SH(1) FreeBSD General Commands Manual SH(1)
NAME
sh - command interpreter (shell)
SYNOPSIS
sh [-/+abCEefhIimnPpTuVvx] [-/+o longname] [script [arg ...]]
sh [-/+abCEefhIimnPpTuVvx] [-/+o longname] -c string [name [arg ...]]
sh [-/+abCEefhIimnPpTuVvx] [-/+o longname] -s [arg ...]
DESCRIPTION
The sh utility is the standard command interpreter for the system. The
current version of sh is close to the IEEE Std 1003.1 ("POSIX.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.
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 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.
Invocation
If no arguments are present and if the standard input of the shell is
connected to a terminal (or if the -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 (`-'), 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 /etc/profile and then .profile in a user's home
directory, if they exist. If the environment variable ENV is set on
entry to a shell, or is set in the .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 .profile file,
and commands that are executed for every shell inside the ENV file. The
user can set the ENV variable to some file by placing the following line
in the file .profile in the home directory, substituting for .shrc the
filename desired:
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.
Argument List Processing
All of the single letter options to sh have a corresponding long name,
with the exception of -c and -/+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 -/+o option of sh. Once
the shell is running, the long name for an option may be specified as an
argument to the -/+o option of the set built-in command (described later
in the section called Built-in Commands). Introducing an option with a
dash (`-') enables the option, while using a plus (`+') disables the
option. A "--" or plain `-' will stop option processing and will force
the remaining words on the command line to be treated as arguments. The
-/+o and -c options do not have long names. They take arguments and are
described after the single letter options.
-a allexport
Flag variables for export when assignments are made to them.
-b notify
Enable asynchronous notification of background job completion.
(UNIMPLEMENTED)
-C noclobber
Do not overwrite existing files with `>'.
-E emacs
Enable the built-in emacs(1) command line editor (disables the -V
option if it has been set; set automatically when interactive on
terminals).
-e 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 if, elif, while, or until; if the command is the left
hand operand of an "&&" or "||" operator; or if the command is a
pipeline preceded by the ! 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.
It is recommended to check for failures explicitly instead of
relying on -e because it tends to behave in unexpected ways,
particularly in larger scripts.
-f noglob
Disable pathname expansion.
-h trackall
A do-nothing option for POSIX compliance.
-I ignoreeof
Ignore EOF's from input when in interactive mode.
-i interactive
Force the shell to behave interactively.
-m 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.
-n noexec
If not interactive, read commands but do not execute them. This
is useful for checking the syntax of shell scripts.
-P physical
Change the default for the cd and pwd commands from -L (logical
directory layout) to -P (physical directory layout).
-p 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 /etc/suid_profile is
sourced instead of ~/.profile after /etc/profile is sourced, and
the contents of the ENV variable are ignored.
-s 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
set command).
-T 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 IEEE Std 1003.2 ("POSIX.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:
sh -T -c "trap 'exit 1' 2 ; some-blocking-program"
-u nounset
Write a message to standard error when attempting to expand a
variable, a positional parameter or the special parameter ! that
is not set, and if the shell is not interactive, exit
immediately.
-V vi Enable the built-in vi(1) command line editor (disables -E if it
has been set).
-v verbose
The shell writes its input to standard error as it is read.
Useful for debugging.
-x xtrace
Write each command (preceded by the value of the PS4 variable
subjected to parameter expansion and arithmetic expansion) to
standard error before it is executed. Useful for debugging.
nolog Another do-nothing option for POSIX compliance. It only has a
long name.
pipefail
Change the exit status of a pipeline to the last non-zero exit
status of any command in the pipeline, if any. Since an exit due
to SIGPIPE counts as a non-zero exit status, this option may
cause non-zero exit status for successful pipelines if a command
such as head(1) in the pipeline terminates with status 0 without
reading its input completely. This option only has a long name.
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.
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 "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:
Control operators:
& && ( ) \n
;; ;& ; | ||
Redirection operators:
< > << >> <>
<& >& <<- >|
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.
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.
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 $' and ' preserves the literal
meaning of all characters except backslashes and single quotes.
A backslash introduces a C-style escape sequence:
\a Alert (ring the terminal bell)
\b Backspace
\cc The control character denoted by ^c in stty(1). If c
is a backslash, it must be doubled.
\e The ESC character (ASCII 0x1b)
\f Formfeed
\n Newline
\r Carriage return
\t Horizontal tab
\v Vertical tab
\\ Literal backslash
\' Literal single-quote
\" Literal double-quote
\nnn The byte whose octal value is nnn (one to three
digits)
\xnn The byte whose hexadecimal value is nn (one or more
digits only the last two of which are used)
\unnnn The Unicode code point nnnn (four hexadecimal digits)
\Unnnnnnnn The Unicode code point nnnnnnnn (eight hexadecimal
digits)
The sequences for Unicode code points are currently only useful
with UTF-8 locales. They reject code point 0 and UTF-16
surrogates.
If an escape sequence would produce a byte with value 0, that
byte and the rest of the string until the matching single-quote
are ignored.
Any other string starting with a backslash is an error.
Double Quotes
Enclosing characters within double quotes preserves the literal
meaning of all characters except dollar sign (`$'), 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:
$ ` " \ \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.
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:
! { } case do
done elif else esac fi
for if then until while
Aliases
An alias is a name and corresponding value set using the 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
"lf" with the value "ls -F", then the input
lf foobar
would become
ls -F foobar
Aliases are also recognized after an alias whose value ends with a space
or tab. For example, if there is also an alias called "nohup" with the
value "nohup ", then the input
nohup lf foobar
would become
nohup ls -F foobar
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.
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 Quoting subsection.
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 IEEE Std 1003.2 ("POSIX.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.
Simple Commands
If a simple command has been recognized, the shell performs the following
actions:
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.
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:
[n] redir-op file
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.
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.
When a shell function is executed, all of the shell positional 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 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.
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.
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 "magic number" whose ASCII
representation is "#!", resulting in an ENOEXEC return value from
execve(2)) but appears to be a text file, the shell will run a new
instance of sh to interpret it.
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 "shell procedure".
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:
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.
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.
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.
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:
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, or zero if no simple command was
executed.
Pipelines
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 standard output
of the last command is inherited from the shell, as usual.
The format for a pipeline is:
[!] command1 [| command2 ...]
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 ! 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 `;' 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.
Background Commands (&)
If a command is terminated by the control operator ampersand (`&'), the
shell executes the command in a subshell environment (see Grouping
Commands Together below) and asynchronously; 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.
The exit status is zero.
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.
Short-Circuit List Operators
"&&" and "||" are AND-OR list operators. "&&" executes the first
command, and then executes the second command if the exit status of the
first command is zero. "||" is similar, but executes the second command
if the exit status of the first command is nonzero. "&&" and "||" both
have the same priority.
Flow-Control Constructs (if, while, for, case)
The syntax of the if command is:
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, in "$@" 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:
break [num]
continue [num]
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 `|' 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.
Grouping Commands Together
Commands may be grouped by writing either
(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
Functions
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 the local
command. This should appear as the first statement of a function, and
the syntax is:
local [variable ...] [-]
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
return [exitstatus]
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.
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
name=value
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.
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 set built-in
command can also be used to set or reset them.
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.
$* 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 separate argument. If there are no
positional parameters, 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 arguments:
"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 built-in command, 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 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 wait built-in command reports completion of
the process.
$0 (zero) Expands to the name of the shell script if passed on the
command line, the name operand if given (with -c) or otherwise
argument 0 passed to the shell.
Special Variables
The following variables are set by the shell or have special meaning to
it:
CDPATH The search path used with the cd built-in.
EDITOR The fallback editor used with the fc built-in. If not set,
the default editor is ed(1).
FCEDIT The default editor used with the fc built-in.
HISTSIZE The number of previous commands that are accessible.
HOME The user's home directory, used in tilde expansion and as a
default directory for the cd built-in.
IFS Input Field Separators. This is initialized at startup to
<space>, <tab>, and <newline> in that order. This value
also applies if IFS is unset, but not if it is set to the
empty string. See the White Space Splitting section for
more details.
LINENO The current line number in the script or function.
MAIL The name of a mail file, that will be checked for the
arrival of new mail. Overridden by MAILPATH.
MAILPATH A colon (`:') separated list of file names, for the shell
to check for incoming mail. This variable overrides the
MAIL setting. There is a maximum of 10 mailboxes that can
be monitored at once.
OPTIND The index of the next argument to be processed by getopts.
This is initialized to 1 at startup.
PATH The default search path for executables. See the Path
Search section for details.
PPID The parent process ID of the invoked shell. This is set at
startup unless this variable is in the environment. A
later change of parent process ID is not reflected. A
subshell retains the same value of PPID.
PS1 The primary prompt string, which defaults to "$ ", unless
you are the superuser, in which case it defaults to "# ".
PS1 may include any of the following formatting sequences,
which are replaced by the given information:
\H This system's fully-qualified hostname (FQDN).
\h This system's hostname.
\u User name.
\W The final component of the current working
directory.
\w The entire path of the current working directory.
\$ Superuser status. "$" for normal users and "#" for
superusers.
\\ A literal backslash.
PS2 The secondary prompt string, which defaults to "> ". PS2
may include any of the formatting sequences from PS1.
PS4 The prefix for the trace output (if -x is active). The
default is "+ ".
Word Expansions
This clause describes the various expansions that are performed on words.
Not all expansions are performed on every word, as explained later.
Tilde expansions, parameter expansions, command substitutions, arithmetic
expansions, and quote removals that occur within a single word expand to
a single field. It is only field splitting or pathname expansion that
can create multiple fields from a single word. The single exception to
this rule is the expansion of the special parameter @ within double-
quotes, as was described above.
The order of word expansion is:
1. Tilde Expansion, Parameter Expansion, Command Substitution,
Arithmetic Expansion (these all occur at the same time).
2. Field Splitting is performed on fields generated by step (1) unless
the IFS variable is null.
3. Pathname Expansion (unless the -f option is in effect).
4. Quote Removal.
The `$' character is used to introduce parameter expansion, command
substitution, or arithmetic expansion.
Tilde Expansion (substituting a user's home directory)
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).
Parameter Expansion
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 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 `?' 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:
${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. 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.
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:
$(command)
or the backquoted version:
`command`
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 ( must be separated by whitespace to avoid ambiguity with arithmetic
expansion.
Arithmetic Expansion
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, 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
* / % + - << >> < <= > >= == != & ^ | && ||
Assignment operators
= += -= *= /= %= <<= >>= &= ^= |=
Conditional operator
? :
The result of the expression is substituted in decimal.
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.
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.
Pathname Expansion (File Name Generation)
Unless the -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 case
command.
Shell Patterns
A pattern consists of normal characters, which match themselves, and
meta-characters. The meta-characters are `*', `?', and `['. 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.
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 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
wctype(3)) may be specified by surrounding the name with `[:' and `:]'.
For example, `[[:alpha:]]' is a shell pattern that matches a single
letter. The character class may be complemented by making an exclamation
point (`!') the first character of the character class. A caret (`^')
has the same effect but is non-standard.
To include a `]' in a character class, make it the first character listed
(after the `!' or `^', if any). To include a `-', make it the first or
last character listed.
Built-in Commands
This section lists the built-in commands.
: A null command that returns a 0 (true) exit value.
. file The commands in the specified file are read and executed by the
shell. The return command may be used to return to the .
command's caller. If file contains any `/' characters, it is
used as is. Otherwise, the shell searches the PATH for the file.
If it is not found in the PATH, it is sought in the current
working directory.
[ A built-in equivalent of test(1).
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 built-in
command prints the names and values of all defined aliases (see
unalias). Alias values are written with appropriate quoting so
that they are suitable for re-input to the shell. Also see the
Aliases subsection.
bg [job ...]
Continue the specified jobs (or the current job if no jobs are
given) in the background.
bind [-aeklrsv] [key [command]]
List or alter key bindings for the line editor. This command is
documented in editrc(5).
break [num]
See the Flow-Control Constructs subsection.
builtin cmd [arg ...]
Execute the specified built-in command, cmd. This is useful when
the user wishes to override a shell function with the same name
as a built-in command.
cd [-L | -P] [-e] [directory]
cd - Switch to the specified directory, to the directory specified in
the HOME environment variable if no directory is specified or to
the directory specified in the OLDPWD environment variable if
directory is -. If directory does not begin with /, ., or ..,
then the directories listed in the CDPATH variable will be
searched for the specified directory. If CDPATH is unset, the
current directory is searched. The format 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 the CDPATH mechanism was used or if directory was -.
If the -P option is specified, .. is handled physically and
symbolic links are resolved before .. components are processed.
If the -L option is specified, .. is handled logically. This is
the default.
The -e option causes 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.
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 -e was given.
chdir A synonym for the cd built-in command.
command [-p] [utility [argument ...]]
command [-p] -v utility
command [-p] -V utility
The first form of invocation executes the specified utility,
ignoring shell functions in the search. If utility is a special
builtin, it is executed as if it were a regular builtin.
If the -p option is specified, the command search is performed
using a default value of PATH that is guaranteed to find all of
the standard utilities.
If the -v option is specified, 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 "alias name=value".
The -V option is identical to -v except for the output. It
prints "utility is description" where description is either the
path name to utility, a special shell builtin, a shell builtin, a
shell function, a shell keyword or an alias for value.
continue [num]
See the Flow-Control Constructs subsection.
echo [-e | -n] [string ...]
Print a space-separated list of the arguments to the standard
output and append a newline character.
-n Suppress the output of the trailing newline.
-e Process C-style backslash escape sequences. The echo
command understands the following character escapes:
\a Alert (ring the terminal bell)
\b Backspace
\c Suppress the trailing newline (this has the side-
effect of truncating the line if it is not the
last character)
\e The ESC character (ASCII 0x1b)
\f Formfeed
\n Newline
\r Carriage return
\t Horizontal tab
\v Vertical tab
\\ Literal backslash
\0nnn (Zero) The character whose octal value is nnn
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
export name=value
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 `?'. 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) 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:
readonly name=value
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] [-- 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.
Command Line Editing
When sh is being used interactively from a terminal, the current command
and the command history (see fc in Built-in Commands) can be edited using
vi-mode command line editing. This mode uses commands similar to a
subset of those described in the vi(1) man page. The command "set -o vi"
(or "set -V") enables vi-mode editing and places sh into vi insert mode.
With vi-mode enabled, sh can be switched between insert mode and command
mode by typing <ESC>. Hitting <return> while in command mode will pass
the line to the shell.
Similarly, the "set -o emacs" (or "set -E") command can be used to enable
a subset of emacs-style command line editing features.
ENVIRONMENT
The following environment variables affect the execution of sh:
ENV Initialization file for interactive shells.
LANG, LC_* Locale settings. These are inherited by children of the
shell, and is used in a limited manner by the shell
itself.
OLDPWD The previous current directory. This is used and updated
by cd.
PWD An absolute pathname for the current directory, possibly
containing symbolic links. This is used and updated by
the shell.
TERM The default terminal setting for the shell. This is
inherited by children of the shell, and is used in the
history editing modes.
Additionally, environment variables are turned into shell variables at
startup, which may affect the shell as described under Special Variables.
FILES
~/.profile User's login profile.
/etc/profile System login profile.
/etc/shells Shell database.
/etc/suid_profile Privileged shell profile.
EXIT STATUS
If the script cannot be found, the exit status will be 127; if it cannot
be opened for another reason, the exit status will be 126. Other 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 exit builtin is used with a numeric argument, it will
return the argument.
SEE ALSO
builtin(1), chsh(1), echo(1), ed(1), emacs(1), kill(1), printf(1),
pwd(1), test(1), vi(1), execve(2), getrlimit(2), umask(2), wctype(3),
editrc(5), shells(5)
HISTORY
A sh command, the Thompson shell, appeared in Version 1 AT&T UNIX. It
was superseded in Version 7 AT&T UNIX by the Bourne shell, which
inherited the name sh.
This version of sh was rewritten in 1989 under the BSD license after the
Bourne shell from AT&T System V Release 4 UNIX.
AUTHORS
This version of sh was originally written by Kenneth Almquist.
BUGS
The sh utility does not recognize multibyte characters other than UTF-8.
Splitting using IFS does not recognize multibyte characters.
FreeBSD 13.1-RELEASE-p6 July 6, 2020 FreeBSD 13.1-RELEASE-p6
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