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SH(1)                   FreeBSD General Commands Manual                  SH(1)

NAME
     sh - command interpreter (shell)

SYNOPSIS
     sh [-/+abCEefIimnPpsTuVvx] [-/+o longname] [-c string] [arg ...]

DESCRIPTION
     The sh utility is the standard command interpreter for the system.  The
     current version of sh is in the process of being changed to conform with
     the IEEE Std 1003.2 (``POSIX.2'') specification for the shell.  This
     version has many features which make it appear similar in some respects
     to the Korn shell, but it is not a Korn shell clone like pdksh.  Only
     features designated by POSIX, plus a few Berkeley extensions, are being
     incorporated into this shell.  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 reads commands from the file named in ENV.  Therefore, a user should
     place commands that are to be executed only at login time in the .profile
     file, and commands that are executed for every shell inside the ENV file.
     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 .shinit
     the filename desired:

           ENV=$HOME/.shinit; 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).

     -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 ! operator.  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.

     -f noglob
             Disable pathname expansion.

     -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).

     -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 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) to
             standard error before it is executed.  Useful for debugging.

     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 three types of quoting: matched 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).

     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.

   Reserved Words
     Reserved words are words that have special meaning to the shell and are
     recognized at the beginning of a line and after a control operator.  The
     following are reserved words:

           !        {        }        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.  Whenever a reserved word may occur (see above), and after
     checking for reserved words, the shell checks the word to see if it
     matches an alias.  If it does, it replaces it in the input stream with
     its value.  For example, if there is an alias called ``lf'' with the
     value ``ls -F'', then the input

           lf foobar

     would become

           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.
     They can also be used to create lexically obscure code.  This use is
     discouraged.

     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 reserved word, 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.  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.  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)) the shell will interpret the program in a subshell.  The child
     shell will reinitialize itself in this case, so that the effect will be
     as if a new shell had been invoked to handle the ad-hoc shell script,
     except that the location of hashed commands located in the parent shell
     will be remembered by the child (see the description of the hash built-in
     command below).

     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 environment 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 128 plus the
     signal number.  Signal numbers are defined in the header file
     <sys/signal.h>.

   Complex Commands
     Complex commands are combinations of simple commands with control
     operators or reserved words, together creating a larger complex command.
     More generally, a command is one of the following:

           simple command

           pipeline

           list or compound-list

           compound command

           function definition

     Unless otherwise stated, the exit status of a command is that of the last
     simple command executed by the command.

   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.

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

     If the reserved word ! does not precede the pipeline, the exit status is
     the exit status of the last command specified in the pipeline.
     Otherwise, the exit status is the logical NOT of the exit status of the
     last command.  That is, if the last command returns zero, the exit status
     is 1; if the last command returns greater than zero, the exit status is
     zero.

     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.

     Note that unlike some other shells, sh executes each process in the
     pipeline as a child of the sh process.  Shell built-in commands are the
     exception to this rule.  They are executed in the current shell, although
     they do not affect its environment when used in pipelines.

   Background Commands (&)
     If a command is terminated by the control operator ampersand (`&'), the
     shell executes the command 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.

   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 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 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.  The exit code of the case
     command is the exit code of the last command executed in the list or zero
     if no patterns were matched.

   Grouping Commands Together
     Commands may be grouped by writing either

           (list)

     or

           { list; }

     The first form executes the commands in a subshell.  Note that built-in
     commands thus executed do not affect the current shell.  The second form
     does not fork 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.

     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 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 previous
     nested function, sourced script, or shell instance, in that order.  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
     is called a variable.  When starting up, the shell turns all the
     environment variables into shell variables.  New variables can be set
     using the form

           name=value

     Variables set by the user must have a name consisting solely of
     alphabetics, numerics, and underscores.  The first letter of a variable
     name must not be numeric.  A parameter can also be denoted by a number or
     a special character as explained below.

   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
     A special parameter is a parameter denoted by a special one-character
     name.  The special parameters recognized by the sh shell of FreeBSD 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.

     $0      (zero) Expands to the name of the shell or shell script.

   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 evaluation.

   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 quoted string, and characters in
     embedded arithmetic expansions, command substitutions, and variable
     expansions, are 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.   Pathname expansion is not performed on the results of the expansion.

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

     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.

     ${#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 in a
     subshell environment 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.

   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, and quote removal.

     Next, the shell treats this as an arithmetic expression and substitutes
     the value of the expression.

   White Space Splitting (Field Splitting)
     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.

     The shell treats each character of the IFS variable as a delimiter and
     uses the delimiters to split the results of parameter expansion and
     command substitution into fields.

   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 both Pathname Expansion 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 range of characters may be specified
     using a minus sign.  The character class may be complemented by making an
     exclamation point (`!') the first character of the character class.

     To include a `]' in a character class, make it the first character listed
     (after the `!', if any).  To include a `-', make it the first or last
     character listed.

   Built-in Commands
     This section lists the commands which are built-in because they need to
     perform some operation that cannot be performed by a separate process.
     In addition to these, built-in versions of essential utilities are
     provided for efficiency.

     :       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.

     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.

     bind [-aeklrsv] [key [command]]
             List or alter key bindings for the line editor.  This command is
             documented in editrc(5).

     cd [-L | -P] [directory]
             Switch to the specified directory, or to the directory specified
             in the HOME environment variable if no directory is specified.
             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 this is
             different from the name that the user gave.  These may be
             different either because the CDPATH mechanism was used or because
             a symbolic link was crossed.

             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.

     chdir   A synonym for the cd built-in command.

     command [-p] [utility [argument ...]]

     command [-v | -V] [utility]
             The first form of invocation executes the specified utility as a
             simple command (see the Simple Commands section).

             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.

     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 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 environment 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.

     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.  Entries which have not been
             looked at since the last cd command are marked with an asterisk;
             it is possible for these entries to be invalid.

             With arguments, the hash command removes 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.

     local [variable ...] [-]
             See the Functions subsection.

     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 of 1 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.

     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] [-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.  If there are zero positional parameters, shifting
             does not do anything.

     test    A built-in equivalent of test(1).

     times   Print the amount of time spent executing the shell and its
             children.  The first output line shows the user and system times
             for the shell 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 is another way to
             request the default action, for compatibility reasons this usage
             is not recommended though.  When the shell forks off a subshell,
             it resets trapped (but not ignored) signals to the default
             action.  The trap command has no effect on signals that were
             ignored on entry to the shell.

             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 [-HSabcdflmnpstuvw] [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.

             -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.

             -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.

             -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 the specified job to complete and return the exit status
             of the last process in the job.  If the argument is omitted, wait
             for all jobs to complete and return an exit status of zero.

   Commandline 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:

     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 starting directory of sh.

     IFS           Input Field Separators.  This is normally set to <space>,
                   <tab>, and <newline>.  See the White Space Splitting
                   section for more details.

     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 environment setting
                   overrides the MAIL setting.  There is a maximum of 10
                   mailboxes that can be monitored at once.

     PATH          The default search path for executables.  See the Path
                   Search section for details.

     PS1           The primary prompt string, which defaults to ``$ '', unless
                   you are the superuser, in which case it defaults to ``# ''.

     PS2           The secondary prompt string, which defaults to ``> ''.

     PS4           The prefix for the trace output (if -x is active).  The
                   default is ``+ ''.

     TERM          The default terminal setting for the shell.  This is
                   inherited by children of the shell, and is used in the
                   history editing modes.

EXIT STATUS
     Errors that are detected by the shell, such as a syntax error, will cause
     the shell to exit with a non-zero exit status.  If the shell is not an
     interactive shell, the execution of the shell file will be aborted.
     Otherwise the shell will return the exit status of the last command
     executed, or if the 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), expr(1), getopt(1),
     pwd(1), test(1), vi(1), execve(2), getrlimit(2), umask(2), editrc(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.

FreeBSD 11.0-PRERELEASE         January 8, 2010        FreeBSD 11.0-PRERELEASE

NAME | SYNOPSIS | DESCRIPTION | ENVIRONMENT | EXIT STATUS | SEE ALSO | HISTORY | AUTHORS | BUGS

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