+
+
+
+SH(1) BSD Reference Manual SH(1)
+
+
+N\bNA\bAM\bME\bE
+ sh - command interpreter (shell)
+
+S\bSY\bYN\bNO\bOP\bPS\bSI\bIS\bS
+ sh [-/+aCefnuvxIimsVEb] [-/+o longname] [arg ...]
+
+D\bDE\bES\bSC\bCR\bRI\bIP\bPT\bTI\bIO\bON\bN
+ Sh is the standard command interpreter for the system.
+ The current version of sh is in the process of being
+ changed to conform with the POSIX 1003.2 and 1003.2a spec-
+ ifications for the shell. This version has many features
+ which make it appear similar in some respects to the Korn
+ shell, but it is not a Korn shell clone (run GNU's bash if
+ you want that). Only features designated by POSIX, plus a
+ few Berkeley extensions, are being incorporated into this
+ shell. We expect POSIX conformance by the time 4.4 BSD is
+ released. This man page is not intended to be a tutorial
+ or a complete specification of the shell.
+
+
+ O\bOv\bve\ber\brv\bvi\bie\bew\bw
+
+
+ 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 running when a
+ user logs into the system (although a user can select a
+ different shell with the 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 and the file can be executed directly by the
+ shell.
+
+
+ I\bIn\bnv\bvo\boc\bca\bat\bti\bio\bon\bn
+
+
+ If no args are present and if the standard input of the
+ shell is connected to a terminal (or if the -i flag 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 '-', the shell is
+ also considered a login shell. This is normally done
+
+
+
+4.4BSD 1
+
+
+
+
+
+
+
+
+SH(1) BSD Reference Manual SH(1)
+
+
+ automatically by the system when the user first logs in. A
+ login shell first reads commands from the files
+ /etc/profile and .profile if they exist. If the environ-
+ ment variable ENV is set on entry to a shell, or is set in
+ the .profile of a login shell, the shell next reads com-
+ mands from the file named in ENV. Therefore, a user
+ should place commands that are to be executed only at
+ login time in the .profile file, and commands that are
+ executed for every shell inside the ENV file. To set the
+ ENV variable to some file, place the following line in
+ your .profile of your home directory
+
+ ENV=$HOME/.shinit; export ENV
+
+ substituting for ``.shinit'' any filename you wish. Since
+ the ENV file is read for every invocation of the shell,
+ including shell scripts and non-interactive shells, the
+ following paradigm is useful for restricting commands in
+ the ENV file to interactive invocations. Place commands
+ within the ``case'' and ``esac'' below (these commands are
+ described later):
+
+ case $- in *i*)
+ # commands for interactive use only
+ ...
+ esac
+
+ If command line arguments besides the options have been
+ specified, then the shell treats the first argument as the
+ name of a file from which to read commands (a shell
+ script), and the remaining arguments are set as the posi-
+ tional parameters of the shell ($1, $2, etc). Otherwise,
+ the shell reads commands from its standard input.
+
+
+ A\bAr\brg\bgu\bum\bme\ben\bnt\bt L\bLi\bis\bst\bt P\bPr\bro\boc\bce\bes\bss\bsi\bin\bng\bg
+
+
+ All of the single letter options have a corresponding name
+ that can be used as an argument to the '-o' option. The
+ set -o name is provided next to the single letter option
+ in the description below. Specifying a dash ``-'' turns
+ the option on, while using a plus ``+'' disables the
+ option. The following options can be set from the command
+ line or with the set(1) builtin (described later).
+
+ -a allexport
+ Export all variables assigned to. (UNIMPLEMENTED
+ for 4.4alpha)
+
+
+
+
+
+4.4BSD 2
+
+
+
+
+
+
+
+
+SH(1) BSD Reference Manual SH(1)
+
+
+ -C noclobber
+ Don't overwrite existing files with ``>''. (UNIM-
+ PLEMENTED for 4.4alpha)
+
+ -e errexit
+ If not interactive, exit immediately if any
+ untested command fails. The exit status of a com-
+ mand is considered to be explicitly tested if the
+ command is used to control an if, elif, while, or
+ until; or if the command is the left hand operand
+ of an ``&&'' or ``||'' operator.
+
+
+ -f noglob
+ Disable pathname expansion.
+
+ -n noexec
+ If not interactive, read commands but do not exe-
+ cute them. This is useful for checking the syntax
+ of shell scripts.
+
+ -u nounset
+ Write a message to standard error when attempting
+ to expand a variable that is not set, and if the
+ shell is not interactive, exit immediately. (UNIM-
+ PLEMENTED for 4.4alpha)
+
+ -v verbose
+ The shell writes its input to standard error as it
+ is read. Useful for debugging.
+
+ -x xtrace
+ Write each command to standard error (preceded by a
+ '+ ') before it is executed. Useful for debugging.
+
+ -I ignoreeof
+ Ignore EOF's from input when interactive.
+
+ -i interactive
+ Force the shell to behave interactively.
+
+ -m monitor
+ Turn on job control (set automatically when inter-
+ active).
+
+ -s stdin
+ Read commands from standard input (set automati-
+ cally if no file arguments are present). This
+ option has no effect when set after the shell has
+ already started running (i.e. with set(1)).
+
+
+
+
+4.4BSD 3
+
+
+
+
+
+
+
+
+SH(1) BSD Reference Manual SH(1)
+
+
+ -V vi
+ Enable the builtin vi(1) command line editor (dis-
+ ables -E if it has been set).
+
+ -E emacs
+ Enable the builtin emacs(1) command line editor
+ (disables -V if it has been set).
+
+ -b notify
+ Enable asynchronous notification of background job
+ completion. (UNIMPLEMENTED for 4.4alpha)
+
+
+
+ L\bLe\bex\bxi\bic\bca\bal\bl S\bSt\btr\bru\buc\bct\btu\bur\bre\be
+
+
+ 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 that are special to
+ the shell called ``operators''. There are two types of
+ operators: control operators and redirection operators
+ (their meaning is discussed later). Following is a list
+ of operators:
+
+ Control operators: & && ( ) ; ;; | || <newline>
+
+ Redirection operator: < > >| << >> <& >& <<- <>
+
+
+
+ Q\bQu\buo\bot\bti\bin\bng\bg
+
+
+ Quoting is used to remove the special meaning of certain
+ characters or words to the shell, such as operators,
+ whitespace, or keywords. There are three types of quot-
+ ing: matched single quotes, matched double quotes, and
+ backslash.
+
+
+ B\bBa\bac\bck\bks\bsl\bla\bas\bsh\bh
+
+
+ A backslash preserves the literal meaning of the following
+ character, with the exception of <newline>. A backslash
+ preceding a <newline> is treated as a line continuation.
+
+
+ S\bSi\bin\bng\bgl\ble\be Q\bQu\buo\bot\bte\bes\bs
+
+
+
+
+4.4BSD 4
+
+
+
+
+
+
+
+
+SH(1) BSD Reference Manual SH(1)
+
+
+ Enclosing characters in single quotes preserves the lit-
+ eral meaning of all the characters.
+
+
+ D\bDo\bou\bub\bbl\ble\be Q\bQu\buo\bot\bte\bes\bs
+
+
+ Enclosing characters within double quotes preserves the
+ literal meaning of all characters except dollarsign ($),
+ backquote (`), and backslash (\). The backslash inside
+ double quotes is historically weird, and serves to quote
+ only the following characters: $ ` " \ <newline>.
+ Otherwise it remains literal.
+
+
+ R\bRe\bes\bse\ber\brv\bve\bed\bd W\bWo\bor\brd\bds\bs
+
+
+ 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 reserved
+ words:
+
+ ! elif fi while case
+ else for then { }
+ do done until if esac
+
+ Their meaning is discussed later.
+
+
+ A\bAl\bli\bia\bas\bse\bes\bs
+
+
+ An alias is a name and corresponding value set using the
+ alias(1) builtin command. Whenever a reserved word may
+ occur (see above), and after checking for reserved words,
+ 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 ``lf''
+ with the value ``ls -F'', then the input
+
+ lf foobar <return>
+
+ would become
+
+ ls -F foobar <return>
+
+
+ Aliases provide a convenient way for naive users to create
+ shorthands for commands without having to learn how to
+ create functions with arguments. They can also be used to
+
+
+
+4.4BSD 5
+
+
+
+
+
+
+
+
+SH(1) BSD Reference Manual SH(1)
+
+
+ create lexically obscure code. This use is discouraged.
+
+
+ C\bCo\bom\bmm\bma\ban\bnd\bds\bs
+
+
+ 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 POSIX 1003.2
+ document). Essentially though, a line is read and if the
+ first word of the line (or after a control operator) is
+ not a reserved word, then the shell has recognized a sim-
+ ple command. Otherwise, a complex command or some other
+ special construct may have been recognized.
+
+
+ S\bSi\bim\bmp\bpl\ble\be C\bCo\bom\bmm\bma\ban\bnd\bds\bs
+
+
+ If a simple command has been recognized, the shell per-
+ forms the following actions:
+
+ 1) Leading words of the form ``name=value'' are stripped
+ off and assigned to the environment of the simple command.
+ Redirection operators and their arguments (as described
+ below) are stripped off and saved for processing.
+
+ 2) The remaining words are expanded as described in the
+ section called ``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
+ ``name=value'' variable assignments recognized in 1)
+ affect the current shell.
+
+ 3) Redirections are performed as described in the next
+ section.
+
+
+ R\bRe\bed\bdi\bir\bre\bec\bct\bti\bio\bon\bns\bs
+
+
+ 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:
+
+ [n] redir-op file
+
+ where redir-op is one of the redirection operators men-
+ tioned previously. Following is a list of the possible
+
+
+
+4.4BSD 6
+
+
+
+
+
+
+
+
+SH(1) BSD Reference Manual SH(1)
+
+
+ redirections. The [n] is an optional number, as in '3'
+ (not '[3]'), that refers to a file descriptor.
+
+ [n]> file
+ Redirect standard output (or n) to file.
+
+ [n]>| file
+ Same, but override the -C option.
+
+ [n]>> file
+ Append standard output (or n) to file.
+
+ [n]< file
+ Redirect standard input (or n) from file.
+
+ [n1]<&n2
+ Duplicate standard input (or n1) from file descrip-
+ tor n2.
+
+ [n]<&-
+ Close standard input (or n).
+
+ [n1]>&n2
+ Duplicate standard output (or n) from n2.
+
+ [n]>&-
+ Close standard output (or n).
+
+ [n]<> file
+ Open file for reading and writing on standard input
+ (or n).
+
+ The following redirection is often called a ``here-
+ document''.
+
+ [n]<< delimiter
+ here-doc-text...
+ delimiter
+
+ 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 n if it is specified. If the
+ delimiter as specified on the initial line is quoted, then
+ the 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
+ ``Expansions''). If the operator is ``<<-'' instead of
+ ``<<'', then leading tabs in the here-doc-text are
+ stripped.
+
+
+
+
+
+4.4BSD 7
+
+
+
+
+
+
+
+
+SH(1) BSD Reference Manual SH(1)
+
+
+ S\bSe\bea\bar\brc\bch\bh a\ban\bnd\bd E\bEx\bxe\bec\bcu\but\bti\bio\bon\bn
+
+
+ There are three types of commands: shell functions,
+ builtin commands, and normal programs -- and the command
+ is searched for (by name) in that order. They each are
+ executed in a different way.
+
+ When a shell function is executed, all of the shell posi-
+ tional parameters (except $0, which remains unchanged) are
+ set to the arguments of the shell function. The variables
+ which are explicitly placed in the environment of the com-
+ mand (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 defi-
+ nition is executed. The positional parameters are
+ restored to their original values when the command com-
+ pletes.
+
+ Shell builtins are executed internally to the shell, with-
+ out spawning a new process.
+
+ Otherwise, if the command name doesn't match a function or
+ builtin, the command is searched for as a normal program
+ in the filesystem (as described in the next section).
+ When a normal program is executed, the shell runs the pro-
+ gram, passing the arguments and the environment to the
+ program. If the program is a shell procedure, the shell
+ will interpret the program in a subshell. The shell will
+ reinitialize itself in this case, so that the effect will
+ be as if a new shell had been invoked to handle the shell
+ procedure, except that the location of commands located in
+ the parent shell will be remembered by the child.
+
+
+ P\bPa\bat\bth\bh S\bSe\bea\bar\brc\bch\bh
+
+
+ When locating a command, the shell first looks to see if
+ it has a shell function by that name. Then it looks for a
+ builtin command by that name. Finally, it searches each
+ entry in PATH in turn for the command.
+
+ The value of the PATH variable should be a series of
+ entries separated by colons. Each entry consists of a
+ directory name. The current directory may be indicated by
+ an empty directory name.
+
+ Command names containing a slash are simply executed with-
+ out performing any of the above searches.
+
+
+
+
+4.4BSD 8
+
+
+
+
+
+
+
+
+SH(1) BSD Reference Manual SH(1)
+
+
+ C\bCo\bom\bmm\bma\ban\bnd\bd E\bEx\bxi\bit\bt S\bSt\bta\bat\btu\bus\bs
+
+
+ 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 builtin com-
+ mands return exit codes, as does an executed function.
+
+
+ C\bCo\bom\bmp\bpl\ble\bex\bx C\bCo\bom\bmm\bma\ban\bnd\bds\bs
+
+
+ Complex commands are combinations of simple commands with
+ control operators or reserved words, together creating a
+ larger complex command. More generally, a command is one
+ of the following:
+
+ - simple command
+
+ - pipeline
+
+ - list or compound-list
+
+ - compound command
+
+ - function definition
+
+
+ Unless otherwise stated, the exit status of a command is
+ that of the last simple command executed by the command.
+
+
+ P\bPi\bip\bpe\bel\bli\bin\bne\be
+
+
+ A pipeline is a sequence of one or more commands separated
+ by the control operator |. The standard output of all but
+ the last command is connected to the standard input of the
+ next command.
+
+ The format for a pipeline is:
+
+ [!] command1 [ | command2 ...]
+
+
+ The standard output of command1 is connected to the stan-
+ dard input of command2. The standard input, standard out-
+ put, or both of a command is considered to be assigned by
+
+
+
+4.4BSD 9
+
+
+
+
+
+
+
+
+SH(1) BSD Reference Manual SH(1)
+
+
+ the pipeline before any redirection specified by redirec-
+ tion operators that are part of the command.
+
+ If the pipeline is not in the background (discussed
+ later), the shell waits for all commands to complete.
+
+ If the reserved word ! does not precede the pipeline, the
+ exit status is the exit status of the last command speci-
+ fied 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.
+
+ Because pipeline assignment of standard input or standard
+ output or both takes place before redirection, it can be
+ modified by redirection. For example:
+
+ $ command1 2>&1 | command2
+
+ sends both the standard output and standard error of com-
+ mand1 to the standard input of command2.
+
+ A ; or <newline> terminator causes the preceding AND-OR-
+ list (described next) to be executed sequentially; a &
+ causes asynchronous execution of the preceding AND-OR-
+ list.
+
+
+ B\bBa\bac\bck\bkg\bgr\bro\bou\bun\bnd\bd C\bCo\bom\bmm\bma\ban\bnd\bds\bs -\b--\b- &\b&
+
+
+ If a command is terminated by the control operator amper-
+ sand (&), the shell executes the command asynchronously --
+ that is, the shell does not wait for the command to finish
+ before executing the next command.
+
+ The format for running a command in background is:
+
+ command1 & [command2 & ...]
+
+ If the shell is not interactive, the standard input of an
+ asynchronous command is set to /dev/null.
+
+
+ L\bLi\bis\bst\bts\bs -\b--\b- G\bGe\ben\bne\ber\bra\bal\bll\bly\by S\bSp\bpe\bea\bak\bki\bin\bng\bg
+
+
+ A list is a sequence of zero or more commands separated by
+ newlines, semicolons, or ampersands, and optionally termi-
+ nated by one of these three characters. The commands in a
+
+
+
+4.4BSD 10
+
+
+
+
+
+
+
+
+SH(1) BSD Reference Manual SH(1)
+
+
+ list are executed in the order they are written. If com-
+ mand is followed by an ampersand, the shell starts the
+ command and immediately proceed onto the next command;
+ otherwise it waits for the command to terminate before
+ proceeding to the next one.
+
+ ``&&'' and ``||'' are AND-OR list operators. ``&&'' exe-
+ cutes the first command, and then executes the second com-
+ mand iff the exit status of the first command is zero.
+ ``||'' is similar, but executes the second command iff the
+ exit status of the first command is nonzero. ``&&'' and
+ ``||'' both have the same priority.
+
+ The syntax of the if command is
+
+ if list
+ then list
+ [ elif list
+ then list ] ...
+ [ else list ]
+ fi
+
+ The syntax of the while command is
+
+ while list
+ do list
+ done
+
+ The two lists are executed repeatedly while the exit sta-
+ tus of the first list is zero. The until command is simi-
+ lar, but has the word until in place of while repeat until
+ the exit status of the first list is zero.
+
+ The syntax of the for command is
+
+ for variable in word...
+ do list
+ done
+
+ The words are expanded, and then the list is executed
+ repeatedly with the variable set to each word in turn. do
+ and done may be replaced with ``{'' and ``}''.
+
+ The syntax of the break and continue command is
+
+ break [ num ]
+ continue [ num ]
+
+ Break terminates the num innermost for or while loops.
+ Continue continues with the next iteration of the inner-
+ most loop. These are implemented as builtin commands.
+
+
+
+4.4BSD 11
+
+
+
+
+
+
+
+
+SH(1) BSD Reference Manual SH(1)
+
+
+ The syntax of the case command is
+
+ case word in
+ pattern) list ;;
+ ...
+ esac
+
+
+ The pattern can actually be one or more patterns (see
+ Shell Patterns described later), separated by ``|'' char-
+ acters.
+
+
+ Commands may be grouped by writing either
+
+ (list)
+
+ or
+
+ { list; }
+
+ The first of these executes the commands in a subshell.
+
+
+ F\bFu\bun\bnc\bct\bti\bio\bon\bns\bs
+
+
+ The syntax of a function definition is
+
+ name ( ) command
+
+
+ A function definition is an executable statement; when
+ executed it installs a function named name and returns an
+ exit status of zero. The command is normally a list
+ enclosed between ``{'' and ``}''.
+
+ Variables may be declared to be local to a function by
+ using a local command. This should appear as the first
+ statement of a function, and the syntax is
+
+ local [ variable | - ] ...
+
+ Local is implemented as a builtin command.
+
+ 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 you make the vari-
+ able x local to function f, which then calls function g,
+
+
+
+4.4BSD 12
+
+
+
+
+
+
+
+
+SH(1) BSD Reference Manual SH(1)
+
+
+ references to the variable x made inside g will refer to
+ the variable x declared inside f, not to the global vari-
+ able named x.
+
+ The only special parameter than can be made local is
+ ``-''. Making ``-'' local any shell options that are
+ changed via the set command inside the function to be
+ restored to their original values when the function
+ returns.
+
+ The syntax of the return command is
+
+ return [ exitstatus ]
+
+ It terminates the currently executing function. Return is
+ implemented as a builtin command.
+
+
+ V\bVa\bar\bri\bia\bab\bbl\ble\bes\bs a\ban\bnd\bd P\bPa\bar\bra\bam\bme\bet\bte\ber\brs\bs
+
+
+ The shell maintains a set of parameters. A parameter
+ denoted by a name is called a variable. When starting up,
+ the shell turns all the environment variables into shell
+ variables. New variables can be set using the form
+
+ name=value
+
+
+ Variables set by the user must have a name consisting
+ solely of alphabetics, numerics, and underscores - the
+ first of which must not be numeric. A parameter can also
+ be denoted by a number or a special character as explained
+ below.
+
+
+ P\bPo\bos\bsi\bit\bti\bio\bon\bna\bal\bl P\bPa\bar\bra\bam\bme\bet\bte\ber\brs\bs
+
+
+ A positional parameter is a parameter denoted by a number
+ (n > 0). The shell sets these initially to the values of
+ its command line arguments that follow the name of the
+ shell script. The set(1) builtin can also be used to set
+ or reset them.
+
+
+ S\bSp\bpe\bec\bci\bia\bal\bl P\bPa\bar\bra\bam\bme\bet\bte\ber\brs\bs
+
+
+ A special parameter is a parameter denoted by one of the
+ following special characters. The value of the parameter
+
+
+
+4.4BSD 13
+
+
+
+
+
+
+
+
+SH(1) BSD Reference Manual SH(1)
+
+
+ is listed next to its character.
+
+ * 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 IFS variable, or by a <space> if
+ IFS is unset.
+
+ @ Expands to the positional parameters, starting from
+ one. When the expansion occurs within double-
+ quotes, each positional parameter expands as a sep-
+ arate argument. If there are no positional parame-
+ ters, the expansion of @ generates zero arguments,
+ even when @ is double-quoted. What this basically
+ means, for example, is if $1 is ``abc'' and $2 is
+ ``def ghi'', then "$@" expands to the two argu-
+ ments:
+
+ "abc" "def ghi"
+
+ # Expands to the number of positional parameters.
+
+ ? Expands to the exit status of the most recent
+ pipeline.
+
+ - (Hyphen)
+ Expands to the current option flags (the single-
+ letter option names concatenated into a string) as
+ specified on invocation, by the set builtin com-
+ mand, or implicitly by the shell.
+
+ $ Expands to the process ID of the invoked shell. A
+ subshell retains the same value of $ as its parent.
+
+ ! Expands to the process ID of the most recent back-
+ ground command executed from the current shell.
+ For a pipeline, the process ID is that of the last
+ command in the pipeline.
+
+ 0 (Zero.)
+ Expands to the name of the shell or shell script.
+
+
+
+ W\bWo\bor\brd\bd E\bEx\bxp\bpa\ban\bns\bsi\bio\bon\bns\bs
+
+
+ This clause describes the various expansions that are per-
+ formed on words. Not all expansions are performed on
+ every word, as explained later.
+
+
+
+4.4BSD 14
+
+
+
+
+
+
+
+
+SH(1) BSD Reference Manual SH(1)
+
+
+ Tilde expansions, parameter expansions, command substitu-
+ tions, 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 @ within double-quotes, as was described above.
+
+ The order of word expansion is:
+
+ (1) Tilde Expansion, Parameter Expansion, Command Substi-
+ tution, Arithmetic Expansion (these all occur at the same
+ time).
+
+ (2) Field Splitting is performed on fields generated by
+ step (1) unless the IFS variable is null.
+
+ (3) Pathname Expansion (unless set -f is in effect).
+
+ (4) Quote Removal.
+
+ The $ character is used to introduce parameter expansion,
+ command substitution, or arithmetic evaluation.
+
+
+ T\bTi\bil\bld\bde\be E\bEx\bxp\bpa\ban\bns\bsi\bio\bon\bn (\b(s\bsu\bub\bbs\bst\bti\bit\btu\but\bti\bin\bng\bg a\ba u\bus\bse\ber\br'\b's\bs h\bho\bom\bme\be d\bdi\bir\bre\bec\bct\bto\bor\bry\by)\b)
+
+
+ A word beginning with an unquoted tilde character (~) is
+ subjected to tilde expansion. All the characters up to a
+ slash (/) 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 ~/foobar), the tilde is
+ replaced with the value of the HOME variable (the current
+ user's home directory).
+
+
+
+ P\bPa\bar\bra\bam\bme\bet\bte\ber\br E\bEx\bxp\bpa\ban\bns\bsi\bio\bon\bn
+
+
+ The format for parameter expansion is as follows:
+
+ ${expression}
+
+ where expression consists of all characters until the
+ matching }. Any } escaped by a backslash or within a
+ quoted string, and characters in embedded arithmetic
+ expansions, command substitutions, and variable expan-
+ sions, are not examined in determining the matching }.
+
+
+
+
+4.4BSD 15
+
+
+
+
+
+
+
+
+SH(1) BSD Reference Manual SH(1)
+
+
+ The simplest form for parameter expansion is:
+
+ ${parameter}
+
+ The value, if any, of parameter is substituted.
+
+ 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:
+
+ 1) Pathname expansion is not performed on the results of
+ the expansion.
+
+ 2) Field splitting is not performed on the results of the
+ expansion, with the exception of @.
+
+ In addition, a parameter expansion can be modified by
+ using one of the following formats.
+
+
+ ${parameter:-word}
+ Use Default Values. If parameter is unset or null,
+ the expansion of word is substituted; otherwise,
+ the value of parameter is substituted.
+
+ ${parameter:=word}
+ Assign Default Values. If parameter is unset or
+ null, the expansion of word is assigned to parame-
+ ter. In all cases, the final value of parameter is
+ substituted. Only variables, not positional param-
+ eters or special parameters, can be assigned in
+ this way.
+
+ ${parameter:?[word]}
+ Indicate Error if Null or Unset. If parameter is
+ unset or null, the expansion of word (or a message
+ indicating it is unset if word is omitted) is writ-
+ ten to standard error and the shell exits with a
+ nonzero exit status. Otherwise, the value of
+ parameter is substituted. An interactive shell
+ need not exit.
+
+ ${parameter:+word}
+ Use Alternate Value. If parameter is unset or
+ null, null is substituted; otherwise, the expansion
+ of word is substituted.
+
+ In the parameter expansions shown previously, use of the
+ colon in the format results in a test for a parameter that
+
+
+
+4.4BSD 16
+
+
+
+
+
+
+
+
+SH(1) BSD Reference Manual SH(1)
+
+
+ is unset or null; omission of the colon results in a test
+ for a parameter that is only unset.
+
+ ${#parameter}
+ String Length. The length in characters of the
+ value of parameter.
+
+ The following four varieties of parameter expansion pro-
+ vide for substring processing. In each case, pattern
+ matching notation (see Shell Patterns), rather than regu-
+ lar expression notation, is used to evaluate the patterns.
+ If parameter is * or @, 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.
+
+ ${parameter%word}
+ Remove Smallest Suffix Pattern. The word is
+ expanded to produce a pattern. The parameter
+ expansion then results in parameter, with the
+ smallest portion of the suffix matched by the pat-
+ tern deleted.
+
+
+ ${parameter%%word}
+ Remove Largest Suffix Pattern. The word is
+ expanded to produce a pattern. The parameter
+ expansion then results in parameter, with the
+ largest portion of the suffix matched by the pat-
+ tern deleted.
+
+ ${parameter#word}
+ Remove Smallest Prefix Pattern. The word is
+ expanded to produce a pattern. The parameter
+ expansion then results in parameter, with the
+ smallest portion of the prefix matched by the pat-
+ tern deleted.
+
+ ${parameter##word}
+ Remove Largest Prefix Pattern. The word is
+ expanded to produce a pattern. The parameter
+ expansion then results in parameter, with the
+ largest portion of the prefix matched by the pat-
+ tern deleted.
+
+
+
+ C\bCo\bom\bmm\bma\ban\bnd\bd S\bSu\bub\bbs\bst\bti\bit\btu\but\bti\bio\bon\bn
+
+
+
+
+
+4.4BSD 17
+
+
+
+
+
+
+
+
+SH(1) BSD Reference Manual SH(1)
+
+
+ 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 fol-
+ lows:
+
+ $(command)
+
+ or (``backquoted'' version):
+
+ `command`
+
+
+ The shell expands the command substitution by executing
+ command in a subshell environment and replacing the com-
+ mand substitution with the standard output of the command,
+ removing sequences of one or more <newline>s at the end of
+ the substitution. (Embedded <newline>s before the end of
+ the output are not removed; however, during field split-
+ ting, they may be translated into <space>s, depending on
+ the value of IFS and quoting that is in effect.)
+
+
+
+ A\bAr\bri\bit\bth\bhm\bme\bet\bti\bic\bc E\bEx\bxp\bpa\ban\bns\bsi\bio\bon\bn
+
+
+ Arithmetic expansion provides a mechanism for evaluating
+ an arithmetic expression and substituting its value. The
+ format for arithmetic expansion is as follows:
+
+ $((expression))
+
+ The 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
+ expression for parameter expansion, command substitution,
+ and quote removal.
+
+ Next, the shell treats this as an arithmetic expression
+ and substitutes the value of the expression.
+
+
+
+ W\bWh\bhi\bit\bte\be S\bSp\bpa\bac\bce\be S\bSp\bpl\bli\bit\btt\bti\bin\bng\bg (\b(F\bFi\bie\bel\bld\bd S\bSp\bpl\bli\bit\btt\bti\bin\bng\bg)\b)
+
+
+ After parameter expansion, command substitution, and
+ arithmetic expansion the shell scans the results of expan-
+ sions and substitutions that did not occur in double-
+ quotes for field splitting and multiple fields can result.
+
+
+
+
+4.4BSD 18
+
+
+
+
+
+
+
+
+SH(1) BSD Reference Manual SH(1)
+
+
+ The shell treats each character of the IFS as a delimiter
+ and use the delimiters to split the results of parameter
+ expansion and command substitution into fields.
+
+
+
+ P\bPa\bat\bth\bhn\bna\bam\bme\be E\bEx\bxp\bpa\ban\bns\bsi\bio\bon\bn (\b(F\bFi\bil\ble\be N\bNa\bam\bme\be G\bGe\ben\bne\ber\bra\bat\bti\bio\bon\bn)\b)
+
+
+ Unless the -f flag is set, file name generation is per-
+ formed 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 pat-
+ tern. There are two restrictions on this: first, a pat-
+ tern 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 both
+ Pathname Expansion and the case(1) command.
+
+
+
+ S\bSh\bhe\bel\bll\bl P\bPa\bat\btt\bte\ber\brn\bns\bs
+
+
+ A pattern consists of normal characters, which match them-
+ selves, and meta-characters. The meta-characters are
+ ``!'', ``*'', ``?'', and ``[''. These characters lose
+ there 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.
+
+ An asterisk (``*'') matches any string of characters. A
+ question mark matches any single character. A left bracket
+ (``['') introduces a character class. The end of the
+ character class is indicated by a ``]''; if the ``]'' is
+ missing then the ``['' matches a ``['' rather than intro-
+ ducing a character class. A character class matches any
+ of the characters between the square brackets. A range
+ of characters may be specified using a minus sign. The
+ character class may be complemented by making an exclama-
+ tion point the first character of the character class.
+
+ To include a ``]'' in a character class, make it the first
+ character listed (after the ``!'', if any). To include a
+ minus sign, make it the first or last character listed
+
+
+
+
+4.4BSD 19
+
+
+
+
+
+
+
+
+SH(1) BSD Reference Manual SH(1)
+
+
+ B\bBu\bui\bil\blt\bti\bin\bns\bs
+
+
+ This section lists the builtin commands which are builtin
+ because they need to perform some operation that can't be
+ performed by a separate process. In addition to these,
+ there are several other commands that may be builtin for
+ efficiency (e.g. printf(1), echo(1), test(1), etc).
+
+ : A null command that returns a 0 (true) exit value.
+
+ . file The commands in the specified file are read and
+ executed by the shell.
+
+ alias [ name[=string] ... ]
+ If name=string is specified, the shell defines the
+ alias ``name'' with value ``string''. If just
+ ``name'' is specified, the value of the alias
+ ``name'' is printed. With no arguments, the alias
+ builtin prints the names and values of all defined
+ aliases (see unalias).
+
+ bg [ job ] ...
+ Continue the specified jobs (or the current job if
+ no jobs are given) in the background.
+
+ command command arg...
+ Execute the specified builtin command. (This is
+ useful when you have a shell function with the same
+ name as a builtin command.)
+
+ cd [ directory ]
+ Switch to the specified directory (default $HOME).
+ If the an entry for CDPATH appears in the environ-
+ ment of the cd command or the shell variable CDPATH
+ is set and the directory name does not begin with a
+ slash, then the directories listed in CDPATH will
+ be searched for the specified directory. The for-
+ mat of CDPATH is the same as that of PATH. In an
+ interactive shell, the cd command will print out
+ the name of the directory that it actually switched
+ to if this is different from the name that the user
+ gave. These may be different either because the
+ CDPATH mechanism was used or because a symbolic
+ link was crossed.
+
+ eval string...
+ Concatenate all the arguments with spaces. Then
+ re-parse and execute the command.
+
+
+
+
+
+4.4BSD 20
+
+
+
+
+
+
+
+
+SH(1) BSD Reference Manual SH(1)
+
+
+ exec [ command arg... ]
+ Unless command is omitted, the shell process is
+ replaced with the specified program (which must be
+ a real program, not a shell builtin or function).
+ Any redirections on the exec command are marked as
+ permanent, so that they are not undone when the
+ exec command finishes.
+
+ exit [ exitstatus ]
+ Terminate the shell process. If exitstatus is
+ given it is used as the exit status of the shell;
+ otherwise the exit status of the preceding command
+ is used.
+
+ export name...
+ 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 unset
+ it. The shell allows the value of a variable to be
+ set at the same time it is exported by writing
+
+ export name=value
+
+ With no arguments the export command lists the
+ names of all exported variables.
+
+ fc [-e editor] [first [last]]
+
+ fc -l [-nr] [first [last]]
+
+ fc -s [old=new] [first]
+ The fc builtin lists, or edits and re-executes,
+ commands previously entered to an interactive
+ shell.
+
+ -e editor
+ Use the editor named by editor to edit the com-
+ mands. The editor string is a command name, sub-
+ ject to search via the PATH variable. The value in
+ the FCEDIT variable is used as a default when -e is
+ not specified. If FCEDIT is null or unset, the
+ value of the EDITOR variable is used. If EDITOR is
+ null or unset, ed(1) is used as the editor.
+
+ -l (ell)
+ List the commands rather than invoking an editor on
+ them. The commands are written in the sequence
+ indicated by the first and last operands, as
+ affected by -r, with each command preceded by the
+ command number.
+
+
+
+
+4.4BSD 21
+
+
+
+
+
+
+
+
+SH(1) BSD Reference Manual SH(1)
+
+
+ -n
+ Suppress command numbers when listing with -l.
+
+ -r
+ Reverse the order of the commands listed (with -l)
+ or edited (with neither -l nor -s).
+
+ -s
+ Re-execute the command without invoking an editor.
+
+ first
+
+ last
+ Select the commands to list or edit. The number of
+ previous commands that can be accessed are deter-
+ mined by the value of the HISTSIZE variable. The
+ value of first or last or both are one of the fol-
+ lowing:
+
+ [+]number
+ A positive number representing a command number;
+ command numbers can be displayed with the -l
+ option.
+
+ -number
+ A negative decimal number representing the command
+ that was executed number of commands previously.
+ For example, -1 is the immediately previous com-
+ mand.
+
+ string
+ A string indicating the most recently entered com-
+ mand that begins with that string. If the old=new
+ operand is not also specified with -s, the string
+ form of the first operand cannot contain an embed-
+ ded equal sign.
+
+ The following environment variables affect the
+ execution of fc:
+
+ FCEDIT
+ Name of the editor to use.
+
+ HISTSIZE
+ The number of previous commands that are access-
+ able.
+
+ fg [ job ]
+ Move the specified job or the current job to the
+ foreground.
+
+
+
+
+4.4BSD 22
+
+
+
+
+
+
+
+
+SH(1) BSD Reference Manual SH(1)
+
+
+ getopts optstring var
+ The POSIX getopts command.
+
+ hash -rv command...
+ The shell maintains a hash table which remembers
+ the locations of commands. With no arguments what-
+ soever, the hash command prints out the contents
+ of this table. Entries which have not been looked
+ at since the last cd command are marked with an
+ asterisk; it is possible for these entries to be
+ invalid.
+
+ With arguments, the hash command removes the speci-
+ fied commands from the hash table (unless they are
+ functions) and then locates them. With the -v
+ option, hash prints the locations of the commands
+ as it finds them. The -r option causes the hash
+ command to delete all the entries in the hash table
+ except for functions.
+
+ jobid [ job ]
+ Print the process id's of the processes in the job.
+ If the job argument is omitted, use the current
+ job.
+
+ jobs This command lists out all the background processes
+ which are children of the current shell process.
+
+ pwd Print the current directory. The builtin command
+ may differ from the program of the same name
+ because the builtin command remembers what the cur-
+ rent directory is rather than recomputing it each
+ time. This makes it faster. However, if the cur-
+ rent directory is renamed, the builtin version of
+ pwd will continue to print the old name for the
+ directory.
+
+ read [ -p prompt ] [ -e ] variable...
+ The prompt is printed if the -p option is specified
+ and the standard input is a terminal. Then a line
+ is read from the standard input. The trailing new-
+ line is deleted from the line and the line is split
+ as described in the section on word 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
+ 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.
+
+
+
+
+4.4BSD 23
+
+
+
+
+
+
+
+
+SH(1) BSD Reference Manual SH(1)
+
+
+ The -e option causes any backslashes in the input
+ to be treated specially. If a backslash is fol-
+ lowed 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 IFS, even if it is.
+
+ readonly name...
+ The specified names are marked as read only, so
+ that they cannot be subsequently modified or unset.
+ The shell allows the value of a variable to be set
+ at the same time it is marked read only by writing
+
+ readonly name=value
+ With no arguments the readonly command lists the
+ names of all read only variables.
+
+ set [ { -options | +options | -- } ] arg...
+ The set command performs three different functions.
+
+ With no arguments, it lists the values of all shell
+ variables.
+
+ If options are given, it sets the specified option
+ flags, or clears them as described in the section
+ called ``Argument List Processing''.
+
+ The third use of the set command is to set the val-
+ ues of the shell's positional parameters to the
+ specified args. To change the positional parame-
+ ters without changing any options, use ``--'' as
+ the first argument to set. If no args are present,
+ the set command will clear all the positional
+ parameters (equivalent to executing ``shift $#''.
+
+ setvar variable value
+ Assigns value to variable. (In general it is better
+ to write variable=value rather than using setvar.
+ Setvar is intended to be used in functions that
+ assign values to variables whose names are passed
+ as parameters.)
+
+ shift [ n ]
+ Shift the positional parameters n times. A shift
+ sets the value of $1 to the value of $2, the value
+ of $2 to the value of $3, and so on, decreasing the
+ value of $# by one. If there are zero positional
+ parameters, shifting doesn't do anything.
+
+
+
+
+
+4.4BSD 24
+
+
+
+
+
+
+
+
+SH(1) BSD Reference Manual SH(1)
+
+
+ trap [ action ] signal...
+ Cause the shell to parse and execute action when
+ any of the specified signals are received. The sig-
+ nals are specified by signal number. Action may be
+ null or omitted; the former causes the specified
+ signal to be ignored and the latter causes the
+ default action to be taken. When the shell forks
+ off a subshell, it resets trapped (but not ignored)
+ signals to the default action. The trap command has
+ no effect on signals that were ignored on entry to
+ the shell.
+
+ umask [ mask ]
+ Set the value of umask (see umask(2)) to the speci-
+ fied octal value. If the argument is omitted, the
+ umask value is printed.
+
+ unalias [-a] [name]
+ If ``name'' is specified, the shell removes that
+ alias. If ``-a'' is specified, all aliases are
+ removed.
+
+ unset name...
+ The specified variables and functions are unset and
+ unexported. If a given name corresponds to both a
+ variable and a function, both the variable and the
+ function are unset.
+
+ wait [ job ]
+ Wait for the specified job to complete and return
+ the exit status of the last process in the job. If
+ the argument is omitted, wait for all jobs to com-
+ plete and the return an exit status of zero.
+
+
+
+ C\bCo\bom\bmm\bma\ban\bnd\bd L\bLi\bin\bne\be E\bEd\bdi\bit\bti\bin\bng\bg
+
+
+ When sh is being used interactively from a terminal, the
+ current command and the command history (see fc in
+ Builtins) can be edited using vi-mode command-line edit-
+ ing. This mode uses commands, described below, similar to
+ a subset of those described in the vi man page. The com-
+ mand set -o vi enables vi-mode editing and place sh into
+ vi insert mode. With vi-mode enabled, sh can be switched
+ between insert mode and command mode. The editor is not
+ described in full here, but will be in a later document.
+ It's similar to vi: typing <ESC> will throw you into com-
+ mand VI command mode. Hitting <return> while in command
+ mode will pass the line to the shell.
+
+
+
+4.4BSD 25
+
+
+
+
+
projects / unix-history / commitdiff