trc.1 - plan9port - [fork] Plan 9 from user space
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trc.1 (20266B)
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1 .TH RC 1
2 .SH NAME
3 rc, cd, eval, exec, exit, flag, rfork, shift, wait, whatis, ., ~ \- command language
4 .SH SYNOPSIS
5 .B rc
6 [
7 .B -srdiIlxepvV
8 ]
9 [
10 .B -c command
11 ]
12 [
13 .I file
14 [
15 .I arg ...
16 ]]
17 .SH DESCRIPTION
18 .I Rc
19 is the Plan 9 shell.
20 It executes command lines read from a terminal or a file or, with the
21 .B -c
22 flag, from
23 .I rc's
24 argument list.
25 .SS Command Lines
26 A command line is a sequence of commands, separated by ampersands or semicolons
27 .RB ( &
28 or
29 .BR ; ),
30 terminated by a newline.
31 The commands are executed in sequence
32 from left to right.
33 .I Rc
34 does not wait for a command followed by
35 .B &
36 to finish executing before starting
37 the following command.
38 Whenever a command followed by
39 .B &
40 is executed, its process id is assigned to the
41 .I rc
42 variable
43 .BR $apid .
44 Whenever a command
45 .I not
46 followed by
47 .B &
48 exits or is terminated, the
49 .I rc
50 variable
51 .B $status
52 gets the process's wait message (see
53 .MR wait (3) );
54 it will be the null string if the command was successful.
55 .PP
56 A long command line may be continued on subsequent lines by typing
57 a backslash
58 .RB ( \e )
59 followed by a newline.
60 This sequence is treated as though it were a blank.
61 Backslash is not otherwise a special character.
62 .PP
63 A number-sign
64 .RB ( # )
65 and any following characters up to (but not including) the next newline
66 are ignored, except in quotation marks.
67 .SS Simple Commands
68 A simple command is a sequence of arguments interspersed with I/O redirections.
69 If the first argument is the name of an
70 .I rc
71 function or of one of
72 .I rc's
73 built-in commands, it is executed by
74 .IR rc .
75 Otherwise if the name starts with a slash
76 .RB ( / ),
77 it must be the path name of the program to be executed.
78 Names containing no initial slash are searched for in
79 a list of directory names stored in
80 .BR $path .
81 The first executable file of the given name found
82 in a directory in
83 .B $path
84 is the program to be executed.
85 To be executable, the user must have execute permission (see
86 .MR stat (3) )
87 and the file must be either an executable binary
88 for the current machine's CPU type, or a shell script.
89 Shell scripts begin with a line containing the full path name of a shell
90 (usually
91 .BR /bin/rc ),
92 prefixed by
93 .LR #! .
94 .PP
95 The first word of a simple command cannot be a keyword unless it is
96 quoted or otherwise disguised.
97 The keywords are
98 .EX
99 for in while if not switch fn ~ ! @
100 .EE
101 .SS Arguments and Variables
102 A number of constructions may be used where
103 .I rc's
104 syntax requires an argument to appear.
105 In many cases a construction's
106 value will be a list of arguments rather than a single string.
107 .PP
108 The simplest kind of argument is the unquoted word:
109 a sequence of one or more characters none of which is a blank, tab,
110 newline, or any of the following:
111 .EX
112 # ; & | ^ $ ` ' { } ( ) < >
113 .EE
114 An unquoted word that contains any of the characters
115 .B *
116 .B ?
117 .B [
118 is a pattern for matching against file names.
119 The character
120 .B *
121 matches any sequence of characters,
122 .B ?
123 matches any single character, and
124 .BI [ class ]
125 matches any character in the
126 .IR class .
127 If the first character of
128 .I class
129 is
130 .BR ~ ,
131 the class is complemented.
132 The
133 .I class
134 may also contain pairs of characters separated by
135 .BR - ,
136 standing for all characters lexically between the two.
137 The character
138 .B /
139 must appear explicitly in a pattern, as must the
140 first character of the path name components
141 .B .
142 and
143 .BR .. .
144 A pattern is replaced by a list of arguments, one for each path name matched,
145 except that a pattern matching no names is not replaced by the empty list,
146 but rather stands for itself.
147 Pattern matching is done after all other
148 operations.
149 Thus,
150 .EX
151 x=/tmp echo $x^/*.c
152 .EE
153 matches
154 .BR /tmp/*.c ,
155 rather than matching
156 .B "/*.c
157 and then prefixing
158 .BR /tmp .
159 .PP
160 A quoted word is a sequence of characters surrounded by single quotes
161 .RB ( ' ).
162 A single quote is represented in a quoted word by a pair of quotes
163 .RB ( '' ).
164 .PP
165 Each of the following is an argument.
166 .PD 0
167 .HP
168 .BI ( arguments )
169 .br
170 The value of a sequence of arguments enclosed in parentheses is
171 a list comprising the members of each element of the sequence.
172 Argument lists have no recursive structure, although their syntax may
173 suggest it.
174 The following are entirely equivalent:
175 .EX
176 echo hi there everybody
177 ((echo) (hi there) everybody)
178 .EE
179 .HP
180 .BI $ argument
181 .HP
182 .BI $ argument ( subscript )
183 .br
184 The
185 .I argument
186 after the
187 .B $
188 is the name of a variable whose value is substituted.
189 Multiple levels
190 of indirection are possible, but of questionable utility.
191 Variable values
192 are lists of strings.
193 If
194 .I argument
195 is a number
196 .IR n ,
197 the value is the
198 .IR n th
199 element of
200 .BR $* ,
201 unless
202 .B $*
203 doesn't have
204 .I n
205 elements, in which case the value is empty.
206 If
207 .I argument
208 is followed by a parenthesized list of subscripts, the
209 value substituted is a list composed of the requested elements (origin 1).
210 The parenthesis must follow the variable name with no spaces.
211 Subscripts can also take the form
212 .IB m - n
213 or
214 .IB m -
215 to indicate a sequence of elements.
216 Assignments to variables are described below.
217 .HP
218 .BI $# argument
219 .br
220 The value is the number of elements in the named variable.
221 A variable
222 never assigned a value has zero elements.
223 .HP
224 $"\c
225 .I argument
226 .br
227 The value is a single string containing the components of the named variable
228 separated by spaces. A variable with zero elements yields the empty string.
229 .HP
230 .BI `{ command }
231 .br
232 .I rc
233 executes the
234 .I command
235 and reads its standard output, splitting it into a list of arguments,
236 using characters in
237 .B $ifs
238 as separators.
239 If
240 .B $ifs
241 is not otherwise set, its value is
242 .BR "'\ \et\en'" .
243 .HP
244 .BI <{ command }
245 .HP
246 .BI >{ command }
247 .br
248 The
249 .I command
250 is executed asynchronously with its standard output or standard input
251 connected to a pipe.
252 The value of the argument is the name of a file
253 referring to the other end of the pipe.
254 This allows the construction of
255 non-linear pipelines.
256 For example, the following runs two commands
257 .B old
258 and
259 .B new
260 and uses
261 .B cmp
262 to compare their outputs
263 .EX
264 cmp <{old} <{new}
265 .EE
266 .HP
267 .BI <>{ command }
268 .br
269 The
270 .I command
271 is executed asynchronously with its standard input and
272 output each connected to a pipe. The value of the argument
273 is a pair of file names referring to the two other ends
274 of the pipes, in the order corresponding to the symbols
275 .B <
276 and
277 .B >
278 (first the pipe connected to the command's standard output,
279 then the pipe connected to its standard input).
280 .HP
281 .IB argument ^ argument
282 .br
283 The
284 .B ^
285 operator concatenates its two operands.
286 If the two operands
287 have the same number of components, they are concatenated pairwise.
288 If not,
289 then one operand must have one component, and the other must be non-empty,
290 and concatenation is distributive.
291 .PD
292 .SS Free Carets
293 .I Rc
294 will insert the
295 .B ^
296 operator automatically between words that are not separated by white space.
297 Thus
298 .IP
299 .B cc -$flags $stem.c
300 .LP
301 is equivalent to
302 .IP
303 .B cc -^$flags $stem^.c
304 .SS I/O Redirections
305 The sequence
306 .BI > file
307 redirects the standard output file (file descriptor 1, normally the
308 terminal) to the named
309 .IR file ;
310 .BI >> file
311 appends standard output to the file.
312 The standard input file (file descriptor 0, also normally the terminal)
313 may be redirected from a file by the sequence
314 .BI < file \f1,
315 or from an inline `here document'
316 by the sequence
317 .BI << eof-marker\f1.
318 The contents of a here document are lines of text taken from the command
319 input stream up to a line containing nothing but the
320 .IR eof-marker ,
321 which may be either a quoted or unquoted word.
322 If
323 .I eof-marker
324 is unquoted, variable names of the form
325 .BI $ word
326 have their values substituted from
327 .I rc's
328 environment.
329 If
330 .BI $ word
331 is followed by a caret
332 .RB ( ^ ),
333 the caret is deleted.
334 If
335 .I eof-marker
336 is quoted, no substitution occurs.
337 .PP
338 Redirections may be applied to a file-descriptor other than standard input
339 or output by qualifying the redirection operator
340 with a number in square brackets.
341 For example, the diagnostic output (file descriptor 2)
342 may be redirected by writing
343 .BR "cc junk.c >[2]junk" .
344 .PP
345 A file descriptor may be redirected to an already open descriptor by writing
346 .BI >[ fd0 = fd1 ]
347 or
348 .BI <[ fd0 = fd1 ]\f1.
349 .I Fd1
350 is a previously opened file descriptor and
351 .I fd0
352 becomes a new copy (in the sense of
353 .MR dup (3) )
354 of it.
355 A file descriptor may be closed by writing
356 .BI >[ fd0 =]
357 or
358 .BI <[ fd0 =]\f1.
359 .PP
360 Redirections are executed from left to right.
361 Therefore,
362 .B cc junk.c >/dev/null >[2=1]
363 and
364 .B cc junk.c >[2=1] >/dev/null
365 have different effects: the first puts standard output in
366 .BR /dev/null
367 and then puts diagnostic output in the same place, where the second
368 directs diagnostic output to the terminal and sends standard output to
369 .BR /dev/null .
370 .SS Compound Commands
371 A pair of commands separated by a pipe operator
372 .RB ( | )
373 is a command.
374 The standard output of the left command is sent through a pipe
375 to the standard input of the right command.
376 The pipe operator may be decorated
377 to use different file descriptors.
378 .BI |[ fd ]
379 connects the output end of the pipe to file descriptor
380 .I fd
381 rather than 1.
382 .BI |[ fd0 = fd1 ]
383 connects output to
384 .I fd1
385 of the left command and input to
386 .I fd0
387 of the right command.
388 .PP
389 A pair of commands separated by
390 .B &&
391 or
392 .B ||
393 is a command.
394 In either case, the left command is executed and its exit status examined.
395 If the operator is
396 .B &&
397 the right command is executed if the left command's status is null.
398 .B ||
399 causes the right command to be executed if the left command's status is non-null.
400 .PP
401 The exit status of a command may be inverted (non-null is changed to null, null
402 is changed to non-null) by preceding it with a
403 .BR ! .
404 .PP
405 The
406 .B |
407 operator has highest precedence, and is left-associative (i.e. binds tighter
408 to the left than the right).
409 .B !
410 has intermediate precedence, and
411 .B &&
412 and
413 .B ||
414 have the lowest precedence.
415 .PP
416 The unary
417 .B @
418 operator, with precedence equal to
419 .BR ! ,
420 causes its operand to be executed in a subshell.
421 .PP
422 Each of the following is a command.
423 .PD 0
424 .HP
425 .B if (
426 .I list
427 .B )
428 .I command
429 .br
430 A
431 .I list
432 is a sequence of commands, separated by
433 .BR & ,
434 .BR ; ,
435 or newline.
436 It is executed and
437 if its exit status is null, the
438 .I command
439 is executed.
440 .HP
441 .B if not
442 .I command
443 .br
444 The immediately preceding command must have been
445 .BI if( list )
446 .IR command .
447 If its condition was non-zero, the
448 .I command
449 is executed.
450 .HP
451 .BI for( name
452 .B in
453 .IB arguments )
454 .I command
455 .HP
456 .BI for( name )
457 .I command
458 .br
459 The
460 .I command
461 is executed once for each
462 .IR argument
463 with that argument assigned to
464 .IR name .
465 If the argument list is omitted,
466 .B $*
467 is used.
468 .HP
469 .BI while( list )
470 .I command
471 .br
472 The
473 .I list
474 is executed repeatedly until its exit status is non-null.
475 Each time it returns null status, the
476 .I command
477 is executed.
478 An empty
479 .I list
480 is taken to give null status.
481 .HP
482 .BI "switch(" argument "){" list }
483 .br
484 The
485 .IR list
486 is searched for simple commands beginning with the word
487 .BR case .
488 (The search is only at the `top level' of the
489 .IR list .
490 That is,
491 .B cases
492 in nested constructs are not found.)
493 .I Argument
494 is matched against each word following
495 .B case
496 using the pattern-matching algorithm described above, except that
497 .B /
498 and the first characters of
499 .B .
500 and
501 .B ..
502 need not be matched explicitly.
503 When a match is found, commands in the list are executed up to the next
504 following
505 .B case
506 command (at the top level) or the closing brace.
507 .HP
508 .BI { list }
509 .br
510 Braces serve to alter the grouping of commands implied by operator
511 priorities.
512 The
513 .I body
514 is a sequence of commands separated by
515 .BR & ,
516 .BR ; ,
517 or newline.
518 .HP
519 .BI "fn " name { list }
520 .HP
521 .BI "fn " name
522 .br
523 The first form defines a function with the given
524 .IR name .
525 Subsequently, whenever a command whose first argument is
526 .I name
527 is encountered, the current value of
528 the remainder of the command's argument list will be assigned to
529 .BR $* ,
530 after saving its current value, and
531 .I rc
532 will execute the
533 .IR list .
534 The second form removes
535 .IR name 's
536 function definition.
537 .HP
538 .BI "fn " note { list }
539 .br
540 .HP
541 .BI "fn " note
542 .br
543 A function with a special name will be called when
544 .I rc
545 receives a corresponding note; see
546 .MR notify (3) .
547 The valid note names (and corresponding notes) are
548 .B sighup
549 .RB ( hangup ),
550 .B sigint
551 .RB ( interrupt ),
552 .BR sigalrm
553 .RB ( alarm ),
554 and
555 .B sigfpe
556 (floating point trap).
557 By default
558 .I rc
559 exits on receiving any signal, except when run interactively,
560 in which case interrupts and quits normally cause
561 .I rc
562 to stop whatever it's doing and start reading a new command.
563 The second form causes
564 .I rc
565 to handle a signal in the default manner.
566 .I Rc
567 recognizes an artificial note,
568 .BR sigexit ,
569 which occurs when
570 .I rc
571 is about to finish executing.
572 .HP
573 .IB name = "argument command"
574 .br
575 Any command may be preceded by a sequence of assignments
576 interspersed with redirections.
577 The assignments remain in effect until the end of the command, unless
578 the command is empty (i.e. the assignments stand alone), in which case
579 they are effective until rescinded by later assignments.
580 .PD
581 .SS Built-in Commands
582 These commands are executed internally by
583 .IR rc ,
584 usually because their execution changes or depends on
585 .IR rc 's
586 internal state.
587 .PD 0
588 .HP
589 .BI . " file ..."
590 .br
591 Execute commands from
592 .IR file .
593 .B $*
594 is set for the duration to the remainder of the argument list following
595 .IR file .
596 .I File
597 is searched for using
598 .BR $path .
599 .HP
600 .BI builtin " command ..."
601 .br
602 Execute
603 .I command
604 as usual except that any function named
605 .I command
606 is ignored in favor of the built-in meaning.
607 .HP
608 .BI "cd [" dir "]"
609 .br
610 Change the current directory to
611 .IR dir .
612 The default argument is
613 .BR $home .
614 .I dir
615 is searched for in each of the directories mentioned in
616 .BR $cdpath .
617 .HP
618 .BI "eval [" "arg ..." "]"
619 .br
620 The arguments are concatenated separated by spaces into a single string,
621 read as input to
622 .IR rc ,
623 and executed.
624 .HP
625 .BI "exec [" "command ..." "]"
626 .br
627 This instance of
628 .I rc
629 replaces itself with the given (non-built-in)
630 .IR command .
631 .HP
632 .BI "flag " f " [+-]"
633 .br
634 Either set
635 .RB ( + ),
636 clear
637 .RB ( - ),
638 or test (neither
639 .B +
640 nor
641 .BR - )
642 the flag
643 .IR f ,
644 where
645 .I f
646 is a single character, one of the command line flags (see Invocation, below).
647 .HP
648 .BI "exit [" status "]"
649 .br
650 Exit with the given exit status.
651 If none is given, the current value of
652 .B $status
653 is used.
654 .HP
655 .BR "rfork " [ nNeEsfFm ]
656 .br
657 Become a new process group using
658 .BI rfork( flags )
659 where
660 .I flags
661 is composed of the bitwise OR of the
662 .B rfork
663 flags specified by the option letters
664 (see
665 .MR fork (2) ).
666 If no
667 .I flags
668 are given, they default to
669 .BR ens .
670 The
671 .I flags
672 and their meanings are:
673 .B n
674 is
675 .BR RFNAMEG ;
676 .B N
677 is
678 .BR RFCNAMEG ;
679 .B e
680 is
681 .BR RFENVG ;
682 .B E
683 is
684 .BR RFCENVG ;
685 .B s
686 is
687 .BR RFNOTEG ;
688 .B f
689 is
690 .BR RFFDG ;
691 .B F
692 is
693 .BR RFCFDG ;
694 and
695 .B m
696 is
697 .BR RFNOMNT .
698 .HP
699 .BI "shift [" n "]"
700 .br
701 Delete the first
702 .IR n
703 (default 1)
704 elements of
705 .BR $* .
706 .HP
707 .BI "wait [" pid "]"
708 .br
709 Wait for the process with the given
710 .I pid
711 to exit.
712 If no
713 .I pid
714 is given, all outstanding processes are waited for.
715 .HP
716 .BI whatis " name ..."
717 .br
718 Print the value of each
719 .I name
720 in a form suitable for input to
721 .IR rc .
722 The output is
723 an assignment to any variable,
724 the definition of any function,
725 a call to
726 .B builtin
727 for any built-in command, or
728 the completed pathname of any executable file.
729 .HP
730 .BI ~ " subject pattern ..."
731 .br
732 The
733 .I subject
734 is matched against each
735 .I pattern
736 in sequence.
737 If it matches any pattern,
738 .B $status
739 is set to zero.
740 Otherwise,
741 .B $status
742 is set to one.
743 Patterns are the same as for file name matching, except that
744 .B /
745 and the first character of
746 .B .
747 and
748 .B ..
749 need not be matched explicitly.
750 The
751 .I patterns
752 are not subjected to
753 file name matching before the
754 .B ~
755 command is executed, so they need not be enclosed in quotation marks.
756 .PD
757 .SS Environment
758 The
759 .I environment
760 is a list of strings made available to executing binaries by the
761 kernel.
762 .I Rc
763 creates an environment entry for each variable whose value is non-empty,
764 and for each function.
765 The string for a variable entry has the variable's name followed by
766 .B =
767 and its value.
768 If the value has more than one component, these
769 are separated by SOH (001)
770 characters.
771 The string for a function is just the
772 .I rc
773 input that defines the function.
774 The name of a function in the environment is the function name
775 preceded by
776 .LR fn# .
777 .PP
778 When
779 .I rc
780 starts executing it reads variable and function definitions from its
781 environment.
782 .SS Special Variables
783 The following variables are set or used by
784 .IR rc .
785 .PD 0
786 .TP \w'\fL$promptXX'u
787 .B $*
788 Set to
789 .IR rc 's
790 argument list during initialization.
791 Whenever a
792 .B .
793 command or a function is executed, the current value is saved and
794 .B $*
795 receives the new argument list.
796 The saved value is restored on completion of the
797 .B .
798 or function.
799 .TP
800 .B $apid
801 Whenever a process is started asynchronously with
802 .BR & ,
803 .B $apid
804 is set to its process id.
805 .TP
806 .B $home
807 The default directory for
808 .BR cd .
809 Defaults to
810 .B $HOME
811 or else
812 .LR / .
813 .TP
814 .B $ifs
815 The input field separators used in backquote substitutions.
816 If
817 .B $ifs
818 is not set in
819 .IR rc 's
820 environment, it is initialized to blank, tab and newline.
821 .TP
822 .B $path
823 The search path used to find commands and input files
824 for the
825 .B .
826 command.
827 If not set in the environment, it is initialized by
828 parsing the
829 .B $PATH
830 variable
831 (as in
832 .MR sh (1) )
833 or by
834 .BR "path=(.\ /bin)" .
835 The variables
836 .B $path
837 and
838 .B $PATH
839 are maintained together: changes to one will be reflected in the other.
840 .\" Its use is discouraged; instead use
841 .\" .IR bind (1)
842 .\" to build a
843 .\" .B /bin
844 .\" containing what's needed.
845 .TP
846 .B $pid
847 Set during initialization to
848 .IR rc 's
849 process id.
850 .TP
851 .B $prompt
852 When
853 .I rc
854 is run interactively, the first component of
855 .B $prompt
856 is printed before reading each command.
857 The second component is printed whenever a newline is typed and more lines
858 are required to complete the command.
859 If not set in the environment, it is initialized by
860 .BR "prompt=('%\ '\ '\ ')" .
861 .TP
862 .B $status
863 Set to the wait message of the last-executed program.
864 (unless started with
865 .BR &).
866 .B !
867 and
868 .B ~
869 also change
870 .BR $status .
871 Its value is used to control execution in
872 .BR && ,
873 .BR || ,
874 .B if
875 and
876 .B while
877 commands.
878 When
879 .I rc
880 exits at end-of-file of its input or on executing an
881 .B exit
882 command with no argument,
883 .B $status
884 is its exit status.
885 .PD
886 .SS Invocation
887 If
888 .I rc
889 is started with no arguments it reads commands from standard input.
890 Otherwise its first non-flag argument is the name of a file from which
891 to read commands (but see
892 .B -c
893 below).
894 Subsequent arguments become the initial value of
895 .BR $* .
896 .I Rc
897 accepts the following command-line flags.
898 .PD 0
899 .TP \w'\fL-c\ \fIstring\fLXX'u
900 .BI -c " string"
901 Commands are read from
902 .IR string .
903 .TP
904 .B -s
905 Print out exit status after any command where the status is non-null.
906 .TP
907 .B -e
908 Exit if
909 .B $status
910 is non-null after executing a simple command.
911 .TP
912 .B -i
913 If
914 .B -i
915 is present, or
916 .I rc
917 is given no arguments and its standard input is a terminal,
918 it runs interactively.
919 Commands are prompted for using
920 .BR $prompt .
921 .TP
922 .B -I
923 Makes sure
924 .I rc
925 is not run interactively.
926 .TP
927 .B -l
928 If
929 .B -l
930 is given or the first character of argument zero is
931 .BR - ,
932 .I rc
933 reads commands from
934 .BR $home/lib/profile ,
935 if it exists, before reading its normal input.
936 .TP
937 .B -p
938 A no-op.
939 .TP
940 .B -d
941 A no-op.
942 .TP
943 .B -v
944 Echo input on file descriptor 2 as it is read.
945 .TP
946 .B -x
947 Print each simple command before executing it.
948 .TP
949 .B -r
950 Print debugging information (internal form of commands
951 as they are executed).
952 .PD
953 .SH SOURCE
954 .B \*9/src/cmd/rc
955 .SH "SEE ALSO"
956 Tom Duff,
957 ``Rc \- The Plan 9 Shell''.
958 .SH BUGS
959 There should be a way to match patterns against whole lists rather than
960 just single strings.
961 .PP
962 Using
963 .B ~
964 to check the value of
965 .B $status
966 changes
967 .BR $status .
968 .PP
969 Functions that use here documents don't work.
970 .PP
971 The
972 .BI <{ command }
973 syntax depends on the underlying operating system
974 providing a file descriptor device tree at
975 .BR /dev/fd .
976 .PP
977 Some FreeBSD installations
978 does not provide file descriptors greater than 2
979 in
980 .BR /dev/fd .
981 To fix this, add
982 .IP
983 .EX
984 /fdescfs /dev/fd fdescfs rw 0 0
985 .EE
986 .LP
987 to
988 .BR /etc/fstab ,
989 and then
990 .B mount
991 .BR /dev/fd .
992 (Adding the line to
993 .B fstab
994 ensures causes FreeBSD to mount the file system
995 automatically at boot time.)
996 .PP
997 Some systems require
998 .B \*9/bin/rc
999 to be listed in
1000 .B /etc/shells
1001 before it can be used as a login shell.