+.ds OK [\|
+.ds CK \|]
+.ds LT \s-2<\s0
+.ds GT \s-2>\s0
+.ds LE \s-2<\s0
+.ds ST *
+.TH SH 1
+.SH NAME
+sh,
+for,
+case,
+if,
+while,
+.BR : ,
+.BR . ,
+break,
+continue,
+cd,
+eval,
+exec,
+exit,
+export,
+login,
+newgrp,
+read,
+readonly,
+set,
+shift,
+times,
+trap,
+umask,
+wait
+\- command language
+.SH SYNOPSIS
+.B sh
+[
+.B \-ceiknrstuvx
+] [ arg ] ...
+.SH DESCRIPTION
+.I Sh
+is a command programming language
+that executes commands read from a terminal
+or a file.
+See
+.B invocation
+for the meaning of arguments to the shell.
+.PP
+.B Commands.
+.br
+A
+.I simple-command
+is a sequence of non blank
+.I words
+separated by blanks (a blank is a
+.B tab
+or a
+.BR space ).
+The first word specifies the name of the command to
+be executed.
+Except as specified below
+the remaining words are passed as arguments
+to the invoked command.
+The command name is passed as argument 0
+(see
+.IR exec (2)).
+The
+.I value
+of a simple-command is its exit status
+if it terminates normally or 200+\fIstatus\fP if
+it terminates abnormally (see
+.IR signal (2)
+for a list of
+status values).
+.LP
+A
+.I pipeline
+is a sequence of one or more
+.I commands
+separated by
+.B \(or.
+The standard output of each command but the last
+is connected by a
+.IR pipe (2)
+to the standard input of the next command.
+Each command is run as a separate process;
+the shell waits for the last command to terminate.
+.LP
+A
+.I list
+is a sequence of one or more
+.I pipelines
+separated by
+.BR ; ,
+.BR & ,
+.B &&
+or
+.B \(or\|\(or
+and optionally terminated by
+.B ;
+or
+.BR & .
+.B ;
+and
+.B &
+have equal precedence
+which is lower than that of
+.B &&
+and
+.BR \(or\|\(or ,
+.B &&
+and
+.B \(or\|\(or
+also have equal precedence.
+A semicolon causes sequential execution; an ampersand causes
+the preceding
+.I pipeline
+to be executed without waiting for it to finish.
+The symbol
+.B &&
+.RB ( \(or\|\(or )
+causes the
+.I list
+following to be executed only if the preceding
+.I pipeline
+returns a zero (non zero) value.
+Newlines may appear in a
+.I list,
+instead of semicolons,
+to delimit commands.
+.LP
+A
+.I command
+is either a simple-command
+or one of the following.
+The value returned by a command is that of the
+last simple-command executed in the command.
+.TP
+\fBfor \fIname\fR \*(OK\fBin \fIword\fR ...\*(CK \fBdo \fIlist \fBdone\fR
+Each time a
+.B for
+command is executed
+.I name
+is set to the next word in the
+.B for
+word list
+If
+.BI in \ word
+\&...
+is omitted then
+.B
+in "$@"
+is assumed.
+Execution ends when there are no more words in the list.
+.TP
+\fBcase \fIword \fBin\fR \*(OK\fIpattern \fR\*(OK \fB\(or \fIpattern \fR\*(CK ... \fB) \fIlist \fB;;\fR\*(CK ... \fBesac\fR
+A
+.B case
+command executes the
+.I list
+associated with the first
+pattern that matches
+.I word.
+The form of the patterns is
+the same as that used for
+file name generation.
+.TP
+\fBif \fIlist \fBthen \fIlist\fR \*(OK\fBelif \fIlist \fBthen \fIlist\fR\*(CK ... \*(OK\fBelse \fIlist\fR\*(CK \fBfi\fR
+The
+.I list
+following
+.B if
+is executed and if it returns zero the
+.I list
+following
+.B then
+is executed.
+Otherwise, the
+.I list
+following
+.B elif
+is executed and if its value is zero
+the
+.I list
+following
+.B then
+is executed.
+Failing that the
+.B else
+.I list
+is executed.
+.TP
+\fBwhile \fIlist\fR \*(OK\fBdo \fIlist\fR\*(CK \fBdone\fR
+A
+.B while
+command repeatedly executes the
+.B while
+.I list
+and if its value is zero executes the
+.B do
+.I list;
+otherwise the loop terminates.
+The value returned by a
+.B while
+command is that
+of the last executed command in the
+.B do
+.I list.
+.B until
+may be used in place of
+.B while
+to negate
+the loop termination test.
+.TP
+.BI ( " list " )
+Execute
+.I list
+in a subshell.
+.TP
+.BI { " list " }
+.I list
+is simply executed.
+.LP
+The following words
+are only recognized as the first word of a command
+and when not quoted.
+.IP
+.B
+if then else elif fi case in esac for while until do done { }
+.PP
+.B Command substitution.
+.br
+The standard output from a command enclosed in
+a pair of grave accents
+.RB ( \`\|\` )
+may be used as part or all
+of a word;
+trailing newlines are removed.
+.PP
+.B Parameter substitution.
+.br
+The character
+.B $
+is used to introduce substitutable
+parameters.
+Positional parameters may be assigned values by
+.BR set .
+Variables may be set by writing
+.IP
+.IB name = value
+[
+.IB name = value
+] ...
+.TP
+$\fB\|{\fIparameter\fB\|}\fR
+A
+.I parameter
+is a sequence of letters, digits or underscores (a
+.IR name ),
+a digit,
+or any of the characters
+.B
+* @ # ? \- $ !\|.
+The value, if any, of the parameter is substituted.
+The braces are required only when
+.I parameter
+is followed by a letter, digit, or underscore
+that is not to be interpreted as part of its name.
+If
+.I parameter
+is a digit then it is a positional parameter.
+If
+.I parameter
+is
+.BR * " or" " @"
+then all the positional
+parameters, starting with
+.SM
+.BR $1 ,
+are substituted
+separated by spaces.
+.SM
+.B $0
+is set from argument zero when the shell
+is invoked.
+.TP
+$\fB\|{\fIparameter\|\-word\|\fB}\fR
+If
+.I parameter
+is set then substitute its value;
+otherwise substitute
+.I word.
+.TP
+$\fB\|{\fIparameter\|\(eq\|word\|\fB}\fR
+If
+.I parameter
+is not set then set it to
+.I word;
+the value of the parameter is then substituted.
+Positional parameters may not be assigned to
+in this way.
+.TP
+$\fB\|{\fIparameter\|?\|word\|\fB}\fR
+If
+.I parameter
+is set then substitute its value;
+otherwise, print
+.I word
+and exit from the shell.
+If
+.I word
+is omitted then a standard message is printed.
+.TP
+$\fB\|{\fIparameter\|\(plword\|\fB}\fR
+If
+.I parameter
+is set then substitute
+.I word;
+otherwise substitute nothing.
+.LP
+In the above
+.I word
+is not evaluated unless it is
+to be used as the substituted string.
+(So that, for example,
+echo ${d\-\`pwd\`}
+will only execute
+.I pwd
+if
+.I d
+is unset.)
+.LP
+The following
+.I parameters
+are automatically set by the shell.
+.RS
+.TP
+.B #
+The number of positional parameters in decimal.
+.PD 0
+.TP
+.B \-
+Options supplied to the shell on invocation or by
+.BR set .
+.TP
+.B ?
+The value returned by the last executed command
+in decimal.
+.TP
+.B $
+The process number of this shell.
+.TP
+.B !
+The process number of the last background command invoked.
+.PD
+.RE
+.LP
+The following
+.I parameters
+are used but not set by the shell.
+.RS
+.TP
+.B
+.SM HOME
+The default argument (home directory) for the
+.B cd
+command.
+.PD 0
+.TP
+.B
+.SM PATH
+The search path for commands (see
+.BR execution ).
+.TP
+.B
+.SM MAIL
+If this variable is set to the name of
+a mail file then the shell informs the user of
+the arrival of mail in the specified file.
+.SM
+.TP
+.B PS1
+Primary prompt string, by default `$ '.
+.TP
+.SM
+.B PS2
+Secondary prompt string, by default `> '.
+.TP
+.SM
+.B IFS
+Internal field separators,
+normally
+.BR space ,
+.BR tab ,
+and
+.BR newline .
+.PD
+.RE
+.PP
+.B Blank interpretation.
+.br
+After parameter and command substitution,
+any results of substitution are scanned for internal field separator
+characters (those found in
+.SM
+.BR $IFS \*S)
+and split into distinct arguments where such characters are found.
+Explicit null arguments ("" or \'\') are retained.
+Implicit null arguments
+(those resulting from
+.I parameters
+that have no values) are removed.
+.PP
+.B File name generation.
+.br
+Following substitution, each command word is scanned for
+the characters
+.BR * ,
+.B ?
+and
+.B \*(OK.
+If one of these characters appears
+then the word is regarded as a pattern.
+The word is replaced with alphabetically sorted file names that match the pattern.
+If no file name is found that matches the pattern then
+the word is left unchanged.
+The character
+.B .
+at the start of a file name
+or immediately following a
+.BR / ,
+and the character
+.BR / ,
+must be matched explicitly.
+.TP
+.B \*(ST
+Matches any string, including the null string.
+.PD 0
+.TP
+.B ?
+Matches any single character.
+.TP
+.B \*(OK...\*(CK
+Matches any one of the characters
+enclosed.
+A pair of characters separated by
+.B \-
+matches any
+character lexically between the pair.
+.PD
+.PP
+.B Quoting.
+.br
+The following characters have a special meaning to the shell
+and cause termination of a word unless quoted.
+.LP
+ \fB; & ( ) \(or \*(LT \*(GT newline space tab\fP
+.LP
+A character may be
+.I quoted
+by preceding
+it with a
+.B
+\\\|.
+.B \\\\newline
+is ignored.
+All characters enclosed between a pair of quote marks (\fB\'\|\'\fP),
+except a single quote,
+are quoted.
+Inside double quotes
+(\fB"\|"\fP)
+parameter and command substitution occurs and
+.B
+\\
+quotes the characters
+.B
+\\ \` "
+and
+.BR $ \|.
+.LP
+.B
+"$*"
+is equivalent to
+.SM
+.B
+"$1 $2 ..."
+whereas
+.br
+.B
+"$@"
+is equivalent to
+.SM
+.B
+"$1" "$2" ... .
+.PP
+.B Prompting.
+.br
+When used interactively,
+the shell prompts with the value of
+.SM
+PS1
+before reading a command.
+If at any time a newline is typed and further input is needed
+to complete a command then the secondary prompt
+.RB ( \s-2$PS2\s0 )
+is issued.
+.PP
+.B Input output.
+.br
+Before a command is executed its input and output
+may be redirected using a special notation interpreted by the shell.
+The following may appear anywhere in a simple-command
+or may precede or follow a
+.I command
+and are not passed on to the invoked command.
+Substitution occurs before
+.I word
+or
+.I digit
+is used.
+.TP
+\*(LT\fI\|word\fP
+Use file
+.I word
+as standard input (file descriptor 0).
+.PD
+.TP
+\*(GT\fI\|word\fP
+Use file
+.I word
+as standard output (file descriptor 1).
+If the file does not exist then it is created;
+otherwise it is truncated to zero length.
+.TP
+\*(GT\*(GT\fI\|word\fP
+Use file
+.I word
+as standard output.
+If the file exists then output is appended (by seeking to the end);
+otherwise the file is created.
+.TP
+\*(LT\*(LT\fI\|word\fP
+The shell input is read up to a line the same as
+.IR word ,
+or end of file.
+The resulting document becomes
+the standard input.
+If any character of
+.I word
+is quoted then no interpretation
+is placed upon the characters of the document;
+otherwise, parameter and command substitution occurs,
+.B
+\\newline
+is ignored,
+and
+.B
+\\
+is used to quote the characters
+.B
+\\ $ \`
+and the first character of
+.I word.
+.TP
+\*(LT\|&\|\fIdigit\fP
+The standard input is duplicated from file descriptor
+.I digit;
+see
+.IR dup (2).
+Similarly for the standard output using \*(GT\|.
+.TP
+\*(LT\|&\|\-
+The standard input is closed.
+Similarly for the standard output using \*(GT\|.
+.PD
+.LP
+If one of the above is preceded by a digit
+then the
+file descriptor created is that specified
+by the digit
+(instead of the default 0 or 1).
+For example,
+.LP
+ \&... 2\*(GT&1
+.LP
+creates file descriptor 2 to be a duplicate
+of file descriptor 1.
+.LP
+If a command is followed by
+.B &
+then the default standard input
+for the command
+is the empty file
+(/dev/null).
+Otherwise, the environment for the execution of a command contains the
+file descriptors of the invoking shell as modified by input
+output specifications.
+.PP
+.B Environment.
+.br
+The environment
+is a list of name-value pairs that is passed to
+an executed program in the same way as a normal argument list;
+see
+.IR exec (2)
+and
+.IR environ (5).
+The shell interacts with the environment in several ways.
+On invocation, the shell scans the environment
+and creates a
+.I parameter
+for each name found,
+giving it the corresponding value.
+Executed commands inherit the same environment.
+If the user modifies the values of these
+.I parameters
+or creates new ones,
+none of these affects the environment
+unless the
+.B export
+command is used to bind the shell's
+.I parameter
+to the environment.
+The environment seen by any executed command is thus composed
+of any unmodified name-value pairs originally inherited by the shell,
+plus any modifications or additions,
+all of which must be noted in
+.B export
+commands.
+.LP
+The environment for any
+.I simple-command
+may be augmented by prefixing it with one or more assignments to
+.I parameters.
+Thus these two lines are equivalent
+.IP
+TERM=450 cmd args
+.br
+(export TERM; TERM=450; cmd args)
+.LP
+If the
+.B \-k
+flag is set,
+.I all
+keyword arguments are placed in the environment,
+even if the occur after the command name.
+The following prints `a=b c' and `c':
+.nf
+echo a=b c
+set \-k
+echo a=b c
+.fi
+.PP
+.B Signals.
+.br
+The INTERRUPT and QUIT signals for an invoked
+command are ignored if the command is followed by
+.BR & ;
+otherwise signals have the values
+inherited by the shell from its parent.
+(But see also
+.BR trap. )
+.PP
+.B Execution.
+.br
+Each time a command is executed the above substitutions
+are carried out.
+Except for the `special commands' listed below a new
+process is created and
+an attempt is made to execute the command via an
+.IR exec (2).
+.LP
+The shell parameter
+.B
+.SM $PATH
+defines the search path for
+the directory containing the command.
+Each alternative directory name is separated by
+a colon
+.RB ( : ).
+The default path is
+.BR :/bin:/usr/bin .
+If the command name contains a / then the search path
+is not used.
+Otherwise, each directory in the path is
+searched for an executable file.
+If the file has execute permission but is not an
+.I a.out
+file,
+it is assumed to be a file containing shell commands.
+A subshell (i.e., a separate process) is spawned to read it.
+A parenthesized command is also executed in
+a subshell.
+.PP
+.B Special commands.
+.br
+The following commands are executed in the shell process
+and except where specified
+no input output redirection is permitted for such commands.
+.TP
+.B :
+No effect; the command does nothing.
+.PD 0
+.TP
+.BI . \ file
+Read and execute commands from
+.I file
+and return.
+The search path
+.B
+.SM $PATH
+is used to find the directory containing
+.IR file .
+.TP
+\fBbreak\fR \*(OK\fIn\fR\*(CK
+Exit from the enclosing
+.B for
+or
+.B while
+loop, if any.
+If
+.I n
+is specified then break
+.I n
+levels.
+.TP
+\fBcontinue\fR \*(OK\fIn\fR\*(CK
+Resume the next iteration of the enclosing
+.B for
+or
+.B while
+loop.
+If
+.I n
+is specified then resume at the
+.IR n -th
+enclosing loop.
+.TP
+\fBcd\fR \*(OK\fIarg\fR\*(CK
+Change the current directory to
+.I arg.
+The shell
+parameter
+.B
+.SM $HOME
+is the default
+.IR arg .
+.TP
+\fBeval\fR \*(OK\fIarg \fR...\*(CK
+The arguments are read as input
+to the shell
+and the resulting command(s) executed.
+.TP
+\fBexec\fR \*(OK\fIarg \fR...\*(CK
+The command specified by
+the arguments is executed in place of this shell
+without creating a new process.
+Input output arguments may appear and if no other
+arguments are given cause the shell input
+output to be modified.
+.TP
+\fBexit\fR \*(OK\fIn\fR\*(CK
+Causes a non interactive shell to exit
+with the exit status specified by
+.I n.
+If
+.I n
+is omitted then the exit status is that of the last command executed.
+(An end of file will also exit from the shell.)
+.TP
+\fBexport\fR \*(OK\fIname\fR ...\*(CK
+The given names are marked
+for automatic export to the
+.I environment
+of subsequently-executed commands.
+If no arguments are given then a list of
+exportable names is printed.
+.TP
+\fBlogin\fR \*(OK\fIarg\fR ...\*(CK
+Equivalent to `exec login arg ...'.
+.TP
+\fBnewgrp\fR \*(OK\fIarg \fR...\*(CK
+Equivalent to `exec newgrp arg ...'.
+.TP
+.BI read \ name\ ...
+One line is read from the standard input;
+successive words of the input are assigned to the
+variables
+.I name
+in order,
+with leftover words to the last variable.
+The return code is 0 unless the end-of-file is encountered.
+.TP
+\fBreadonly\fR \*(OK\fIname \fR...\*(CK
+The given names are marked readonly and
+the values of the these names may not be changed
+by subsequent assignment.
+If no arguments are given then a list
+of all readonly names is printed.
+.TP
+\fBset\fR \*(OK\fB\-eknptuvx\fR \*(OK\fIarg \fR...\*(CK\*(CK
+.RS
+.PD 0
+.TP 3m
+.B \-e
+If non interactive then exit immediately if a command fails.
+.TP
+.B \-k
+All keyword arguments are placed in the environment for a command,
+not just those that precede the command name.
+.TP
+.B \-n
+Read commands but do not execute them.
+.TP
+.B \-t
+Exit after reading and executing one command.
+.TP
+.B \-u
+Treat unset variables as an error when substituting.
+.TP
+.B \-v
+Print shell input lines as they are read.
+.TP
+.B \-x
+Print commands and their arguments as they are executed.
+.TP
+.B \-
+Turn off the
+.B \-x
+and
+.B \-v
+options.
+.PD
+.LP
+These flags can also be used upon invocation of the shell.
+The current set of flags may be found in
+.BR $\- .
+.LP
+Remaining arguments are positional
+parameters and are assigned, in order, to
+.SM
+.BR $1 ,
+.SM
+.BR $2 ,
+etc.
+If no arguments are given then the values
+of all names are printed.
+.RE
+.TP
+.B shift
+The positional parameters from
+.SM
+.BR $2 ...
+are renamed
+.SM
+.BR $1 ...
+.TP
+.B times
+Print the accumulated user and system times for
+processes run from the shell.
+.TP
+\fBtrap\fR \*(OK\fIarg\fR\*(CK \*(OK\fIn\fR\*(CK ...
+.I Arg
+is a command to be read and executed when the shell
+receives signal(s)
+.I n.
+(Note that
+.I arg
+is scanned once when
+the trap is set and once when the trap
+is taken.)
+Trap commands are executed in order of signal number.
+If
+.I arg
+is absent then all trap(s)
+.I n
+are reset
+to their original values.
+If
+.I arg
+is the null
+string then this signal is ignored by the shell and by invoked commands.
+If
+.I n
+is 0 then the command
+.I arg
+is executed
+on exit from the shell,
+otherwise upon receipt of signal
+.I n
+as numbered in
+.IR signal (2).
+.I Trap
+with no arguments prints a list
+of commands associated with each signal number.
+.TP
+\fBumask \fR[ \fInnn\fR ]
+The user file creation mask is set to
+the octal value
+.I nnn
+(see
+.IR umask (2)).
+If
+.I nnn
+is omitted, the current value of the mask is printed.
+.TP
+\fBwait\fP \*(OK\fIn\fP\*(CK
+Wait for the specified process and
+report its termination status.
+If
+.I n
+is not given then all currently active child processes are waited for.
+The return code from this command is that of
+the process waited for.
+.PD
+.LP
+.PP
+.B Invocation.
+.br
+If the first character of argument zero is
+.BR \- ,
+commands are read from
+.BR \s-2$HOME\s0/.\|profile ,
+if such a file exists.
+Commands are then read as described below.
+The following flags are interpreted by the shell
+when it is invoked.
+.PD 0
+.TP 11n
+.BI \-c \ string
+If the
+.B \-c
+flag is present then
+commands are read from
+.I string\|.
+.TP 11n
+.B \-s
+If the
+.B \-s
+flag is present or if no
+arguments remain
+then commands are read from the standard input.
+Shell output is written to
+file descriptor 2.
+.TP 11n
+.B \-i
+If the
+.B \-i
+flag is present or
+if the shell input and output are attached to a terminal (as told by
+.IR gtty )
+then this shell is
+.I interactive.
+In this case the terminate signal
+SIGTERM (see
+.IR signal (2))
+is ignored (so that `kill 0'
+does not kill an interactive shell) and the interrupt signal
+SIGINT is caught and ignored
+(so that
+.B wait
+is interruptable).
+In all cases SIGQUIT is ignored by the shell.
+.PD
+.LP
+The remaining flags and arguments are described under the
+.B set
+command.
+.SH FILES
+.RB $HOME/ . \^profile
+.br
+/tmp/sh*
+.br
+/dev/null
+.SH SEE ALSO
+test(1),
+exec(2),
+.SH DIAGNOSTICS
+Errors detected by the shell, such as syntax errors
+cause the shell
+to return a non zero exit status.
+If the shell is being used non interactively
+then execution of the shell file is abandoned.
+Otherwise, the shell returns the exit status of
+the last command executed (see also
+.BR exit ).
+.SH BUGS
+If \*(LT\*(LT is used to provide standard input to an asynchronous
+process invoked by &,
+the shell gets mixed up about naming the input document.
+A garbage file /tmp/sh* is created, and the shell complains about
+not being able to find the file by another name.
projects / unix-history / commitdiff