3 rc, cd, eval, exec, exit, flag, rfork, shift, wait, whatis, ., ~ \- command language
20 It executes command lines read from a terminal or a file or, with the
26 A command line is a sequence of commands, separated by ampersands or semicolons
30 terminated by a newline.
31 The commands are executed in sequence
34 does not wait for a command followed by
36 to finish executing before starting
37 the following command.
38 Whenever a command followed by
40 is executed, its process id is assigned to the
48 exits or is terminated, the
52 gets the process's wait message (see
54 it will be the null string if the command was successful.
56 A long command line may be continued on subsequent lines by typing
59 followed by a newline.
60 This sequence is treated as though it were a blank.
61 Backslash is not otherwise a special character.
65 and any following characters up to (but not including) the next newline
66 are ignored, except in quotation marks.
68 A simple command is a sequence of arguments interspersed with I/O redirections.
69 If the first argument is the name of an
73 built-in commands, it is executed by
75 Otherwise if the name starts with a slash
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
81 The first executable file of the given name found
84 is the program to be executed.
85 To be executable, the user must have execute permission (see
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
95 The first word of a simple command cannot be a keyword unless it is
96 quoted or otherwise disguised.
99 for in while if not switch fn ~ ! @
101 .SS Arguments and Variables
102 A number of constructions may be used where
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.
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:
112 # ; & | ^ $ = ` ' { } ( ) < >
114 An unquoted word that contains any of the characters
118 is a pattern for matching against file names.
121 matches any sequence of characters,
123 matches any single character, and
125 matches any character in the
127 If the first character of
131 the class is complemented.
134 may also contain pairs of characters separated by
136 standing for all characters lexically between the two.
139 must appear explicitly in a pattern, as must the
140 first character of the path name components
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
160 A quoted word is a sequence of characters surrounded by single quotes
162 A single quote is represented in a quoted word by a pair of quotes
165 Each of the following is an argument.
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
174 The following are entirely equivalent:
176 echo hi there everybody
177 ((echo) (hi there) everybody)
182 .BI $ argument ( subscript )
188 is the name of a variable whose value is substituted.
190 of indirection are possible, but of questionable utility.
192 are lists of strings.
205 elements, in which case the value is empty.
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 Assignments to variables are described below.
215 The value is the number of elements in the named variable.
217 never assigned a value has zero elements.
222 The value is a single string containing the components of the named variable
223 separated by spaces. A variable with zero elements yields the empty string.
230 and reads its standard output, splitting it into a list of arguments,
236 is not otherwise set, its value is
245 is executed asynchronously with its standard output or standard input
247 The value of the argument is the name of a file
248 referring to the other end of the pipe.
249 This allows the construction of
250 non-linear pipelines.
251 For example, the following runs two commands
257 to compare their outputs
262 .IB argument ^ argument
266 operator concatenates its two operands.
268 have the same number of components, they are concatenated pairwise.
270 then one operand must have one component, and the other must be non-empty,
271 and concatenation is distributive.
274 In most circumstances,
278 operator automatically between words that are not separated by white space.
283 follows a quoted or unquoted word or an unquoted word follows a quoted word
284 with no intervening blanks or tabs,
287 is inserted between the two.
288 If an unquoted word immediately follows a
290 and contains a character other than an alphanumeric, underscore,
295 is inserted before the first such character.
298 .B cc -$flags $stem.c
302 .B cc -^$flags $stem^.c
306 redirects the standard output file (file descriptor 1, normally the
307 terminal) to the named
310 appends standard output to the file.
311 The standard input file (file descriptor 0, also normally the terminal)
312 may be redirected from a file by the sequence
314 or from an inline `here document'
316 .BI << eof-marker\f1.
317 The contents of a here document are lines of text taken from the command
318 input stream up to a line containing nothing but the
320 which may be either a quoted or unquoted word.
323 is unquoted, variable names of the form
325 have their values substituted from
330 is followed by a caret
332 the caret is deleted.
335 is quoted, no substitution occurs.
337 Redirections may be applied to a file-descriptor other than standard input
338 or output by qualifying the redirection operator
339 with a number in square brackets.
340 For example, the diagnostic output (file descriptor 2)
341 may be redirected by writing
342 .BR "cc junk.c >[2]junk" .
344 A file descriptor may be redirected to an already open descriptor by writing
347 .BI <[ fd0 = fd1 ]\f1.
349 is a previously opened file descriptor and
351 becomes a new copy (in the sense of
354 A file descriptor may be closed by writing
359 Redirections are executed from left to right.
361 .B cc junk.c >/dev/null >[2=1]
363 .B cc junk.c >[2=1] >/dev/null
364 have different effects: the first puts standard output in
366 and then puts diagnostic output in the same place, where the second
367 directs diagnostic output to the terminal and sends standard output to
369 .SS Compound Commands
370 A pair of commands separated by a pipe operator
373 The standard output of the left command is sent through a pipe
374 to the standard input of the right command.
375 The pipe operator may be decorated
376 to use different file descriptors.
378 connects the output end of the pipe to file descriptor
384 of the left command and input to
386 of the right command.
388 A pair of commands separated by
393 In either case, the left command is executed and its exit status examined.
396 the right command is executed if the left command's status is null.
398 causes the right command to be executed if the left command's status is non-null.
400 The exit status of a command may be inverted (non-null is changed to null, null
401 is changed to non-null) by preceding it with a
406 operator has highest precedence, and is left-associative (i.e. binds tighter
407 to the left than the right).
409 has intermediate precedence, and
413 have the lowest precedence.
417 operator, with precedence equal to
419 causes its operand to be executed in a subshell.
421 Each of the following is a command.
431 is a sequence of commands, separated by
436 if its exit status is null, the
443 The immediately preceding command must have been
446 If its condition was non-zero, the
460 is executed once for each
462 with that argument assigned to
464 If the argument list is omitted,
473 is executed repeatedly until its exit status is non-null.
474 Each time it returns null status, the
479 is taken to give null status.
481 .BI "switch(" argument "){" list }
485 is searched for simple commands beginning with the word
487 (The search is only at the `top level' of the
491 in nested constructs are not found.)
493 is matched against each word following
495 using the pattern-matching algorithm described above, except that
497 and the first characters of
501 need not be matched explicitly.
502 When a match is found, commands in the list are executed up to the next
505 command (at the top level) or the closing brace.
509 Braces serve to alter the grouping of commands implied by operator
513 is a sequence of commands separated by
518 .BI "fn " name { list }
522 The first form defines a function with the given
524 Subsequently, whenever a command whose first argument is
526 is encountered, the current value of
527 the remainder of the command's argument list will be assigned to
529 after saving its current value, and
533 The second form removes
537 .BI "fn " note { list }
542 A function with a special name will be called when
544 receives a corresponding note; see
546 The valid note names (and corresponding notes) are
555 (floating point trap).
558 exits on receiving any signal, except when run interactively,
559 in which case interrupts and quits normally cause
561 to stop whatever it's doing and start reading a new command.
562 The second form causes
564 to handle a signal in the default manner.
566 recognizes an artificial note,
570 is about to finish executing.
572 .IB name = "argument command"
574 Any command may be preceded by a sequence of assignments
575 interspersed with redirections.
576 The assignments remain in effect until the end of the command, unless
577 the command is empty (i.e. the assignments stand alone), in which case
578 they are effective until rescinded by later assignments.
580 .SS Built-in Commands
581 These commands are executed internally by
583 usually because their execution changes or depends on
590 Execute commands from
593 is set for the duration to the remainder of the argument list following
596 is searched for using
599 .BI builtin " command ..."
603 as usual except that any function named
605 is ignored in favor of the built-in meaning.
609 Change the current directory to
611 The default argument is
614 is searched for in each of the directories mentioned in
617 .BI "eval [" "arg ..." "]"
619 The arguments are concatenated separated by spaces into a single string,
624 .BI "exec [" "command ..." "]"
628 replaces itself with the given (non-built-in)
631 .BI "flag " f " [+-]"
645 is a single character, one of the command line flags (see Invocation, below).
647 .BI "exit [" status "]"
649 Exit with the given exit status.
650 If none is given, the current value of
654 .BR "rfork " [ nNeEsfFm ]
656 Become a new process group using
660 is composed of the bitwise OR of the
662 flags specified by the option letters
667 are given, they default to
671 and their meanings are:
708 Wait for the process with the given
713 is given, all outstanding processes are waited for.
715 .BI whatis " name ..."
717 Print the value of each
719 in a form suitable for input to
722 an assignment to any variable,
723 the definition of any function,
726 for any built-in command, or
727 the completed pathname of any executable file.
729 .BI ~ " subject pattern ..."
733 is matched against each
736 If it matches any pattern,
742 Patterns are the same as for file name matching, except that
744 and the first character of
748 need not be matched explicitly.
752 file name matching before the
754 command is executed, so they need not be enclosed in quotation marks.
759 is a list of strings made available to executing binaries by the
762 creates an environment entry for each variable whose value is non-empty,
763 and for each function.
764 The string for a variable entry has the variable's name followed by
767 If the value has more than one component, these
768 are separated by SOH (001)
770 The string for a function is just the
772 input that defines the function.
773 The name of a function in the environment is the function name
779 starts executing it reads variable and function definitions from its
781 .SS Special Variables
782 The following variables are set or used by
785 .TP \w'\fL$promptXX'u
789 argument list during initialization.
792 command or a function is executed, the current value is saved and
794 receives the new argument list.
795 The saved value is restored on completion of the
800 Whenever a process is started asynchronously with
803 is set to its process id.
806 The default directory for
810 The input field separators used in backquote substitutions.
815 environment, it is initialized to blank, tab and newline.
818 The search path used to find commands and input files
822 If not set in the environment, it is initialized by
829 .BR "path=(.\ /bin)" .
834 are maintained together: changes to one will be reflected in the other.
835 .\" Its use is discouraged; instead use
839 .\" containing what's needed.
842 Set during initialization to
849 is run interactively, the first component of
851 is printed before reading each command.
852 The second component is printed whenever a newline is typed and more lines
853 are required to complete the command.
854 If not set in the environment, it is initialized by
855 .BR "prompt=('%\ '\ '\ ')" .
858 Set to the wait message of the last-executed program.
866 Its value is used to control execution in
875 exits at end-of-file of its input or on executing an
877 command with no argument,
884 is started with no arguments it reads commands from standard input.
885 Otherwise its first non-flag argument is the name of a file from which
886 to read commands (but see
889 Subsequent arguments become the initial value of
892 accepts the following command-line flags.
894 .TP \w'\fL-c\ \fIstring\fLXX'u
896 Commands are read from
900 Print out exit status after any command where the status is non-null.
905 is non-null after executing a simple command.
912 is given no arguments and its standard input is a terminal,
913 it runs interactively.
914 Commands are prompted for using
920 is not run interactively.
925 is given or the first character of argument zero is
929 .BR $home/lib/profile ,
930 if it exists, before reading its normal input.
939 Echo input on file descriptor 2 as it is read.
942 Print each simple command before executing it.
945 Print debugging information (internal form of commands
946 as they are executed).
952 ``Rc \- The Plan 9 Shell''.
954 There should be a way to match patterns against whole lists rather than
959 to check the value of
964 Functions that use here documents don't work.
966 Free carets don't get inserted next to keywords.
970 syntax depends on the underlying operating system
971 providing a file descriptor device tree at
974 By default, FreeBSD 5
975 does not provide file descriptors greater than 2
981 /fdescfs /dev/fd fdescfs rw 0 0
991 ensures causes FreeBSD to mount the file system
992 automatically at boot time.)
