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diff --git a/bin/cash/sh.1 b/bin/cash/sh.1 deleted file mode 100644 index 8df7d033..00000000 --- a/bin/cash/sh.1 +++ /dev/null @@ -1,2875 +0,0 @@ -.\"- -.\" Copyright (c) 1991, 1993 -.\" The Regents of the University of California. All rights reserved. -.\" -.\" This code is derived from software contributed to Berkeley by -.\" Kenneth Almquist. -.\" -.\" Redistribution and use in source and binary forms, with or without -.\" modification, are permitted provided that the following conditions -.\" are met: -.\" 1. Redistributions of source code must retain the above copyright -.\" notice, this list of conditions and the following disclaimer. -.\" 2. Redistributions in binary form must reproduce the above copyright -.\" notice, this list of conditions and the following disclaimer in the -.\" documentation and/or other materials provided with the distribution. -.\" 3. Neither the name of the University nor the names of its contributors -.\" may be used to endorse or promote products derived from this software -.\" without specific prior written permission. -.\" -.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND -.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE -.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE -.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE -.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL -.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS -.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) -.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT -.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY -.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF -.\" SUCH DAMAGE. -.\" -.\" from: @(#)sh.1 8.6 (Berkeley) 5/4/95 -.\" $FreeBSD: releng/12.0/bin/sh/sh.1 336483 2018-07-19 13:09:29Z 0mp $ -.\" -.Dd July 19, 2018 -.Dt SH 1 -.Os -.Sh NAME -.Nm sh -.Nd command interpreter (shell) -.Sh SYNOPSIS -.Nm -.Op Fl /+abCEefhIimnPpTuVvx -.Op Fl /+o Ar longname -.Oo -.Ar script -.Op Ar arg ... -.Oc -.Nm -.Op Fl /+abCEefhIimnPpTuVvx -.Op Fl /+o Ar longname -.Fl c Ar string -.Oo -.Ar name -.Op Ar arg ... -.Oc -.Nm -.Op Fl /+abCEefhIimnPpTuVvx -.Op Fl /+o Ar longname -.Fl s -.Op Ar arg ... -.Sh DESCRIPTION -The -.Nm -utility is the standard command interpreter for the system. -The current version of -.Nm -is close to the -.St -p1003.1 -specification for the shell. -It only supports features -designated by POSIX, -plus a few Berkeley extensions. -This man page is not intended to be a tutorial nor a complete -specification of the shell. -.Ss Overview -The shell is a command that reads lines from -either a file or the terminal, interprets them, and -generally executes other commands. -It is the program that is started when a user logs into the system, -although a user can select a different shell with the -.Xr chsh 1 -command. -The shell -implements a language that has flow control constructs, -a macro facility that provides a variety of features in -addition to data storage, along with built-in history and line -editing capabilities. -It incorporates many features to -aid interactive use and has the advantage that the interpretative -language is common to both interactive and non-interactive -use (shell scripts). -That is, commands can be typed directly -to the running shell or can be put into a file, -which can be executed directly by the shell. -.Ss Invocation -.\" -.\" XXX This next sentence is incredibly confusing. -.\" -If no arguments are present and if the standard input of the shell -is connected to a terminal -(or if the -.Fl i -option is set), -the shell is considered an interactive shell. -An interactive shell -generally prompts before each command and handles programming -and command errors differently (as described below). -When first starting, the shell inspects argument 0, and -if it begins with a dash -.Pq Ql - , -the shell is also considered a login shell. -This is normally done automatically by the system -when the user first logs in. -A login shell first reads commands -from the files -.Pa /etc/profile -and then -.Pa .profile -in a user's home directory, -if they exist. -If the environment variable -.Ev ENV -is set on entry to a shell, or is set in the -.Pa .profile -of a login shell, the shell then subjects its value to parameter expansion -and arithmetic expansion and reads commands from the named file. -Therefore, a user should place commands that are to be executed only -at login time in the -.Pa .profile -file, and commands that are executed for every shell inside the -.Ev ENV -file. -The user can set the -.Ev ENV -variable to some file by placing the following line in the file -.Pa .profile -in the home directory, -substituting for -.Pa .shrc -the filename desired: -.Pp -.Dl "ENV=$HOME/.shrc; export ENV" -.Pp -The first non-option argument specified on the command line -will be treated as the -name of a file from which to read commands (a shell script), and -the remaining arguments are set as the positional parameters -of the shell -.Li ( $1 , $2 , -etc.). -Otherwise, the shell reads commands -from its standard input. -.Pp -Unlike older versions of -.Nm -the -.Ev ENV -script is only sourced on invocation of interactive shells. -This -closes a well-known, and sometimes easily exploitable security -hole related to poorly thought out -.Ev ENV -scripts. -.Ss Argument List Processing -All of the single letter options to -.Nm -have a corresponding long name, -with the exception of -.Fl c -and -.Fl /+o . -These long names are provided next to the single letter options -in the descriptions below. -The long name for an option may be specified as an argument to the -.Fl /+o -option of -.Nm . -Once the shell is running, -the long name for an option may be specified as an argument to the -.Fl /+o -option of the -.Ic set -built-in command -(described later in the section called -.Sx Built-in Commands ) . -Introducing an option with a dash -.Pq Ql - -enables the option, -while using a plus -.Pq Ql + -disables the option. -A -.Dq Li -- -or plain -.Ql - -will stop option processing and will force the remaining -words on the command line to be treated as arguments. -The -.Fl /+o -and -.Fl c -options do not have long names. -They take arguments and are described after the single letter options. -.Bl -tag -width indent -.It Fl a Li allexport -Flag variables for export when assignments are made to them. -.It Fl b Li notify -Enable asynchronous notification of background job -completion. -(UNIMPLEMENTED) -.It Fl C Li noclobber -Do not overwrite existing files with -.Ql > . -.It Fl E Li emacs -Enable the built-in -.Xr emacs 1 -command line editor (disables the -.Fl V -option if it has been set; -set automatically when interactive on terminals). -.It Fl e Li errexit -Exit immediately if any untested command fails in non-interactive mode. -The exit status of a command is considered to be -explicitly tested if the command is part of the list used to control -an -.Ic if , elif , while , -or -.Ic until ; -if the command is the left -hand operand of an -.Dq Li && -or -.Dq Li || -operator; or if the command is a pipeline preceded by the -.Ic !\& -keyword. -If a shell function is executed and its exit status is explicitly -tested, all commands of the function are considered to be tested as -well. -.Pp -It is recommended to check for failures explicitly -instead of relying on -.Fl e -because it tends to behave in unexpected ways, -particularly in larger scripts. -.It Fl f Li noglob -Disable pathname expansion. -.It Fl h Li trackall -A do-nothing option for POSIX compliance. -.It Fl I Li ignoreeof -Ignore -.Dv EOF Ap s -from input when in interactive mode. -.It Fl i Li interactive -Force the shell to behave interactively. -.It Fl m Li monitor -Turn on job control (set automatically when interactive). -A new process group is created for each pipeline (called a job). -It is possible to suspend jobs or to have them run in the foreground or -in the background. -In a non-interactive shell, -this option can be set even if no terminal is available -and is useful to place processes in separate process groups. -.It Fl n Li noexec -If not interactive, read commands but do not -execute them. -This is useful for checking the -syntax of shell scripts. -.It Fl P Li physical -Change the default for the -.Ic cd -and -.Ic pwd -commands from -.Fl L -(logical directory layout) -to -.Fl P -(physical directory layout). -.It Fl p Li privileged -Turn on privileged mode. -This mode is enabled on startup -if either the effective user or group ID is not equal to the -real user or group ID. -Turning this mode off sets the -effective user and group IDs to the real user and group IDs. -When this mode is enabled for interactive shells, the file -.Pa /etc/suid_profile -is sourced instead of -.Pa ~/.profile -after -.Pa /etc/profile -is sourced, and the contents of the -.Ev ENV -variable are ignored. -.It Fl s Li stdin -Read commands from standard input (set automatically -if no file arguments are present). -This option has -no effect when set after the shell has already started -running (i.e., when set with the -.Ic set -command). -.It Fl T Li trapsasync -When waiting for a child, execute traps immediately. -If this option is not set, -traps are executed after the child exits, -as specified in -.St -p1003.2 . -This nonstandard option is useful for putting guarding shells around -children that block signals. -The surrounding shell may kill the child -or it may just return control to the tty and leave the child alone, -like this: -.Bd -literal -offset indent -sh -T -c "trap 'exit 1' 2 ; some-blocking-program" -.Ed -.It Fl u Li nounset -Write a message to standard error when attempting -to expand a variable, a positional parameter or -the special parameter -.Va \&! -that is not set, and if the -shell is not interactive, exit immediately. -.It Fl V Li vi -Enable the built-in -.Xr vi 1 -command line editor (disables -.Fl E -if it has been set). -.It Fl v Li verbose -The shell writes its input to standard error -as it is read. -Useful for debugging. -.It Fl x Li xtrace -Write each command -(preceded by the value of the -.Va PS4 -variable subjected to parameter expansion and arithmetic expansion) -to standard error before it is executed. -Useful for debugging. -.It Li nolog -Another do-nothing option for POSIX compliance. -It only has a long name. -.El -.Pp -The -.Fl c -option causes the commands to be read from the -.Ar string -operand instead of from the standard input. -Keep in mind that this option only accepts a single string as its -argument, hence multi-word strings must be quoted. -.Pp -The -.Fl /+o -option takes as its only argument the long name of an option -to be enabled or disabled. -For example, the following two invocations of -.Nm -both enable the built-in -.Xr emacs 1 -command line editor: -.Bd -literal -offset indent -set -E -set -o emacs -.Ed -.Pp -If used without an argument, the -.Fl o -option displays the current option settings in a human-readable format. -If -.Cm +o -is used without an argument, the current option settings are output -in a format suitable for re-input into the shell. -.Ss Lexical Structure -The shell reads input in terms of lines from a file and breaks -it up into words at whitespace (blanks and tabs), and at -certain sequences of -characters called -.Dq operators , -which are special to the shell. -There are two types of operators: control operators and -redirection operators (their meaning is discussed later). -The following is a list of valid operators: -.Bl -tag -width indent -.It Control operators: -.Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact -.It Li & Ta Li && Ta Li \&( Ta Li \&) Ta Li \en -.It Li ;; Ta Li ;& Ta Li \&; Ta Li \&| Ta Li || -.El -.It Redirection operators: -.Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact -.It Li < Ta Li > Ta Li << Ta Li >> Ta Li <> -.It Li <& Ta Li >& Ta Li <<- Ta Li >| Ta \& -.El -.El -.Pp -The character -.Ql # -introduces a comment if used at the beginning of a word. -The word starting with -.Ql # -and the rest of the line are ignored. -.Pp -ASCII -.Dv NUL -characters (character code 0) are not allowed in shell input. -.Ss Quoting -Quoting is used to remove the special meaning of certain characters -or words to the shell, such as operators, whitespace, keywords, -or alias names. -.Pp -There are four types of quoting: matched single quotes, -dollar-single quotes, -matched double quotes, and backslash. -.Bl -tag -width indent -.It Single Quotes -Enclosing characters in single quotes preserves the literal -meaning of all the characters (except single quotes, making -it impossible to put single-quotes in a single-quoted string). -.It Dollar-Single Quotes -Enclosing characters between -.Li $' -and -.Li ' -preserves the literal meaning of all characters -except backslashes and single quotes. -A backslash introduces a C-style escape sequence: -.Bl -tag -width xUnnnnnnnn -.It \ea -Alert (ring the terminal bell) -.It \eb -Backspace -.It \ec Ns Ar c -The control character denoted by -.Li ^ Ns Ar c -in -.Xr stty 1 . -If -.Ar c -is a backslash, it must be doubled. -.It \ee -The ESC character (ASCII 0x1b) -.It \ef -Formfeed -.It \en -Newline -.It \er -Carriage return -.It \et -Horizontal tab -.It \ev -Vertical tab -.It \e\e -Literal backslash -.It \e\&' -Literal single-quote -.It \e\&" -Literal double-quote -.It \e Ns Ar nnn -The byte whose octal value is -.Ar nnn -(one to three digits) -.It \ex Ns Ar nn -The byte whose hexadecimal value is -.Ar nn -(one or more digits only the last two of which are used) -.It \eu Ns Ar nnnn -The Unicode code point -.Ar nnnn -(four hexadecimal digits) -.It \eU Ns Ar nnnnnnnn -The Unicode code point -.Ar nnnnnnnn -(eight hexadecimal digits) -.El -.Pp -The sequences for Unicode code points are currently only useful with -UTF-8 locales. -They reject code point 0 and UTF-16 surrogates. -.Pp -If an escape sequence would produce a byte with value 0, -that byte and the rest of the string until the matching single-quote -are ignored. -.Pp -Any other string starting with a backslash is an error. -.It Double Quotes -Enclosing characters within double quotes preserves the literal -meaning of all characters except dollar sign -.Pq Ql $ , -backquote -.Pq Ql ` , -and backslash -.Pq Ql \e . -The backslash inside double quotes is historically weird. -It remains literal unless it precedes the following characters, -which it serves to quote: -.Pp -.Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact -.It Li $ Ta Li ` Ta Li \&" Ta Li \e Ta Li \en -.El -.It Backslash -A backslash preserves the literal meaning of the following -character, with the exception of the newline character -.Pq Ql \en . -A backslash preceding a newline is treated as a line continuation. -.El -.Ss Keywords -Keywords or reserved words are words that have special meaning to the -shell and are recognized at the beginning of a line and -after a control operator. -The following are keywords: -.Bl -column "doneXX" "elifXX" "elseXX" "untilXX" "whileX" -offset center -.It Li \&! Ta { Ta } Ta Ic case Ta Ic do -.It Ic done Ta Ic elif Ta Ic else Ta Ic esac Ta Ic fi -.It Ic for Ta Ic if Ta Ic then Ta Ic until Ta Ic while -.El -.Ss Aliases -An alias is a name and corresponding value set using the -.Ic alias -built-in command. -Wherever the command word of a simple command may occur, -and after checking for keywords if a keyword may occur, the shell -checks the word to see if it matches an alias. -If it does, it replaces it in the input stream with its value. -For example, if there is an alias called -.Dq Li lf -with the value -.Dq Li "ls -F" , -then the input -.Pp -.Dl "lf foobar" -.Pp -would become -.Pp -.Dl "ls -F foobar" -.Pp -Aliases are also recognized after an alias -whose value ends with a space or tab. -For example, if there is also an alias called -.Dq Li nohup -with the value -.Dq Li "nohup " , -then the input -.Pp -.Dl "nohup lf foobar" -.Pp -would become -.Pp -.Dl "nohup ls -F foobar" -.Pp -Aliases provide a convenient way for naive users to -create shorthands for commands without having to learn how -to create functions with arguments. -Using aliases in scripts is discouraged -because the command that defines them must be executed -before the code that uses them is parsed. -This is fragile and not portable. -.Pp -An alias name may be escaped in a command line, so that it is not -replaced by its alias value, by using quoting characters within or -adjacent to the alias name. -This is most often done by prefixing -an alias name with a backslash to execute a function, built-in, or -normal program with the same name. -See the -.Sx Quoting -subsection. -.Ss Commands -The shell interprets the words it reads according to a -language, the specification of which is outside the scope -of this man page (refer to the BNF in the -.St -p1003.2 -document). -Essentially though, a line is read and if -the first word of the line (or after a control operator) -is not a keyword, then the shell has recognized a -simple command. -Otherwise, a complex command or some -other special construct may have been recognized. -.Ss Simple Commands -If a simple command has been recognized, the shell performs -the following actions: -.Bl -enum -.It -Leading words of the form -.Dq Li name=value -are stripped off and assigned to the environment of -the simple command -(they do not affect expansions). -Redirection operators and -their arguments (as described below) are stripped -off and saved for processing. -.It -The remaining words are expanded as described in -the section called -.Sx Word Expansions , -and the first remaining word is considered the command -name and the command is located. -The remaining -words are considered the arguments of the command. -If no command name resulted, then the -.Dq Li name=value -variable assignments recognized in 1) affect the -current shell. -.It -Redirections are performed as described in -the next section. -.El -.Ss Redirections -Redirections are used to change where a command reads its input -or sends its output. -In general, redirections open, close, or -duplicate an existing reference to a file. -The overall format -used for redirection is: -.Pp -.D1 Oo Ar n Oc Ar redir-op file -.Pp -The -.Ar redir-op -is one of the redirection operators mentioned -previously. -The following gives some examples of how these -operators can be used. -Note that stdin and stdout are commonly used abbreviations -for standard input and standard output respectively. -.Bl -tag -width "1234567890XX" -offset indent -.It Oo Ar n Oc Ns Li > Ar file -redirect stdout (or file descriptor -.Ar n ) -to -.Ar file -.It Oo Ar n Oc Ns Li >| Ar file -same as above, but override the -.Fl C -option -.It Oo Ar n Oc Ns Li >> Ar file -append stdout (or file descriptor -.Ar n ) -to -.Ar file -.It Oo Ar n Oc Ns Li < Ar file -redirect stdin (or file descriptor -.Ar n ) -from -.Ar file -.It Oo Ar n Oc Ns Li <> Ar file -redirect stdin (or file descriptor -.Ar n ) -to and from -.Ar file -.It Oo Ar n1 Oc Ns Li <& Ns Ar n2 -duplicate stdin (or file descriptor -.Ar n1 ) -from file descriptor -.Ar n2 -.It Oo Ar n Oc Ns Li <&- -close stdin (or file descriptor -.Ar n ) -.It Oo Ar n1 Oc Ns Li >& Ns Ar n2 -duplicate stdout (or file descriptor -.Ar n1 ) -to file descriptor -.Ar n2 -.It Oo Ar n Oc Ns Li >&- -close stdout (or file descriptor -.Ar n ) -.El -.Pp -The following redirection is often called a -.Dq here-document . -.Bd -unfilled -offset indent -.Oo Ar n Oc Ns Li << Ar delimiter -.Ar here-doc-text -.Ar ... -.Ar delimiter -.Ed -.Pp -All the text on successive lines up to the delimiter is -saved away and made available to the command on standard -input, or file descriptor -.Ar n -if it is specified. -If the -.Ar delimiter -as specified on the initial line is quoted, then the -.Ar here-doc-text -is treated literally, otherwise the text is subjected to -parameter expansion, command substitution, and arithmetic -expansion (as described in the section on -.Sx Word Expansions ) . -If the operator is -.Dq Li <<- -instead of -.Dq Li << , -then leading tabs -in the -.Ar here-doc-text -are stripped. -.Ss Search and Execution -There are three types of commands: shell functions, -built-in commands, and normal programs. -The command is searched for (by name) in that order. -The three types of commands are all executed in a different way. -.Pp -When a shell function is executed, all of the shell positional -parameters (except -.Li $0 , -which remains unchanged) are -set to the arguments of the shell function. -The variables which are explicitly placed in the environment of -the command (by placing assignments to them before the -function name) are made local to the function and are set -to the values given. -Then the command given in the function definition is executed. -The positional parameters are restored to their original values -when the command completes. -This all occurs within the current shell. -.Pp -Shell built-in commands are executed internally to the shell, without -spawning a new process. -There are two kinds of built-in commands: regular and special. -Assignments before special builtins persist after they finish -executing and assignment errors, redirection errors and certain -operand errors cause a script to be aborted. -Special builtins cannot be overridden with a function. -Both regular and special builtins can affect the shell in ways -normal programs cannot. -.Pp -Otherwise, if the command name does not match a function -or built-in command, the command is searched for as a normal -program in the file system (as described in the next section). -When a normal program is executed, the shell runs the program, -passing the arguments and the environment to the program. -If the program is not a normal executable file -(i.e., if it does not begin with the -.Dq "magic number" -whose ASCII representation is -.Dq Li #! , -resulting in an -.Er ENOEXEC -return value from -.Xr execve 2 ) -but appears to be a text file, -the shell will run a new instance of -.Nm -to interpret it. -.Pp -Note that previous versions of this document -and the source code itself misleadingly and sporadically -refer to a shell script without a magic number -as a -.Dq "shell procedure" . -.Ss Path Search -When locating a command, the shell first looks to see if -it has a shell function by that name. -Then it looks for a -built-in command by that name. -If a built-in command is not found, -one of two things happen: -.Bl -enum -.It -Command names containing a slash are simply executed without -performing any searches. -.It -The shell searches each entry in the -.Va PATH -variable -in turn for the command. -The value of the -.Va PATH -variable should be a series of -entries separated by colons. -Each entry consists of a -directory name. -The current directory -may be indicated implicitly by an empty directory name, -or explicitly by a single period. -.El -.Ss Command Exit Status -Each command has an exit status that can influence the behavior -of other shell commands. -The paradigm is that a command exits -with zero for normal or success, and non-zero for failure, -error, or a false indication. -The man page for each command -should indicate the various exit codes and what they mean. -Additionally, the built-in commands return exit codes, as does -an executed shell function. -.Pp -If a command is terminated by a signal, its exit status is greater than 128. -The signal name can be found by passing the exit status to -.Li kill -l . -.Pp -If there is no command word, -the exit status is the exit status of the last command substitution executed, -or zero if the command does not contain any command substitutions. -.Ss Complex Commands -Complex commands are combinations of simple commands -with control operators or keywords, together creating a larger complex -command. -More generally, a command is one of the following: -.Bl -item -offset indent -.It -simple command -.It -pipeline -.It -list or compound-list -.It -compound command -.It -function definition -.El -.Pp -Unless otherwise stated, the exit status of a command is -that of the last simple command executed by the command, -or zero if no simple command was executed. -.Ss Pipelines -A pipeline is a sequence of one or more commands separated -by the control operator -.Ql \&| . -The standard output of all but -the last command is connected to the standard input -of the next command. -The standard output of the last -command is inherited from the shell, as usual. -.Pp -The format for a pipeline is: -.Pp -.D1 Oo Li \&! Oc Ar command1 Op Li \&| Ar command2 ... -.Pp -The standard output of -.Ar command1 -is connected to the standard input of -.Ar command2 . -The standard input, standard output, or -both of a command is considered to be assigned by the -pipeline before any redirection specified by redirection -operators that are part of the command. -.Pp -Note that unlike some other shells, -.Nm -executes each process in a pipeline with more than one command -in a subshell environment and as a child of the -.Nm -process. -.Pp -If the pipeline is not in the background (discussed later), -the shell waits for all commands to complete. -.Pp -If the keyword -.Ic !\& -does not precede the pipeline, the -exit status is the exit status of the last command specified -in the pipeline. -Otherwise, the exit status is the logical -NOT of the exit status of the last command. -That is, if -the last command returns zero, the exit status is 1; if -the last command returns greater than zero, the exit status -is zero. -.Pp -Because pipeline assignment of standard input or standard -output or both takes place before redirection, it can be -modified by redirection. -For example: -.Pp -.Dl "command1 2>&1 | command2" -.Pp -sends both the standard output and standard error of -.Ar command1 -to the standard input of -.Ar command2 . -.Pp -A -.Ql \&; -or newline terminator causes the preceding -AND-OR-list -(described below in the section called -.Sx Short-Circuit List Operators ) -to be executed sequentially; -an -.Ql & -causes asynchronous execution of the preceding AND-OR-list. -.Ss Background Commands (&) -If a command is terminated by the control operator ampersand -.Pq Ql & , -the shell executes the command in a subshell environment (see -.Sx Grouping Commands Together -below) and asynchronously; -the shell does not wait for the command to finish -before executing the next command. -.Pp -The format for running a command in background is: -.Pp -.D1 Ar command1 Li & Op Ar command2 Li & Ar ... -.Pp -If the shell is not interactive, the standard input of an -asynchronous command is set to -.Pa /dev/null . -.Pp -The exit status is zero. -.Ss Lists (Generally Speaking) -A list is a sequence of zero or more commands separated by -newlines, semicolons, or ampersands, -and optionally terminated by one of these three characters. -The commands in a -list are executed in the order they are written. -If command is followed by an ampersand, the shell starts the -command and immediately proceeds onto the next command; -otherwise it waits for the command to terminate before -proceeding to the next one. -.Ss Short-Circuit List Operators -.Dq Li && -and -.Dq Li || -are AND-OR list operators. -.Dq Li && -executes the first command, and then executes the second command -if the exit status of the first command is zero. -.Dq Li || -is similar, but executes the second command if the exit -status of the first command is nonzero. -.Dq Li && -and -.Dq Li || -both have the same priority. -.Ss Flow-Control Constructs (if, while, for, case) -The syntax of the -.Ic if -command is: -.Bd -unfilled -offset indent -compact -.Ic if Ar list -.Ic then Ar list -.Oo Ic elif Ar list -.Ic then Ar list Oc Ar ... -.Op Ic else Ar list -.Ic fi -.Ed -.Pp -The exit status is that of selected -.Ic then -or -.Ic else -list, -or zero if no list was selected. -.Pp -The syntax of the -.Ic while -command is: -.Bd -unfilled -offset indent -compact -.Ic while Ar list -.Ic do Ar list -.Ic done -.Ed -.Pp -The two lists are executed repeatedly while the exit status of the -first list is zero. -The -.Ic until -command is similar, but has the word -.Ic until -in place of -.Ic while , -which causes it to -repeat until the exit status of the first list is zero. -.Pp -The exit status is that of the last execution of the second list, -or zero if it was never executed. -.Pp -The syntax of the -.Ic for -command is: -.Bd -unfilled -offset indent -compact -.Ic for Ar variable Op Ic in Ar word ... -.Ic do Ar list -.Ic done -.Ed -.Pp -If -.Ic in -and the following words are omitted, -.Ic in Li \&"$@\&" -is used instead. -The words are expanded, and then the list is executed -repeatedly with the variable set to each word in turn. -The -.Ic do -and -.Ic done -commands may be replaced with -.Ql { -and -.Ql } . -.Pp -The syntax of the -.Ic break -and -.Ic continue -commands is: -.D1 Ic break Op Ar num -.D1 Ic continue Op Ar num -.Pp -The -.Ic break -command terminates the -.Ar num -innermost -.Ic for -or -.Ic while -loops. -The -.Ic continue -command continues with the next iteration of the innermost loop. -These are implemented as special built-in commands. -.Pp -The syntax of the -.Ic case -command is: -.Bd -unfilled -offset indent -compact -.Ic case Ar word Ic in -.Ar pattern ) Ar list Li ;; -.Ar ... -.Ic esac -.Ed -.Pp -The pattern can actually be one or more patterns -(see -.Sx Shell Patterns -described later), -separated by -.Ql \&| -characters. -Tilde expansion, parameter expansion, command substitution, -arithmetic expansion and quote removal are applied to the word. -Then, each pattern is expanded in turn using tilde expansion, -parameter expansion, command substitution and arithmetic expansion and -the expanded form of the word is checked against it. -If a match is found, the corresponding list is executed. -If the selected list is terminated by the control operator -.Ql ;& -instead of -.Ql ;; , -execution continues with the next list, -continuing until a list terminated with -.Ql ;; -or the end of the -.Ic case -command. -.Ss Grouping Commands Together -Commands may be grouped by writing either -.Pp -.Sm off -.Bd -literal -offset -ident -.Po Ar list Pc -.Ed -.Sm on -.Pp -or -.Bd -literal -offset -ident -.No { Ar list ; } -.Ed -.Pp -The first form executes the commands in a subshell environment. -A subshell environment has its own copy of: -.Bl -enum -.It -The current working directory as set by -.Ic cd . -.It -The file creation mask as set by -.Ic umask . -.It -Resource limits as set by -.Ic ulimit . -.It -References to open files. -.It -Traps as set by -.Ic trap . -.It -Known jobs. -.It -Positional parameters and variables. -.It -Shell options. -.It -Shell functions. -.It -Shell aliases. -.El -.Pp -These are copied from the parent shell environment, -except that trapped (but not ignored) signals are reset to the default action -and known jobs are cleared. -Any changes do not affect the parent shell environment. -.Pp -A subshell environment may be implemented as a child process or differently. -If job control is enabled in an interactive shell, -commands grouped in parentheses can be suspended and continued as a unit. -.Pp -For compatibility with other shells, -two open parentheses in sequence should be separated by whitespace. -.Pp -The second form never forks another shell, -so it is slightly more efficient. -Grouping commands together this way allows the user to -redirect their output as though they were one program: -.Bd -literal -offset indent -{ echo -n "hello"; echo " world"; } > greeting -.Ed -.Ss Functions -The syntax of a function definition is -.Pp -.D1 Ar name Li \&( \&) Ar command -.Pp -A function definition is an executable statement; when -executed it installs a function named -.Ar name -and returns an -exit status of zero. -The -.Ar command -is normally a list -enclosed between -.Ql { -and -.Ql } . -.Pp -Variables may be declared to be local to a function by -using the -.Ic local -command. -This should appear as the first statement of a function, -and the syntax is: -.Pp -.D1 Ic local Oo Ar variable ... Oc Op Fl -.Pp -The -.Ic local -command is implemented as a built-in command. -The exit status is zero -unless the command is not in a function or a variable name is invalid. -.Pp -When a variable is made local, it inherits the initial -value and exported and readonly flags from the variable -with the same name in the surrounding scope, if there is -one. -Otherwise, the variable is initially unset. -The shell -uses dynamic scoping, so that if the variable -.Va x -is made local to function -.Em f , -which then calls function -.Em g , -references to the variable -.Va x -made inside -.Em g -will refer to the variable -.Va x -declared inside -.Em f , -not to the global variable named -.Va x . -.Pp -The only special parameter that can be made local is -.Ql - . -Making -.Ql - -local causes any shell options -(including those that only have long names) -that are -changed via the -.Ic set -command inside the function to be -restored to their original values when the function -returns. -.Pp -The syntax of the -.Ic return -command is -.Pp -.D1 Ic return Op Ar exitstatus -.Pp -It terminates the current executional scope, returning from the closest -nested function or sourced script; -if no function or sourced script is being executed, -it exits the shell instance. -The -.Ic return -command is implemented as a special built-in command. -.Ss Variables and Parameters -The shell maintains a set of parameters. -A parameter -denoted by a name -(consisting solely -of alphabetics, numerics, and underscores, -and starting with an alphabetic or an underscore) -is called a variable. -When starting up, -the shell turns all environment variables with valid names into shell -variables. -New variables can be set using the form -.Pp -.D1 Ar name Ns = Ns Ar value -.Pp -A parameter can also be denoted by a number -or a special character as explained below. -.Pp -Assignments are expanded differently from other words: -tilde expansion is also performed after the equals sign and after any colon -and usernames are also terminated by colons, -and field splitting and pathname expansion are not performed. -.Pp -This special expansion applies not only to assignments that form a simple -command by themselves or precede a command word, -but also to words passed to the -.Ic export , -.Ic local -or -.Ic readonly -built-in commands that have this form. -For this, the builtin's name must be literal -(not the result of an expansion) -and may optionally be preceded by one or more literal instances of -.Ic command -without options. -.Ss Positional Parameters -A positional parameter is a parameter denoted by a number greater than zero. -The shell sets these initially to the values of its command line -arguments that follow the name of the shell script. -The -.Ic set -built-in command can also be used to set or reset them. -.Ss Special Parameters -Special parameters are parameters denoted by a single special character -or the digit zero. -They are shown in the following list, exactly as they would appear in input -typed by the user or in the source of a shell script. -.Bl -hang -.It Li $* -Expands to the positional parameters, starting from one. -When -the expansion occurs within a double-quoted string -it expands to a single field with the value of each parameter -separated by the first character of the -.Va IFS -variable, -or by a space if -.Va IFS -is unset. -.It Li $@ -Expands to the positional parameters, starting from one. -When -the expansion occurs within double-quotes, each positional -parameter expands as a separate argument. -If there are no positional parameters, the -expansion of -.Li @ -generates zero arguments, even when -.Li @ -is double-quoted. -What this basically means, for example, is -if -.Li $1 -is -.Dq Li abc -and -.Li $2 -is -.Dq Li "def ghi" , -then -.Li \&"$@\&" -expands to -the two arguments: -.Bd -literal -offset indent -"abc" "def ghi" -.Ed -.It Li $# -Expands to the number of positional parameters. -.It Li $? -Expands to the exit status of the most recent pipeline. -.It Li $- -(hyphen) Expands to the current option flags (the single-letter -option names concatenated into a string) as specified on -invocation, by the -.Ic set -built-in command, or implicitly -by the shell. -.It Li $$ -Expands to the process ID of the invoked shell. -A subshell -retains the same value of -.Va $ -as its parent. -.It Li $! -Expands to the process ID of the most recent background -command executed from the current shell. -For a -pipeline, the process ID is that of the last command in the -pipeline. -If this parameter is referenced, the shell will remember -the process ID and its exit status until the -.Ic wait -built-in command reports completion of the process. -.It Li $0 -(zero) Expands to the name of the shell script if passed on the command line, -the -.Ar name -operand if given (with -.Fl c ) -or otherwise argument 0 passed to the shell. -.El -.Ss Special Variables -The following variables are set by the shell or -have special meaning to it: -.Bl -tag -width ".Va HISTSIZE" -.It Va CDPATH -The search path used with the -.Ic cd -built-in. -.It Va EDITOR -The fallback editor used with the -.Ic fc -built-in. -If not set, the default editor is -.Xr ed 1 . -.It Va FCEDIT -The default editor used with the -.Ic fc -built-in. -.It Va HISTSIZE -The number of previous commands that are accessible. -.It Va HOME -The user's home directory, -used in tilde expansion and as a default directory for the -.Ic cd -built-in. -.It Va IFS -Input Field Separators. -This is initialized at startup to -.Aq space , -.Aq tab , -and -.Aq newline -in that order. -This value also applies if -.Va IFS -is unset, but not if it is set to the empty string. -See the -.Sx White Space Splitting -section for more details. -.It Va LINENO -The current line number in the script or function. -.It Va MAIL -The name of a mail file, that will be checked for the arrival of new -mail. -Overridden by -.Va MAILPATH . -.It Va MAILPATH -A colon -.Pq Ql \&: -separated list of file names, for the shell to check for incoming -mail. -This variable overrides the -.Va MAIL -setting. -There is a maximum of 10 mailboxes that can be monitored at once. -.It Va OPTIND -The index of the next argument to be processed by -.Ic getopts . -This is initialized to 1 at startup. -.It Va PATH -The default search path for executables. -See the -.Sx Path Search -section for details. -.It Va PPID -The parent process ID of the invoked shell. -This is set at startup -unless this variable is in the environment. -A later change of parent process ID is not reflected. -A subshell retains the same value of -.Va PPID . -.It Va PS1 -The primary prompt string, which defaults to -.Dq Li "$ " , -unless you are the superuser, in which case it defaults to -.Dq Li "# " . -.Va PS1 -may include any of the following formatting sequences, -which are replaced by the given information: -.Bl -tag -width indent -.It Li \eH -This system's fully-qualified hostname (FQDN). -.It Li \eh -This system's hostname. -.It Li \eW -The final component of the current working directory. -.It Li \ew -The entire path of the current working directory. -.It Li \e$ -Superuser status. -.Dq Li "$ " -for normal users and -.Dq Li "# " -for superusers. -.It Li \e\e -A literal backslash. -.El -.It Va PS2 -The secondary prompt string, which defaults to -.Dq Li "> " . -.Va PS2 -may include any of the formatting sequences from -.Va PS1 . -.It Va PS4 -The prefix for the trace output (if -.Fl x -is active). -The default is -.Dq Li "+ " . -.El -.Ss Word Expansions -This clause describes the various expansions that are -performed on words. -Not all expansions are performed on -every word, as explained later. -.Pp -Tilde expansions, parameter expansions, command substitutions, -arithmetic expansions, and quote removals that occur within -a single word expand to a single field. -It is only field -splitting or pathname expansion that can create multiple -fields from a single word. -The single exception to this rule is -the expansion of the special parameter -.Va @ -within double-quotes, -as was described above. -.Pp -The order of word expansion is: -.Bl -enum -.It -Tilde Expansion, Parameter Expansion, Command Substitution, -Arithmetic Expansion (these all occur at the same time). -.It -Field Splitting is performed on fields generated by step (1) -unless the -.Va IFS -variable is null. -.It -Pathname Expansion (unless the -.Fl f -option is in effect). -.It -Quote Removal. -.El -.Pp -The -.Ql $ -character is used to introduce parameter expansion, command -substitution, or arithmetic expansion. -.Ss Tilde Expansion (substituting a user's home directory) -A word beginning with an unquoted tilde character -.Pq Ql ~ -is -subjected to tilde expansion. -All the characters up to a slash -.Pq Ql / -or the end of the word are treated as a username -and are replaced with the user's home directory. -If the -username is missing (as in -.Pa ~/foobar ) , -the tilde is replaced with the value of the -.Va HOME -variable (the current user's home directory). -.Ss Parameter Expansion -The format for parameter expansion is as follows: -.Pp -.D1 Li ${ Ns Ar expression Ns Li } -.Pp -where -.Ar expression -consists of all characters until the matching -.Ql } . -Any -.Ql } -escaped by a backslash or within a single-quoted or double-quoted -string, and characters in -embedded arithmetic expansions, command substitutions, and variable -expansions, are not examined in determining the matching -.Ql } . -If the variants with -.Ql + , -.Ql - , -.Ql = -or -.Ql ?\& -occur within a double-quoted string, -as an extension there may be unquoted parts -(via double-quotes inside the expansion); -.Ql } -within such parts are also not examined in determining the matching -.Ql } . -.Pp -The simplest form for parameter expansion is: -.Pp -.D1 Li ${ Ns Ar parameter Ns Li } -.Pp -The value, if any, of -.Ar parameter -is substituted. -.Pp -The parameter name or symbol can be enclosed in braces, which are -optional except for positional parameters with more than one digit or -when parameter is followed by a character that could be interpreted as -part of the name. -If a parameter expansion occurs inside double-quotes: -.Bl -enum -.It -Field splitting is not performed on the results of the -expansion, with the exception of the special parameter -.Va @ . -.It -Pathname expansion is not performed on the results of the -expansion. -.El -.Pp -In addition, a parameter expansion can be modified by using one of the -following formats. -.Bl -tag -width indent -.It Li ${ Ns Ar parameter Ns Li :- Ns Ar word Ns Li } -Use Default Values. -If -.Ar parameter -is unset or null, the expansion of -.Ar word -is substituted; otherwise, the value of -.Ar parameter -is substituted. -.It Li ${ Ns Ar parameter Ns Li := Ns Ar word Ns Li } -Assign Default Values. -If -.Ar parameter -is unset or null, the expansion of -.Ar word -is assigned to -.Ar parameter . -In all cases, the -final value of -.Ar parameter -is substituted. -Quoting inside -.Ar word -does not prevent field splitting or pathname expansion. -Only variables, not positional -parameters or special parameters, can be -assigned in this way. -.It Li ${ Ns Ar parameter Ns Li :? Ns Oo Ar word Oc Ns Li } -Indicate Error if Null or Unset. -If -.Ar parameter -is unset or null, the expansion of -.Ar word -(or a message indicating it is unset if -.Ar word -is omitted) is written to standard -error and the shell exits with a nonzero -exit status. -Otherwise, the value of -.Ar parameter -is substituted. -An -interactive shell need not exit. -.It Li ${ Ns Ar parameter Ns Li :+ Ns Ar word Ns Li } -Use Alternate Value. -If -.Ar parameter -is unset or null, null is substituted; -otherwise, the expansion of -.Ar word -is substituted. -.El -.Pp -In the parameter expansions shown previously, use of the colon in the -format results in a test for a parameter that is unset or null; omission -of the colon results in a test for a parameter that is only unset. -.Pp -The -.Ar word -inherits the type of quoting -(unquoted, double-quoted or here-document) -from the surroundings, -with the exception that a backslash that quotes a closing brace is removed -during quote removal. -.Bl -tag -width indent -.It Li ${# Ns Ar parameter Ns Li } -String Length. -The length in characters of -the value of -.Ar parameter . -.El -.Pp -The following four varieties of parameter expansion provide for substring -processing. -In each case, pattern matching notation -(see -.Sx Shell Patterns ) , -rather than regular expression notation, -is used to evaluate the patterns. -If parameter is one of the special parameters -.Va * -or -.Va @ , -the result of the expansion is unspecified. -Enclosing the full parameter expansion string in double-quotes does not -cause the following four varieties of pattern characters to be quoted, -whereas quoting characters within the braces has this effect. -.Bl -tag -width indent -.It Li ${ Ns Ar parameter Ns Li % Ns Ar word Ns Li } -Remove Smallest Suffix Pattern. -The -.Ar word -is expanded to produce a pattern. -The -parameter expansion then results in -.Ar parameter , -with the smallest portion of the -suffix matched by the pattern deleted. -.It Li ${ Ns Ar parameter Ns Li %% Ns Ar word Ns Li } -Remove Largest Suffix Pattern. -The -.Ar word -is expanded to produce a pattern. -The -parameter expansion then results in -.Ar parameter , -with the largest portion of the -suffix matched by the pattern deleted. -.It Li ${ Ns Ar parameter Ns Li # Ns Ar word Ns Li } -Remove Smallest Prefix Pattern. -The -.Ar word -is expanded to produce a pattern. -The -parameter expansion then results in -.Ar parameter , -with the smallest portion of the -prefix matched by the pattern deleted. -.It Li ${ Ns Ar parameter Ns Li ## Ns Ar word Ns Li } -Remove Largest Prefix Pattern. -The -.Ar word -is expanded to produce a pattern. -The -parameter expansion then results in -.Ar parameter , -with the largest portion of the -prefix matched by the pattern deleted. -.El -.Ss Command Substitution -Command substitution allows the output of a command to be substituted in -place of the command name itself. -Command substitution occurs when -the command is enclosed as follows: -.Pp -.D1 Li $( Ns Ar command Ns Li )\& -.Pp -or the backquoted version: -.Pp -.D1 Li ` Ns Ar command Ns Li ` -.Pp -The shell expands the command substitution by executing command -and replacing the command substitution -with the standard output of the command, -removing sequences of one or more newlines at the end of the substitution. -Embedded newlines before the end of the output are not removed; -however, during field splitting, they may be translated into spaces -depending on the value of -.Va IFS -and the quoting that is in effect. -The command is executed in a subshell environment, -except that the built-in commands -.Ic jobid , -.Ic jobs , -and -.Ic trap -return information about the parent shell environment -and -.Ic times -returns information about the same process -if they are the only command in a command substitution. -.Pp -If a command substitution of the -.Li $( -form begins with a subshell, -the -.Li $( -and -.Li (\& -must be separated by whitespace -to avoid ambiguity with arithmetic expansion. -.Ss Arithmetic Expansion -Arithmetic expansion provides a mechanism for evaluating an arithmetic -expression and substituting its value. -The format for arithmetic expansion is as follows: -.Pp -.D1 Li $(( Ns Ar expression Ns Li )) -.Pp -The -.Ar expression -is treated as if it were in double-quotes, except -that a double-quote inside the expression is not treated specially. -The -shell expands all tokens in the -.Ar expression -for parameter expansion, -command substitution, -arithmetic expansion -and quote removal. -.Pp -The allowed expressions are a subset of C expressions, -summarized below. -.Bl -tag -width "Variables" -offset indent -.It Values -All values are of type -.Ft intmax_t . -.It Constants -Decimal, octal (starting with -.Li 0 ) -and hexadecimal (starting with -.Li 0x ) -integer constants. -.It Variables -Shell variables can be read and written -and contain integer constants. -.It Unary operators -.Li "! ~ + -" -.It Binary operators -.Li "* / % + - << >> < <= > >= == != & ^ | && ||"\& -.It Assignment operators -.Li "= += -= *= /= %= <<= >>= &= ^= |=" -.It Conditional operator -.Li "? :"\& -.El -.Pp -The result of the expression is substituted in decimal. -.Ss White Space Splitting (Field Splitting) -In certain contexts, -after parameter expansion, command substitution, and -arithmetic expansion the shell scans the results of -expansions and substitutions that did not occur in double-quotes for -field splitting and multiple fields can result. -.Pp -Characters in -.Va IFS -that are whitespace -.Po -.Aq space , -.Aq tab , -and -.Aq newline -.Pc -are treated differently from other characters in -.Va IFS . -.Pp -Whitespace in -.Va IFS -at the beginning or end of a word is discarded. -.Pp -Subsequently, a field is delimited by either -.Bl -enum -.It -a non-whitespace character in -.Va IFS -with any whitespace in -.Va IFS -surrounding it, or -.It -one or more whitespace characters in -.Va IFS . -.El -.Pp -If a word ends with a non-whitespace character in -.Va IFS , -there is no empty field after this character. -.Pp -If no field is delimited, the word is discarded. -In particular, if a word consists solely of an unquoted substitution -and the result of the substitution is null, -it is removed by field splitting even if -.Va IFS -is null. -.Ss Pathname Expansion (File Name Generation) -Unless the -.Fl f -option is set, -file name generation is performed -after word splitting is complete. -Each word is -viewed as a series of patterns, separated by slashes. -The -process of expansion replaces the word with the names of -all existing files whose names can be formed by replacing -each pattern with a string that matches the specified pattern. -There are two restrictions on this: first, a pattern cannot match -a string containing a slash, and second, -a pattern cannot match a string starting with a period -unless the first character of the pattern is a period. -The next section describes the patterns used for -Pathname Expansion, -the four varieties of parameter expansion for substring processing and the -.Ic case -command. -.Ss Shell Patterns -A pattern consists of normal characters, which match themselves, -and meta-characters. -The meta-characters are -.Ql * , -.Ql \&? , -and -.Ql \&[ . -These characters lose their special meanings if they are quoted. -When command or variable substitution is performed and the dollar sign -or back quotes are not double-quoted, the value of the -variable or the output of the command is scanned for these -characters and they are turned into meta-characters. -.Pp -An asterisk -.Pq Ql * -matches any string of characters. -A question mark -.Pq Ql \&? -matches any single character. -A left bracket -.Pq Ql \&[ -introduces a character class. -The end of the character class is indicated by a -.Ql \&] ; -if the -.Ql \&] -is missing then the -.Ql \&[ -matches a -.Ql \&[ -rather than introducing a character class. -A character class matches any of the characters between the square brackets. -A locale-dependent range of characters may be specified using a minus sign. -A named class of characters (see -.Xr wctype 3 ) -may be specified by surrounding the name with -.Ql \&[:\& -and -.Ql :\&] . -For example, -.Ql \&[\&[:alpha:\&]\&] -is a shell pattern that matches a single letter. -The character class may be complemented by making an exclamation point -.Pq Ql !\& -the first character of the character class. -A caret -.Pq Ql ^ -has the same effect but is non-standard. -.Pp -To include a -.Ql \&] -in a character class, make it the first character listed -(after the -.Ql \&! -or -.Ql ^ , -if any). -To include a -.Ql - , -make it the first or last character listed. -.Ss Built-in Commands -This section lists the built-in commands. -.Bl -tag -width indent -.It Ic \&: -A null command that returns a 0 (true) exit value. -.It Ic \&. Ar file -The commands in the specified file are read and executed by the shell. -The -.Ic return -command may be used to return to the -.Ic \&. -command's caller. -If -.Ar file -contains any -.Ql / -characters, it is used as is. -Otherwise, the shell searches the -.Va PATH -for the file. -If it is not found in the -.Va PATH , -it is sought in the current working directory. -.It Ic \&[ -A built-in equivalent of -.Xr test 1 . -.It Ic alias Oo Ar name Ns Oo = Ns Ar string Oc ... Oc -If -.Ar name Ns = Ns Ar string -is specified, the shell defines the alias -.Ar name -with value -.Ar string . -If just -.Ar name -is specified, the value of the alias -.Ar name -is printed. -With no arguments, the -.Ic alias -built-in command prints the names and values of all defined aliases -(see -.Ic unalias ) . -Alias values are written with appropriate quoting so that they are -suitable for re-input to the shell. -Also see the -.Sx Aliases -subsection. -.It Ic bg Op Ar job ... -Continue the specified jobs -(or the current job if no jobs are given) -in the background. -.It Ic bind Oo Fl aeklrsv Oc Oo Ar key Oo Ar command Oc Oc -List or alter key bindings for the line editor. -This command is documented in -.Xr editrc 5 . -.It Ic break Op Ar num -See the -.Sx Flow-Control Constructs -subsection. -.It Ic builtin Ar cmd Op Ar arg ... -Execute the specified built-in command, -.Ar cmd . -This is useful when the user wishes to override a shell function -with the same name as a built-in command. -.It Ic cd Oo Fl L | P Oc Oo Fl e Oc Op Ar directory -.It Ic cd Fl -Switch to the specified -.Ar directory , -to the directory specified in the -.Va HOME -environment variable if no -.Ar directory -is specified or -to the directory specified in the -.Va OLDPWD -environment variable if -.Ar directory -is -.Fl . -If -.Ar directory -does not begin with -.Pa / , \&. , -or -.Pa .. , -then the directories listed in the -.Va CDPATH -variable will be -searched for the specified -.Ar directory . -If -.Va CDPATH -is unset, the current directory is searched. -The format of -.Va CDPATH -is the same as that of -.Va PATH . -In an interactive shell, -the -.Ic cd -command will print out the name of the directory -that it actually switched to -if the -.Va CDPATH -mechanism was used or if -.Ar directory -was -.Fl . -.Pp -If the -.Fl P -option is specified, -.Pa .. -is handled physically and symbolic links are resolved before -.Pa .. -components are processed. -If the -.Fl L -option is specified, -.Pa .. -is handled logically. -This is the default. -.Pp -The -.Fl e -option causes -.Ic cd -to return exit status 1 if the full pathname of the new directory -cannot be determined reliably or at all. -Normally this is not considered an error, -although a warning is printed. -.Pp -If changing the directory fails, the exit status is greater than 1. -If the directory is changed, the exit status is 0, or also 1 if -.Fl e -was given. -.It Ic chdir -A synonym for the -.Ic cd -built-in command. -.It Ic command Oo Fl p Oc Op Ar utility Op Ar argument ... -.It Ic command Oo Fl p Oc Fl v Ar utility -.It Ic command Oo Fl p Oc Fl V Ar utility -The first form of invocation executes the specified -.Ar utility , -ignoring shell functions in the search. -If -.Ar utility -is a special builtin, -it is executed as if it were a regular builtin. -.Pp -If the -.Fl p -option is specified, the command search is performed using a -default value of -.Va PATH -that is guaranteed to find all of the standard utilities. -.Pp -If the -.Fl v -option is specified, -.Ar utility -is not executed but a description of its interpretation by the shell is -printed. -For ordinary commands the output is the path name; for shell built-in -commands, shell functions and keywords only the name is written. -Aliases are printed as -.Dq Ic alias Ar name Ns = Ns Ar value . -.Pp -The -.Fl V -option is identical to -.Fl v -except for the output. -It prints -.Dq Ar utility Ic is Ar description -where -.Ar description -is either -the path name to -.Ar utility , -a special shell builtin, -a shell builtin, -a shell function, -a shell keyword -or -an alias for -.Ar value . -.It Ic continue Op Ar num -See the -.Sx Flow-Control Constructs -subsection. -.It Ic echo Oo Fl e | n Oc Op Ar string ... -Print a space-separated list of the arguments to the standard output -and append a newline character. -.Bl -tag -width indent -.It Fl n -Suppress the output of the trailing newline. -.It Fl e -Process C-style backslash escape sequences. -The -.Ic echo -command understands the following character escapes: -.Bl -tag -width indent -.It \ea -Alert (ring the terminal bell) -.It \eb -Backspace -.It \ec -Suppress the trailing newline (this has the side-effect of truncating the -line if it is not the last character) -.It \ee -The ESC character (ASCII 0x1b) -.It \ef -Formfeed -.It \en -Newline -.It \er -Carriage return -.It \et -Horizontal tab -.It \ev -Vertical tab -.It \e\e -Literal backslash -.It \e0nnn -(Zero) The character whose octal value is -.Ar nnn -.El -.Pp -If -.Ar string -is not enclosed in quotes then the backslash itself must be escaped -with a backslash to protect it from the shell. -For example -.Bd -literal -offset indent -$ echo -e "a\evb" -a - b -$ echo -e a\e\evb -a - b -$ echo -e "a\e\eb" -a\eb -$ echo -e a\e\e\e\eb -a\eb -.Ed -.El -.Pp -Only one of the -.Fl e -and -.Fl n -options may be specified. -.It Ic eval Ar string ... -Concatenate all the arguments with spaces. -Then re-parse and execute the command. -.It Ic exec Op Ar command Op arg ... -Unless -.Ar command -is omitted, -the shell process is replaced with the specified program -(which must be a real program, not a shell built-in command or function). -Any redirections on the -.Ic exec -command are marked as permanent, -so that they are not undone when the -.Ic exec -command finishes. -.It Ic exit Op Ar exitstatus -Terminate the shell process. -If -.Ar exitstatus -is given -it is used as the exit status of the shell. -Otherwise, if the shell is executing an -.Cm EXIT -trap, the exit status of the last command before the trap is used; -if the shell is executing a trap for a signal, -the shell exits by resending the signal to itself. -Otherwise, the exit status of the preceding command is used. -The exit status should be an integer between 0 and 255. -.It Ic export Ar name ... -.It Ic export Op Fl p -The specified names are exported so that they will -appear in the environment of subsequent commands. -The only way to un-export a variable is to -.Ic unset -it. -The shell allows the value of a variable to be set -at the same time as it is exported by writing -.Pp -.D1 Ic export Ar name Ns = Ns Ar value -.Pp -With no arguments the -.Ic export -command lists the names -of all exported variables. -If the -.Fl p -option is specified, the exported variables are printed as -.Dq Ic export Ar name Ns = Ns Ar value -lines, suitable for re-input to the shell. -.It Ic false -A null command that returns a non-zero (false) exit value. -.It Ic fc Oo Fl e Ar editor Oc Op Ar first Op Ar last -.It Ic fc Fl l Oo Fl nr Oc Op Ar first Op Ar last -.It Ic fc Fl s Oo Ar old Ns = Ns Ar new Oc Op Ar first -The -.Ic fc -built-in command lists, or edits and re-executes, -commands previously entered to an interactive shell. -.Bl -tag -width indent -.It Fl e Ar editor -Use the editor named by -.Ar editor -to edit the commands. -The -.Ar editor -string is a command name, -subject to search via the -.Va PATH -variable. -The value in the -.Va FCEDIT -variable is used as a default when -.Fl e -is not specified. -If -.Va FCEDIT -is null or unset, the value of the -.Va EDITOR -variable is used. -If -.Va EDITOR -is null or unset, -.Xr ed 1 -is used as the editor. -.It Fl l No (ell) -List the commands rather than invoking -an editor on them. -The commands are written in the -sequence indicated by the -.Ar first -and -.Ar last -operands, as affected by -.Fl r , -with each command preceded by the command number. -.It Fl n -Suppress command numbers when listing with -.Fl l . -.It Fl r -Reverse the order of the commands listed -(with -.Fl l ) -or edited -(with neither -.Fl l -nor -.Fl s ) . -.It Fl s -Re-execute the command without invoking an editor. -.It Ar first -.It Ar last -Select the commands to list or edit. -The number of previous commands that can be accessed -are determined by the value of the -.Va HISTSIZE -variable. -The value of -.Ar first -or -.Ar last -or both are one of the following: -.Bl -tag -width indent -.It Oo Cm + Oc Ns Ar num -A positive number representing a command number; -command numbers can be displayed with the -.Fl l -option. -.It Fl Ar num -A negative decimal number representing the -command that was executed -.Ar num -of -commands previously. -For example, \-1 is the immediately previous command. -.It Ar string -A string indicating the most recently entered command -that begins with that string. -If the -.Ar old Ns = Ns Ar new -operand is not also specified with -.Fl s , -the string form of the first operand cannot contain an embedded equal sign. -.El -.El -.Pp -The following variables affect the execution of -.Ic fc : -.Bl -tag -width ".Va HISTSIZE" -.It Va FCEDIT -Name of the editor to use for history editing. -.It Va HISTSIZE -The number of previous commands that are accessible. -.El -.It Ic fg Op Ar job -Move the specified -.Ar job -or the current job to the foreground. -.It Ic getopts Ar optstring var -The POSIX -.Ic getopts -command. -The -.Ic getopts -command deprecates the older -.Xr getopt 1 -command. -The first argument should be a series of letters, each possibly -followed by a colon which indicates that the option takes an argument. -The specified variable is set to the parsed option. -The index of -the next argument is placed into the shell variable -.Va OPTIND . -If an option takes an argument, it is placed into the shell variable -.Va OPTARG . -If an invalid option is encountered, -.Ar var -is set to -.Ql \&? . -It returns a false value (1) when it encounters the end of the options. -A new set of arguments may be parsed by assigning -.Li OPTIND=1 . -.It Ic hash Oo Fl rv Oc Op Ar command ... -The shell maintains a hash table which remembers the locations of commands. -With no arguments whatsoever, the -.Ic hash -command prints out the contents of this table. -.Pp -With arguments, the -.Ic hash -command removes each specified -.Ar command -from the hash table (unless they are functions) and then locates it. -With the -.Fl v -option, -.Ic hash -prints the locations of the commands as it finds them. -The -.Fl r -option causes the -.Ic hash -command to delete all the entries in the hash table except for functions. -.It Ic jobid Op Ar job -Print the process IDs of the processes in the specified -.Ar job . -If the -.Ar job -argument is omitted, use the current job. -.It Ic jobs Oo Fl lps Oc Op Ar job ... -Print information about the specified jobs, or all jobs if no -.Ar job -argument is given. -The information printed includes job ID, status and command name. -.Pp -If the -.Fl l -option is specified, the PID of each job is also printed. -If the -.Fl p -option is specified, only the process IDs for the process group leaders -are printed, one per line. -If the -.Fl s -option is specified, only the PIDs of the job commands are printed, one per -line. -.It Ic kill -A built-in equivalent of -.Xr kill 1 -that additionally supports sending signals to jobs. -.It Ic local Oo Ar variable ... Oc Op Fl -See the -.Sx Functions -subsection. -.It Ic printf -A built-in equivalent of -.Xr printf 1 . -.It Ic pwd Op Fl L | P -Print the path of the current directory. -The built-in command may -differ from the program of the same name because the -built-in command remembers what the current directory -is rather than recomputing it each time. -This makes -it faster. -However, if the current directory is -renamed, -the built-in version of -.Xr pwd 1 -will continue to print the old name for the directory. -.Pp -If the -.Fl P -option is specified, symbolic links are resolved. -If the -.Fl L -option is specified, the shell's notion of the current directory -is printed (symbolic links are not resolved). -This is the default. -.It Ic read Oo Fl p Ar prompt Oc Oo -.Fl t Ar timeout Oc Oo Fl er Oc Ar variable ... -The -.Ar prompt -is printed if the -.Fl p -option is specified -and the standard input is a terminal. -Then a line is -read from the standard input. -The trailing newline -is deleted from the line and the line is split as -described in the section on -.Sx White Space Splitting (Field Splitting)\& -above, and -the pieces are assigned to the variables in order. -If there are more pieces than variables, the remaining -pieces (along with the characters in -.Va IFS -that separated them) -are assigned to the last variable. -If there are more variables than pieces, the remaining -variables are assigned the null string. -.Pp -Backslashes are treated specially, unless the -.Fl r -option is -specified. -If a backslash is followed by -a newline, the backslash and the newline will be -deleted. -If a backslash is followed by any other -character, the backslash will be deleted and the following -character will be treated as though it were not in -.Va IFS , -even if it is. -.Pp -If the -.Fl t -option is specified and the -.Ar timeout -elapses before a complete line of input is supplied, -the -.Ic read -command will return an exit status as if terminated by -.Dv SIGALRM -without assigning any values. -The -.Ar timeout -value may optionally be followed by one of -.Ql s , -.Ql m -or -.Ql h -to explicitly specify seconds, minutes or hours. -If none is supplied, -.Ql s -is assumed. -.Pp -The -.Fl e -option exists only for backward compatibility with older scripts. -.Pp -The exit status is 0 on success, 1 on end of file, -between 2 and 128 if an error occurs -and greater than 128 if a trapped signal interrupts -.Ic read . -.It Ic readonly Oo Fl p Oc Op Ar name ... -Each specified -.Ar name -is marked as read only, -so that it cannot be subsequently modified or unset. -The shell allows the value of a variable to be set -at the same time as it is marked read only -by using the following form: -.Pp -.D1 Ic readonly Ar name Ns = Ns Ar value -.Pp -With no arguments the -.Ic readonly -command lists the names of all read only variables. -If the -.Fl p -option is specified, the read-only variables are printed as -.Dq Ic readonly Ar name Ns = Ns Ar value -lines, suitable for re-input to the shell. -.It Ic return Op Ar exitstatus -See the -.Sx Functions -subsection. -.It Ic set Oo Fl /+abCEefIimnpTuVvx Oc Oo Fl /+o Ar longname Oc Oo -.Fl c Ar string Oc Op Fl - Ar arg ... -The -.Ic set -command performs three different functions: -.Bl -item -.It -With no arguments, it lists the values of all shell variables. -.It -If options are given, -either in short form or using the long -.Dq Fl /+o Ar longname -form, -it sets or clears the specified options as described in the section called -.Sx Argument List Processing . -.It -If the -.Dq Fl - -option is specified, -.Ic set -will replace the shell's positional parameters with the subsequent -arguments. -If no arguments follow the -.Dq Fl - -option, -all the positional parameters will be cleared, -which is equivalent to executing the command -.Dq Li "shift $#" . -The -.Dq Fl - -flag may be omitted when specifying arguments to be used -as positional replacement parameters. -This is not recommended, -because the first argument may begin with a dash -.Pq Ql - -or a plus -.Pq Ql + , -which the -.Ic set -command will interpret as a request to enable or disable options. -.El -.It Ic setvar Ar variable value -Assigns the specified -.Ar value -to the specified -.Ar variable . -The -.Ic setvar -command is intended to be used in functions that -assign values to variables whose names are passed as parameters. -In general it is better to write -.Dq Ar variable Ns = Ns Ar value -rather than using -.Ic setvar . -.It Ic shift Op Ar n -Shift the positional parameters -.Ar n -times, or once if -.Ar n -is not specified. -A shift sets the value of -.Li $1 -to the value of -.Li $2 , -the value of -.Li $2 -to the value of -.Li $3 , -and so on, -decreasing the value of -.Li $# -by one. -For portability, shifting if there are zero positional parameters -should be avoided, since the shell may abort. -.It Ic test -A built-in equivalent of -.Xr test 1 . -.It Ic times -Print the amount of time spent executing the shell process and its children. -The first output line shows the user and system times for the shell process -itself, the second one contains the user and system times for the -children. -.It Ic trap Oo Ar action Oc Ar signal ... -.It Ic trap Fl l -Cause the shell to parse and execute -.Ar action -when any specified -.Ar signal -is received. -The signals are specified by name or number. -In addition, the pseudo-signal -.Cm EXIT -may be used to specify an -.Ar action -that is performed when the shell terminates. -The -.Ar action -may be an empty string or a dash -.Pq Ql - ; -the former causes the specified signal to be ignored -and the latter causes the default action to be taken. -Omitting the -.Ar action -and using only signal numbers is another way to request the default action. -In a subshell or utility environment, -the shell resets trapped (but not ignored) signals to the default action. -The -.Ic trap -command has no effect on signals that were ignored on entry to the shell. -.Pp -Option -.Fl l -causes the -.Ic trap -command to display a list of valid signal names. -.It Ic true -A null command that returns a 0 (true) exit value. -.It Ic type Op Ar name ... -Interpret each -.Ar name -as a command and print the resolution of the command search. -Possible resolutions are: -shell keyword, alias, special shell builtin, shell builtin, command, -tracked alias -and not found. -For aliases the alias expansion is printed; -for commands and tracked aliases -the complete pathname of the command is printed. -.It Ic ulimit Oo Fl HSabcdfklmnopstuvw Oc Op Ar limit -Set or display resource limits (see -.Xr getrlimit 2 ) . -If -.Ar limit -is specified, the named resource will be set; -otherwise the current resource value will be displayed. -.Pp -If -.Fl H -is specified, the hard limits will be set or displayed. -While everybody is allowed to reduce a hard limit, -only the superuser can increase it. -The -.Fl S -option -specifies the soft limits instead. -When displaying limits, -only one of -.Fl S -or -.Fl H -can be given. -The default is to display the soft limits, -and to set both the hard and the soft limits. -.Pp -Option -.Fl a -causes the -.Ic ulimit -command to display all resources. -The parameter -.Ar limit -is not acceptable in this mode. -.Pp -The remaining options specify which resource value is to be -displayed or modified. -They are mutually exclusive. -.Bl -tag -width indent -.It Fl b Ar sbsize -The maximum size of socket buffer usage, in bytes. -.It Fl c Ar coredumpsize -The maximal size of core dump files, in 512-byte blocks. -Setting -.Ar coredumpsize -to 0 prevents core dump files from being created. -.It Fl d Ar datasize -The maximal size of the data segment of a process, in kilobytes. -.It Fl f Ar filesize -The maximal size of a file, in 512-byte blocks. -.It Fl k Ar kqueues -The maximal number of kqueues -(see -.Xr kqueue 2 ) -for this user ID. -.It Fl l Ar lockedmem -The maximal size of memory that can be locked by a process, in -kilobytes. -.It Fl m Ar memoryuse -The maximal resident set size of a process, in kilobytes. -.It Fl n Ar nofiles -The maximal number of descriptors that could be opened by a process. -.It Fl o Ar umtxp -The maximal number of process-shared locks -(see -.Xr pthread 3 ) -for this user ID. -.It Fl p Ar pseudoterminals -The maximal number of pseudo-terminals for this user ID. -.It Fl s Ar stacksize -The maximal size of the stack segment, in kilobytes. -.It Fl t Ar time -The maximal amount of CPU time to be used by each process, in seconds. -.It Fl u Ar userproc -The maximal number of simultaneous processes for this user ID. -.It Fl v Ar virtualmem -The maximal virtual size of a process, in kilobytes. -.It Fl w Ar swapuse -The maximum amount of swap space reserved or used for this user ID, -in kilobytes. -.El -.It Ic umask Oo Fl S Oc Op Ar mask -Set the file creation mask (see -.Xr umask 2 ) -to the octal or symbolic (see -.Xr chmod 1 ) -value specified by -.Ar mask . -If the argument is omitted, the current mask value is printed. -If the -.Fl S -option is specified, the output is symbolic, otherwise the output is octal. -.It Ic unalias Oo Fl a Oc Op Ar name ... -The specified alias names are removed. -If -.Fl a -is specified, all aliases are removed. -.It Ic unset Oo Fl fv Oc Ar name ... -The specified variables or functions are unset and unexported. -If the -.Fl v -option is specified or no options are given, the -.Ar name -arguments are treated as variable names. -If the -.Fl f -option is specified, the -.Ar name -arguments are treated as function names. -.It Ic wait Op Ar job ... -Wait for each specified -.Ar job -to complete and return the exit status of the last process in the -last specified -.Ar job . -If any -.Ar job -specified is unknown to the shell, it is treated as if it -were a known job that exited with exit status 127. -If no operands are given, wait for all jobs to complete -and return an exit status of zero. -.El -.Ss Command Line Editing -When -.Nm -is being used interactively from a terminal, the current command -and the command history -(see -.Ic fc -in -.Sx Built-in Commands ) -can be edited using -.Nm vi Ns -mode -command line editing. -This mode uses commands similar -to a subset of those described in the -.Xr vi 1 -man page. -The command -.Dq Li "set -o vi" -(or -.Dq Li "set -V" ) -enables -.Nm vi Ns -mode -editing and places -.Nm -into -.Nm vi -insert mode. -With -.Nm vi Ns -mode -enabled, -.Nm -can be switched between insert mode and command mode by typing -.Aq ESC . -Hitting -.Aq return -while in command mode will pass the line to the shell. -.Pp -Similarly, the -.Dq Li "set -o emacs" -(or -.Dq Li "set -E" ) -command can be used to enable a subset of -.Nm emacs Ns -style -command line editing features. -.Sh ENVIRONMENT -The following environment variables affect the execution of -.Nm : -.Bl -tag -width ".Ev LANGXXXXXX" -.It Ev ENV -Initialization file for interactive shells. -.It Ev LANG , Ev LC_* -Locale settings. -These are inherited by children of the shell, -and is used in a limited manner by the shell itself. -.It Ev OLDPWD -The previous current directory. -This is used and updated by -.Ic cd . -.It Ev PWD -An absolute pathname for the current directory, -possibly containing symbolic links. -This is used and updated by the shell. -.It Ev TERM -The default terminal setting for the shell. -This is inherited by children of the shell, and is used in the history -editing modes. -.El -.Pp -Additionally, environment variables are turned into shell variables -at startup, -which may affect the shell as described under -.Sx Special Variables . -.Sh FILES -.Bl -tag -width "/etc/suid_profileXX" -compact -.It Pa ~/.profile -User's login profile. -.It Pa /etc/profile -System login profile. -.It Pa /etc/shells -Shell database. -.It Pa /etc/suid_profile -Privileged shell profile. -.El -.Sh EXIT STATUS -Errors that are detected by the shell, such as a syntax error, will -cause the shell to exit with a non-zero exit status. -If the shell is not an interactive shell, the execution of the shell -file will be aborted. -Otherwise the shell will return the exit status of the last command -executed, or if the -.Ic exit -builtin is used with a numeric argument, it -will return the argument. -.Sh SEE ALSO -.Xr builtin 1 , -.Xr chsh 1 , -.Xr echo 1 , -.Xr ed 1 , -.Xr emacs 1 , -.Xr kill 1 , -.Xr printf 1 , -.Xr pwd 1 , -.Xr test 1 , -.Xr vi 1 , -.Xr execve 2 , -.Xr getrlimit 2 , -.Xr umask 2 , -.Xr wctype 3 , -.Xr editrc 5 , -.Xr shells 5 -.Sh HISTORY -A -.Nm -command, the Thompson shell, appeared in -.At v1 . -It was superseded in -.At v7 -by the Bourne shell, which inherited the name -.Nm . -.Pp -This version of -.Nm -was rewritten in 1989 under the -.Bx -license after the Bourne shell from -.At V.4 . -.Sh AUTHORS -This version of -.Nm -was originally written by -.An Kenneth Almquist . -.Sh BUGS -The -.Nm -utility does not recognize multibyte characters other than UTF-8. -Splitting using -.Va IFS -does not recognize multibyte characters. |