Manual Pages  — SH

    ENV=$HOME/.shrc; export ENV

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 ( $1, $2, etc.). Otherwise, the shell reads commands from its standard input.

Unlike older versions of sh the 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 ENV scripts.

sh -T -c "trap 'exit 1' 2 ; some-blocking-program"

The -c option causes the commands to be read from the 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.

The -/+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 sh both enable the built-in emacs(1) command line editor:

set -E
set -o emacs

If used without an argument, the -o option displays the current option settings in a human-readable format. If +o is used without an argument, the current option settings are output in a format suitable for re-input into the shell.

The character ‘#’ introduces a comment if used at the beginning of a word. The word starting with ‘#’ and the rest of the line are ignored.

ASCII NUL characters (character code 0) are not allowed in shell input.

There are four types of quoting: matched single quotes, dollar-single quotes, matched double quotes, and backslash.

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).
Dollar-Single Quotes
	Enclosing characters between $' and ' preserves the literal meaning of all characters except backslashes and single quotes. A backslash introduces a C-style escape sequence:

\a	Alert (ring the terminal bell)
\b	Backspace
\cc	The control character denoted by ^c in stty(1). If c is a backslash, it must be doubled.
\e	The ESC character (ASCII 0x1b)
\f	Formfeed
\n	Newline
\r	Carriage return
\t	Horizontal tab
\v	Vertical tab
\\	Literal backslash
\amp;'	Literal single-quote
\amp;"	Literal double-quote
\nnn	The byte whose octal value is nnn (one to three digits)
\xnn	The byte whose hexadecimal value is nn (one or more digits only the last two of which are used)
\unnnn	The Unicode code point nnnn (four hexadecimal digits)
\Unnnnnnnn	The Unicode code point nnnnnnnn (eight hexadecimal digits)

The sequences for Unicode code points are currently only useful with UTF-8 locales. They reject code point 0 and UTF-16 surrogates.

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.

Any other string starting with a backslash is an error.

Double Quotes
	Enclosing characters within double quotes preserves the literal meaning of all characters except dollar sign (‘$’), backquote (‘`’), and backslash (‘\’). The backslash inside double quotes is historically weird. It remains literal unless it precedes the following characters, which it serves to quote: $ ` amp;" \ \n
Backslash	A backslash preserves the literal meaning of the following character, with the exception of the newline character (‘\n’). A backslash preceding a newline is treated as a line continuation.

1. Leading words of the form "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.
2. The remaining words are expanded as described in the section called 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 "name=value" variable assignments recognized in 1) affect the current shell.
3. Redirections are performed as described in the next section.

The 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.

[n ]> file	redirect stdout (or file descriptor n) to file
[n ]>| file
	same as above, but override the -C option
[n ]>> file
	append stdout (or file descriptor n) to file
[n ]< file	redirect stdin (or file descriptor n) from file
[n ]<> file
	redirect stdin (or file descriptor n) to and from file
[n1 ]<&n2
	duplicate stdin (or file descriptor n1) from file descriptor n2
[n ]<&-
	close stdin (or file descriptor n)
[n1 ]>&n2
	duplicate stdout (or file descriptor n1) to file descriptor n2
[n ]>&-
	close stdout (or file descriptor 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 Word Expansions). If the operator is "<<-" instead of "<<", then leading tabs in the here-doc-text are stripped.

1. Command names containing a slash are simply executed without performing any searches.
2. The shell searches each entry in the PATH variable 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 implicitly by an empty directory name, or explicitly by a single period.

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 kill -l.

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.

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.

The format for a pipeline is:

The standard output of command1 is connected to the standard input of 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.

Note that unlike some other shells, sh executes each process in a pipeline with more than one command in a subshell environment and as a child of the sh process.

If the pipeline is not in the background (discussed later), the shell waits for all commands to complete.

If the keyword !amp; does not precede the pipeline, the exit status is the exit status of the last command specified in the pipeline if the pipefail option is not set or all commands returned zero, or the last non-zero exit status of any command in the pipeline otherwise. Otherwise, the exit status is the logical NOT of that exit status. That is, if that status is zero, the exit status is 1; if that status is 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 command1 to the standard input of command2.

A ‘amp;;’ or newline terminator causes the preceding AND-OR-list (described below in the section called Short-Circuit List Operators) to be executed sequentially; an ‘&’ causes asynchronous execution of the preceding AND-OR-list.

The format for running a command in background is:

If the shell is not interactive, the standard input of an asynchronous command is set to /dev/null.

The exit status is zero.

 if list
 then list
[ elif list
 then list ]...
[ else list]
 fi

The exit status is that of selected then or else list, or zero if no list was selected.

The syntax of the while command is:

 while list
 do list
 done

The two lists are executed repeatedly while the exit status of the first list is zero. The until command is similar, but has the word until in place of while, which causes it to repeat until the exit status of the first list is zero.

The exit status is that of the last execution of the second list, or zero if it was never executed.

The syntax of the for command is:

 for variable [ in word ...]
 do list
 done

If in and the following words are omitted, inamp;"$@amp;" is used instead. The words are expanded, and then the list is executed repeatedly with the variable set to each word in turn. The do and done commands may be replaced with ‘{’ and ‘}’.

The syntax of the break and continue commands is:

The break command terminates the num innermost for or while loops. The continue command continues with the next iteration of the innermost loop. These are implemented as special built-in commands.

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 ‘amp;|’ 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 ‘;&’ instead of ‘;;’, execution continues with the next list, continuing until a list terminated with ‘;;’ or the end of the case command.

(list )

or

{ list ; }

The first form executes the commands in a subshell environment. A subshell environment has its own copy of:

1. The current working directory as set by cd.
2. The file creation mask as set by umask.
3. Resource limits as set by ulimit.
4. References to open files.
5. Traps as set by trap.
6. Known jobs.
7. Positional parameters and variables.
8. Shell options.
9. Shell functions.
10. Shell aliases.

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.

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.

For compatibility with other shells, two open parentheses in sequence should be separated by whitespace.

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:

{ echo -n "hello"; echo " world"; } > greeting

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 the local command. This should appear as the first statement of a function, and the syntax is:

The 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.

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 x is made local to function f, which then calls function g, references to the variable x made inside g will refer to the variable x declared inside f, not to the global variable named x.

The only special parameter that can be made local is ‘-’. Making ‘-’ local causes any shell options (including those that only have long names) 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

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 return command is implemented as a special built-in command.

A parameter can also be denoted by a number or a special character as explained below.

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.

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 export, local or 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 command without options.

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 @ within double-quotes, as was described above.

The order of word expansion is:

1. Tilde Expansion, Parameter Expansion, Command Substitution, 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 the -f option is in effect).
4. Quote Removal.

The ‘$’ character is used to introduce parameter expansion, command substitution, or arithmetic expansion.

where expression consists of all characters until the matching ‘}’. Any ‘}’ 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 ‘}’. If the variants with ‘+’, ‘-’, ‘=’ or ‘?amp;’ occur within a double-quoted string, as an extension there may be unquoted parts (via double-quotes inside the expansion); ‘}’ within such parts are also not examined in determining the matching ‘}’.

The simplest form for parameter expansion is:

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. Field splitting is not performed on the results of the expansion, with the exception of the special parameter @.
2. Pathname expansion is not performed on the results of the expansion.

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 parameter. In all cases, the final value of parameter is substituted. Quoting inside word does not prevent field splitting or pathname expansion. Only variables, not positional parameters 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 written 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 is unset or null; omission of the colon results in a test for a parameter that is only unset.

The 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.

${#parameter}
	String Length. The length in characters of the value of parameter.

The following four varieties of parameter expansion provide for substring processing. In each case, pattern matching notation (see Shell Patterns), rather than regular expression notation, is used to evaluate the patterns. If parameter is one of the special parameters * 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 pattern 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 pattern 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 pattern 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 pattern deleted.

or the backquoted version:

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 IFS and the quoting that is in effect. The command is executed in a subshell environment, except that the built-in commands jobid, jobs, and trap return information about the parent shell environment and times returns information about the same process if they are the only command in a command substitution.

If a command substitution of the $( form begins with a subshell, the $( and (amp; must be separated by whitespace to avoid ambiguity with arithmetic expansion.

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, arithmetic expansion and quote removal.

The allowed expressions are a subset of C expressions, summarized below.

Values	All values are of type intmax_t.
Constants
	Decimal, octal (starting with 0) and hexadecimal (starting with 0x) integer constants.
Variables
	Shell variables can be read and written and contain integer constants.
Unary operators
	! ~ + -
Binary operators
	* / % + - << >> < <= > >= == != & ^ | && || amp;
Assignment operators
	= += -= *= /= %= <<= >>= &= ^= |=
Conditional operator
	? : amp;

The result of the expression is substituted in decimal.

Characters in IFS that are whitespace ( <space>, <tab>, and <newline> ) are treated differently from other characters in IFS.

Whitespace in IFS at the beginning or end of a word is discarded.

Subsequently, a field is delimited by either

1. a non-whitespace character in IFS with any whitespace in IFS surrounding it, or
2. one or more whitespace characters in IFS.

If a word ends with a non-whitespace character in IFS, there is no empty field after this character.

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 IFS is null.

If string is not enclosed in quotes then the backslash itself must be escaped with a backslash to protect it from the shell. For example

$ echo -e "a\vb"
a
 b
$ echo -e a\\vb
a
 b
$ echo -e "a\\b"
a\b
$ echo -e a\\\\b
a\b

Only one of the -e and -n options may be specified.

eval string ...
	Concatenate all the arguments with spaces. Then re-parse and execute the command.
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 built-in command 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, if the shell is executing an 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.
export name ... export [-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 unset it. The shell allows the value of a variable to be set at the same time as it is exported by writing With no arguments the export command lists the names of all exported variables. If the -p option is specified, the exported variables are printed as " export name=value" lines, suitable for re-input to the shell.
false	A null command that returns a non-zero (false) exit value.
fc [-e editor ][first [last]] fc -l [-nr ][first [last]] fc -s [old=new ][first]
	The fc built-in command lists, or edits and re-executes, commands previously entered to an interactive shell.
-e editor
	Use the editor named by editor to edit the commands. The editor string is a command name, subject 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.
-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 determined by the value of the HISTSIZE variable. The value of first or last or both are one of the following:
[ + ]num
	A positive number representing a command number; command numbers can be displayed with the -l option.
num	A negative decimal number representing the command that was executed num of commands previously. For example, -1 is the immediately previous command.
string
	A string indicating the most recently entered command 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 embedded equal sign.

The following variables affect the execution of fc:

FCEDIT
	Name of the editor to use for history editing.
HISTSIZE
	The number of previous commands that are accessible.

fg [job]	Move the specified job or the current job to the foreground.
getopts optstring var
	The POSIX getopts command. The getopts command deprecates the older 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 OPTIND. If an option takes an argument, it is placed into the shell variable OPTARG. If an invalid option is encountered, var is set to ‘amp;?’. It returns a false value (1) when it encounters the end of the options. A new set of arguments may be parsed by assigning OPTIND=1.
hash [-rv ][command ...]
	The shell maintains a hash table which remembers the locations of commands. With no arguments whatsoever, the hash command prints out the contents of this table. With arguments, the hash command removes each specified command from the hash table (unless they are functions) and then locates it. 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 IDs of the processes in the specified job. If the job argument is omitted, use the current job.
jobs [-lps ][job ...]
	Print information about the specified jobs, or all jobs if no job argument is given. The information printed includes job ID, status and command name. If the -l option is specified, the PID of each job is also printed. If the -p option is specified, only the process IDs for the process group leaders are printed, one per line. If the -s option is specified, only the PIDs of the job commands are printed, one per line.
kill	A built-in equivalent of kill(1) that additionally supports sending signals to jobs.
local [variable ... ][-]
	See the Functions subsection.
printf	A built-in equivalent of printf(1).
pwd [-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 pwd(1) will continue to print the old name for the directory. If the -P option is specified, symbolic links are resolved. If the -L option is specified, the shell's notion of the current directory is printed (symbolic links are not resolved). This is the default.
read [-p prompt ][
	-t timeout ][-er ]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 newline is deleted from the line and the line is split as described in the section on White Space Splitting (Field Splitting)amp; 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. Backslashes are treated specially, unless the -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 IFS, even if it is. If the -t option is specified and the timeout elapses before a complete line of input is supplied, the read command will return an exit status as if terminated by SIGALRM without assigning any values. The timeout value may optionally be followed by one of ‘s’, ‘m’ or ‘h’ to explicitly specify seconds, minutes or hours. If none is supplied, ‘s’ is assumed. The -e option exists only for backward compatibility with older scripts. 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 read.
readonly [-p ][name ...]
	Each specified 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: With no arguments the readonly command lists the names of all read only variables. If the -p option is specified, the read-only variables are printed as " readonly name=value" lines, suitable for re-input to the shell.
return [exitstatus]
	See the Functions subsection.
set [-/+abCEefIimnpTuVvx ][-/+o longname ][
	-c string ][-- arg ...] The set command performs three different functions:

	With no arguments, it lists the values of all shell variables.
	If options are given, either in short form or using the long "-/+o longname" form, it sets or clears the specified options as described in the section called Argument List Processing.
	If the "--" option is specified, set will replace the shell's positional parameters with the subsequent arguments. If no arguments follow the "--" option, all the positional parameters will be cleared, which is equivalent to executing the command "shift $#". The "--" 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 (‘-’) or a plus (‘+’), which the set command will interpret as a request to enable or disable options.

setvar variable value	Assigns the specified value to the specified variable. The 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 "variable=value" rather than using setvar.
shift [n]	Shift the positional parameters n times, or once if n is not specified. 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. For portability, shifting if there are zero positional parameters should be avoided, since the shell may abort.
test	A built-in equivalent of test(1).
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.
trap [action ]signal ... trap -l
	Cause the shell to parse and execute action when any specified signal is received. The signals are specified by name or number. In addition, the pseudo-signal EXIT may be used to specify an action that is performed when the shell terminates. The action may be an empty string or a dash (‘-’); the former causes the specified signal to be ignored and the latter causes the default action to be taken. Omitting the 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 trap command has no effect on signals that were ignored on entry to the shell. Option -l causes the trap command to display a list of valid signal names.
true	A null command that returns a 0 (true) exit value.
type [name ...]	Interpret each 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.
ulimit [-HSabcdfklmnopstuvw ][limit]	Set or display resource limits (see getrlimit(2)). If limit is specified, the named resource will be set; otherwise the current resource value will be displayed. If -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 -S option specifies the soft limits instead. When displaying limits, only one of -S or -H can be given. The default is to display the soft limits, and to set both the hard and the soft limits. Option -a causes the ulimit command to display all resources. The parameter limit is not acceptable in this mode. The remaining options specify which resource value is to be displayed or modified. They are mutually exclusive.
-b sbsize
	The maximum size of socket buffer usage, in bytes.
-c coredumpsize
	The maximal size of core dump files, in 512-byte blocks. Setting coredumpsize to 0 prevents core dump files from being created.
-d datasize
	The maximal size of the data segment of a process, in kilobytes.
-f filesize
	The maximal size of a file, in 512-byte blocks.
-k kqueues
	The maximal number of kqueues (see kqueue(2)) for this user ID.
-l lockedmem
	The maximal size of memory that can be locked by a process, in kilobytes.
-m memoryuse
	The maximal resident set size of a process, in kilobytes.
-n nofiles
	The maximal number of descriptors that could be opened by a process.
-o umtxp
	The maximal number of process-shared locks (see pthread(3)) for this user ID.
-p pseudoterminals
	The maximal number of pseudo-terminals for this user ID.
-s stacksize
	The maximal size of the stack segment, in kilobytes.
-t time
	The maximal amount of CPU time to be used by each process, in seconds.
-u userproc
	The maximal number of simultaneous processes for this user ID.
-v virtualmem
	The maximal virtual size of a process, in kilobytes.
-w swapuse
	The maximum amount of swap space reserved or used for this user ID, in kilobytes.

umask [-S ][mask]
	Set the file creation mask (see umask(2)) to the octal or symbolic (see chmod(1)) value specified by mask. If the argument is omitted, the current mask value is printed. If the -S option is specified, the output is symbolic, otherwise the output is octal.
unalias [-a ][name ...]
	The specified alias names are removed. If -a is specified, all aliases are removed.
unset [-fv ]name ...
	The specified variables or functions are unset and unexported. If the -v option is specified or no options are given, the name arguments are treated as variable names. If the -f option is specified, the name arguments are treated as function names.
wait [job ...]
	Wait for each specified job to complete and return the exit status of the last process in the last specified job. If any 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.

Additionally, environment variables are turned into shell variables at startup, which may affect the shell as described under Special Variables.

This version of sh was rewritten in 1989 under the BSD license after the Bourne shell from AT&T V.4 .