguments are given, or if the --pp option is supplied, a list of all readonly names is printed. GNU 1993 August 9 44 BASH(1) BASH(1) An argument of ---- disables option checking for the rest of the arguments. The return status is 0 unless an illegal option is encountered or --ff is supplied with a _n_a_m_e that is not a function. rreettuurrnn [_n] Causes a function to exit with the return value specified by _n. If _n is omitted, the return status is that of the last command executed in the func- tion body. If used outside a function, but during execution of a script by the .. (ssoouurrccee) command, it causes the shell to stop executing that script and return either _n or the exit status of the last command executed within the script as the exit sta- tus of the script. If used outside a function and not during execution of a script by .., the return status is false. sseett [----aaeeffhhkknnooppttuuvvxxllddCCHH] [_a_r_g ...] --aa Automatically mark variables which are mod- ified or created for export to the environ- ment of subsequent commands. --bb Cause the status of terminated background jobs to be reported immediately, rather than before the next primary prompt. (Also see nnoottiiffyy under SShheellll VVaarriiaabblleess above). --ee Exit immediately if a _s_i_m_p_l_e_-_c_o_m_m_a_n_d (see SSHHEELLLL GGRRAAMMMMAARR above) exits with a non-zero status. The shell does not exit if the command that fails is part of an _u_n_t_i_l or _w_h_i_l_e loop, part of an _i_f statement, part of a &&&& or |||| list, or if the command's return value is being inverted via !!. --ff Disable pathname expansion. --hh Locate and remember function commands as functions are defined. Function commands are normally looked up when the function is executed. --kk All keyword arguments are placed in the environment for a command, not just those that precede the command name. --mm Monitor mode. Job control is enabled. This flag is on by default for interactive shells on systems that support it (see JJOOBB CCOONNTTRROOLL above). Background processes run in a separate process group and a line con- taining their exit status is printed upon their completion. --nn Read commands but do not execute them. This may be used to check a shell script for syntax errors. This is ignored for interactive shells. --oo _o_p_t_i_o_n_-_n_a_m_e The _o_p_t_i_o_n_-_n_a_m_e can be one of the GNU 1993 August 9 45 BASH(1) BASH(1) following: aalllleexxppoorrtt Same as --aa. bbrraacceeeexxppaanndd The shell performs brace expansion (see BBrraaccee EExxppaannssiioonn above). This is on by default. eemmaaccss Use an emacs-style command line editing interface. This is enabled by default when the shell is inter- active, unless the shell is started with the --nnoolliinneeeeddiittiinngg option. eerrrreexxiitt Same as --ee. hhiisstteexxppaanndd Same as --HH. iiggnnoorreeeeooff The effect is as if the shell com- mand `IGNOREEOF=10' had been exe- cuted (see SShheellll VVaarriiaabblleess above). iinntteerraaccttiivvee--ccoommmmeennttss Allow a word beginning with ## to cause that word and all remaining characters on that line to be ignored in an interactive shell (see CCOOMMMMEENNTTSS above). mmoonniittoorr Same as --mm. nnoocclloobbbbeerr Same as --CC. nnooeexxeecc Same as --nn. nnoogglloobb Same as --ff. nnoohhaasshh Same as --dd. nnoottiiffyy Same as --bb. nnoouunnsseett Same as --uu. pprriivviilleeggeedd Same as --pp. vveerrbboossee Same as --vv. vvii Use a vi-style command line editing interface. xxttrraaccee Same as --xx. If no _o_p_t_i_o_n_-_n_a_m_e is supplied, the values of the current options are printed. --pp Turn on _p_r_i_v_i_l_e_g_e_d mode. In this mode, the $$EENNVV file is not processed by non-interactive shells, and shell functions are not inherited from the environment. This is enabled automatically on startup if the effective user (group) id is not equal to the real user (group) id. Turning this option off causes the effective user and group ids to be set to the real user and group ids. --tt Exit after reading and executing one com- mand. --uu Treat unset variables as an error when GNU 1993 August 9 46 BASH(1) BASH(1) performing parameter expansion. If expan- sion is attempted on an unset variable, the shell prints an error message, and, if not interactive, exits with a non-zero status. --vv Print shell input lines as they are read. --xx After expanding each _s_i_m_p_l_e_-_c_o_m_m_a_n_d, bbaasshh displays the expanded value of PPSS44, fol- lowed by the command and its expanded argu- ments. --ll Save and restore the binding of _n_a_m_e in a ffoorr _n_a_m_e [in wwoorrdd] command (see SSHHEELLLL GGRRAAMM-- MMAARR above). --dd Disable the hashing of commands that are looked up for execution. Normally, com- mands are remembered in a hash table, and once found, do not have to be looked up again. --CC The effect is as if the shell command `noclobber=' had been executed (see SShheellll VVaarriiaabblleess above). --HH Enable !! style history substitution. This flag is on by by default when the shell is interactive. ---- If no arguments follow this flag, then the positional parameters are unset. Other- wise, the positional parameters are set to the _a_r_gs, even if some of them begin with a --. -- Signal the end of options, cause all remaining _a_r_gs to be assigned to the posi- tional parameters. The --xx and --vv options are turned off. If there are no _a_r_gs, the positional parameters remain unchanged. The flags are off by default unless otherwise noted. Using + rather than - causes these flags to be turned off. The flags can also be specified as options to an invocation of the shell. The current set of flags may be found in $$--. After the option arguments are processed, the remaining _n _a_r_gs are treated as values for the positional parameters and are assigned, in order, to $$11, $$22, ...... $$_n. If no options or _a_r_gs are supplied, all shell variables are printed. The return status is always true unless an illegal option is encountered. sshhiifftt [_n] The positional parameters from _n+1 ... are renamed to $$11 ........ If _n is not given, it is assumed to be 1. The exit status is 1 if _n is greater than $$##; otherwise 0. ssuussppeenndd [--ff] Suspend the execution of this shell until it GNU 1993 August 9 47 BASH(1) BASH(1) receives a SSIIGGCCOONNTT signal. The --ff option says not to complain if this is a login shell; just suspend anyway. The return status is 0 unless the shell is a login shell and --ff is not supplied, or if job control is not enabled. tteesstt _e_x_p_r [[ _e_x_p_r ]] Return a status of 0 (true) or 1 (false) depending on the evaluation of the conditional expression _e_x_p_r. Expressions may be unary or binary. Unary expressions are often used to examine the status of a file. There are string operators and numeric comparison operators as well. Each operator and operand must be a separate argument. --bb _f_i_l_e True if _f_i_l_e exists and is block special. --cc _f_i_l_e True if _f_i_l_e exists and is character spe- cial. --dd _f_i_l_e True if _f_i_l_e exists and is a directory. --ee _f_i_l_e True if _f_i_l_e exists. --ff _f_i_l_e True if _f_i_l_e exists and is a regular file. --gg _f_i_l_e True if _f_i_l_e exists and is set-group-id. --kk _f_i_l_e True if _f_i_l_e has its ``sticky'' bit set. --LL _f_i_l_e True if _f_i_l_e exists and is a symbolic link. --pp _f_i_l_e True if _f_i_l_e exists and is a named pipe. --rr _f_i_l_e True if _f_i_l_e exists and is readable. --ss _f_i_l_e True if _f_i_l_e exists and has a size greater than zero. --SS _f_i_l_e True if _f_i_l_e exists and is a socket. --tt _f_d True if _f_d is opened on a terminal. --uu _f_i_l_e True if _f_i_l_e exists and its set-user-id bit is set. --ww _f_i_l_e True if _f_i_l_e exists and is writable. --xx _f_i_l_e True if _f_i_l_e exists and is executable. --OO _f_i_l_e True if _f_i_l_e exists and is owned by the effective user id. --GG _f_i_l_e True if _f_i_l_e exists and is owned by the GNU 1993 August 9 48 BASH(1) BASH(1) effective group id. _f_i_l_e_1 -nntt _f_i_l_e_2 True if _f_i_l_e_1 is newer (according to modifi- cation date) than _f_i_l_e_2. _f_i_l_e_1 -oott _f_i_l_e_2 True if _f_i_l_e_1 is older than file2. _f_i_l_e_1 --eeff _f_i_l_e True if _f_i_l_e_1 and _f_i_l_e_2 have the same device and inode numbers. --zz _s_t_r_i_n_g True if the length of _s_t_r_i_n_g is zero. --nn _s_t_r_i_n_g _s_t_r_i_n_g True if the length of _s_t_r_i_n_g is non-zero. _s_t_r_i_n_g_1 == _s_t_r_i_n_g_2 True if the strings are equal. _s_t_r_i_n_g_1 !!== _s_t_r_i_n_g_2 True if the strings are not equal. !! _e_x_p_r True if _e_x_p_r is false. _e_x_p_r_1 -aa _e_x_p_r_2 True if both _e_x_p_r_1 AND _e_x_p_r_2 are true. _e_x_p_r_1 -oo _e_x_p_r_2 True if either _e_x_p_r_1 OR _e_x_p_r_2 is true. _a_r_g_1 OOPP _a_r_g_2 OOPP is one of --eeqq, --nnee, --lltt, --llee, --ggtt, or --ggee. These arithmetic binary operators return true if _a_r_g_1 is equal, not-equal, less-than, less-than-or-equal, greater-than, or greater-than-or-equal than _a_r_g_2, respec- tively. _A_r_g_1 and _a_r_g_2 may be positive inte- gers, negative integers, or the special expression --ll _s_t_r_i_n_g, which evaluates to the length of _s_t_r_i_n_g. ttiimmeess Print the accumulated user and system times for the shell and for processes run from the shell. The return status is 0. ttrraapp [_a_r_g] [_s_i_g_s_p_e_c] The command _a_r_g is to be read and executed when the shell receives signal(s) _s_i_g_s_p_e_c. If _a_r_g is absent or --, all specified signals are are reset to their original values (the values they had upon entrance to the shell). If _a_r_g is the null string this sig- nal is ignored by the shell and by the commands it invokes. _s_i_g_s_p_e_c is either a signal name in , or a signal number. If _s_i_g_s_p_e_c is EEXXIITT (0) the command _a_r_g is executed on exit from the shell. With no arguments, ttrraapp prints the list of commands associated with each signal number. The --ll option causes the shell to print a list of signal names and their corresponding numbers. An argument of ---- disables option checking for the rest of the argu- ments. Signals ignored upon entry to the shell cannot be trapped or reset. Trapped signals are GNU 1993 August 9 49 BASH(1) BASH(1) reset to their original values in a child process when it is created. The return status is false if either the trap name or number is invalid; other- wise ttrraapp returns true. ttyyppee [--aallll] [--ttyyppee | --ppaatthh] _n_a_m_e [_n_a_m_e ...] With no options, indicate how each _n_a_m_e would be interpreted if used as a command name. If the --ttyyppee flag is used, ttyyppee prints a phrase which is one of _a_l_i_a_s, _k_e_y_w_o_r_d, _f_u_n_c_t_i_o_n, _b_u_i_l_t_i_n, or _f_i_l_e if _n_a_m_e is an alias, shell reserved word, function, builtin, or disk file, respectively. If the name is not found, then nothing is printed, and an exit status of false is returned. If the --ppaatthh flag is used, ttyyppee either returns the name of the disk file that would be executed if _n_a_m_e were specified as a command name, or nothing if --ttyyppee would not return _f_i_l_e. If a command is hashed, --ppaatthh prints the hashed value, not necessarily the file that appears first in PPAATTHH. If the --aallll flag is used, ttyyppee prints all of the places that contain an executable named _n_a_m_e. This includes aliases and functions, if and only if the --ppaatthh flag is not also used. The table of hashed commands is not consulted when using --aallll. ttyyppee accepts --aa, --tt, and --pp in place of --aallll, --ttyyppee, and --ppaatthh, respectively. An argu- ment of ---- disables option checking for the rest of the arguments. ttyyppee returns true if any of the arguments are found, false if none are found. uulliimmiitt [--SSHHaaccddffmmssttppnn [_l_i_m_i_t]] UUlliimmiitt provides control over the resources avail- able to the shell and to processes started by it, on systems that allow such control. The value of _l_i_m_i_t can be a number in the unit specified for the resource, or the value uunnlliimmiitteedd. The HH and SS options specify that the hard or soft limit is set for the given resource. A hard limit cannot be increased once it is set; a soft limit may be increased up to the value of the hard limit. If neither HH nor SS is specified, the command applies to the soft limit. If _l_i_m_i_t is omitted, the cur- rent value of the soft limit of the resource is printed, unless the HH option is given. When more than one resource is specified, the limit name and unit is printed before the value. Other options are interpreted as follows: --aa all current limits are reported --cc the maximum size of core files created --dd the maximum size of a process's data segment --ff the maximum size of files created by the shell --mm the maximum resident set size --ss the maximum stack size GNU 1993 August 9 50 BASH(1) BASH(1) --tt the maximum amount of cpu time in seconds --pp the pipe size in 512-byte blocks (this may not be set) --nn the maximum number of open file descriptors (most systems do not allow this value to be set, only displayed) --uu the maximum number of processes available to a single user --vv The maximum amount of virtual memory avail- able to the shell An argument of ---- disables option checking for the rest of the arguments. If _l_i_m_i_t is given, it is the new value of the specified resource (the --aa option is display only). If no option is given, then --ff is assumed. Values are in 1024-byte incre- ments, except for --tt, which is in seconds, and --pp, which is in units of 512-byte blocks. The return status is 0 unless an illegal option is encoun- tered, a non-numeric argument other than uunnlliimmiitteedd is supplied as _l_i_m_i_t, or an error occurs while set- ting a new limit. uummaasskk [--SS] [_m_o_d_e] The user file-creation mask is set to _m_o_d_e. If _m_o_d_e begins with a digit, it is interpreted as an octal number; otherwise it is interpreted as a sym- bolic mode mask similar to that accepted by _c_h_m_o_d(1). If _m_o_d_e is omitted, or if the --SS option is supplied, the current value of the mask is printed. The --SS option causes the mask to be printed in symbolic form; the default output is an octal number. An argument of ---- disables option checking for the rest of the arguments. The return status is 0 if the mode was successfully changed or if no _m_o_d_e argument was supplied, and false other- wise. uunnaalliiaass [_n_a_m_e ...] Remove _n_a_m_es from the list of defined aliases. The return value is true unless a supplied _n_a_m_e is not a defined alias. uunnsseett [-ffvv] [_n_a_m_e ...] For each _n_a_m_e, remove the corresponding variable or, given the --ff option, function. An argument of ---- disables option checking for the rest of the arguments. Note that PPAATTHH, IIFFSS, PPPPIIDD, PPSS11, PPSS22, UUIIDD, and EEUUIIDD cannot be unset. If any of RRAANNDDOOMM, SSEECCOONNDDSS, or LLIINNEENNOO are unset, they lose their spe- cial properties, even if they are subsequently reset. The exit status is true unless a _n_a_m_e does not exist or is non-unsettable. GNU 1993 August 9 51 BASH(1) BASH(1) wwaaiitt [_n] Wait for the specified process and return its ter- mination status. _n may be a process ID or a job specification; if a job spec is given, all pro- cesses in that job's pipeline are waited for. If _n is not given, all currently active child processes are waited for, and the return status is zero. If _n specifies a non-existant process or job, the return status is 127. Otherwise, the return status is the exit status of the last process or job waited for. IINNVVOOCCAATTIIOONN A _l_o_g_i_n _s_h_e_l_l is one whose first character of argument zero is a --, or one started with the --llooggiinn flag. An _i_n_t_e_r_a_c_t_i_v_e shell is one whose standard input and out- put are both connected to terminals (as determined by _i_s_a_t_t_y(3)), or one started with the --ii option. PPSS11 is set and $$-- includes ii if bbaasshh is interactive, allowing a shell script or a startup file to test this state. Login shells: On login: if _/_e_t_c_/_p_r_o_f_i_l_e exists, source it. if _~_/_._b_a_s_h___p_r_o_f_i_l_e exists, source it, else if _~_/_._b_a_s_h___l_o_g_i_n exists, source it, else if _~_/_._p_r_o_f_i_l_e exists, source it. On exit: if _~_/_._b_a_s_h___l_o_g_o_u_t exists, source it. Non-login interactive shells: On startup: if _~_/_._b_a_s_h_r_c exists, source it. Non-interactive shells: On startup: if the environment variable EENNVV is non-null, expand it and source the file it names, as if the command if [ "$ENV" ]; then . $ENV; fi had been executed, but do not use PPAATTHH to search for the pathname. SSEEEE AALLSSOO _T_h_e _G_n_u _R_e_a_d_l_i_n_e _L_i_b_r_a_r_y, Brian Fox _T_h_e _G_n_u _H_i_s_t_o_r_y _L_i_b_r_a_r_y, Brian Fox _A _S_y_s_t_e_m _V _C_o_m_p_a_t_i_b_l_e _I_m_p_l_e_m_e_n_t_a_t_i_o_n _o_f _4_._2_B_S_D _J_o_b _C_o_n_t_r_o_l, David Lennert _P_o_r_t_a_b_l_e _O_p_e_r_a_t_i_n_g _S_y_s_t_e_m _I_n_t_e_r_f_a_c_e _(_P_O_S_I_X_) _P_a_r_t _2_: _S_h_e_l_l _a_n_d _U_t_i_l_i_t_i_e_s, IEEE GNU 1993 August 9 52 BASH(1) BASH(1) _H_o_w _t_o _w_e_a_r _w_e_i_r_d _p_a_n_t_s _f_o_r _f_u_n _a_n_d _p_r_o_f_i_t, Brian Fox _s_h(1), _k_s_h(1), _c_s_h(1) _e_m_a_c_s(1), _v_i(1) FFIILLEESS _/_b_i_n_/_b_a_s_h The bbaasshh executable _/_e_t_c_/_p_r_o_f_i_l_e The systemwide initialization file, executed for login shells _~_/_._b_a_s_h___p_r_o_f_i_l_e The personal initialization file, executed for login shells _~_/_._b_a_s_h_r_c The individual per-interactive-shell startup file _~_/_._i_n_p_u_t_r_c Individual _R_e_a_d_l_i_n_e initialization file AAUUTTHHOORRSS Brian Fox, Free Software Foundation (primary author) bfox@ai.MIT.Edu Chet Ramey, Case Western Reserve University chet@ins.CWRU.Edu BBUUGG RREEPPOORRTTSS If you find a bug in bbaasshh,, you should report it. But first, you should make sure that it really is a bug, and that it appears in the latest version of bbaasshh that you have. Once you have determined that a bug actually exists, mail a bug report to _b_a_s_h_-_m_a_i_n_t_a_i_n_e_r_s@_a_i_._M_I_T_._E_d_u. If you have a fix, you are welcome to mail that as well! Suggestions and `philosophical' bug reports may be mailed to _b_u_g_- _b_a_s_h@_a_i_._M_I_T_._E_d_u or posted to the Usenet newsgroup ggnnuu..bbaasshh..bbuugg. ALL bug reports should include: The version number of bbaasshh The hardware and operating system The compiler used to compile A description of the bug behaviour A short script or `recipe' which exercises the bug Comments and bug reports concerning this manual page should be directed to _c_h_e_t_@_i_n_s_._C_W_R_U_._E_d_u. BBUUGGSS It's too big and too slow. There are some subtle differences between bbaasshh and GNU 1993 August 9 53 BASH(1) BASH(1) traditional versions of sshh, mostly because of the PPOOSSIIXX specification. Aliases are confusing in some uses. GNU 1993 August 9 54 .