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SH(1)			  BSD General Commands Manual			 SH(1)

     sh - command interpreter (shell)

     sh [-aCefnuvxIimqVEb] [+aCefnuvxIimqVEb] [-o option_name]
	[+o option_name] [command_file [argument ...]]
     sh -c [-aCefnuvxIimqVEb] [+aCefnuvxIimqVEb] [-o option_name]
	[+o option_name] command_string [command_name [argument ...]]
     sh -s [-aCefnuvxIimqVEb] [+aCefnuvxIimqVEb] [-o option_name]
	[+o option_name] [argument ...]

     sh is the standard command interpreter for the system.  The current ver
     sion of sh is in the process of being changed to conform with the POSIX
     1003.2 and 1003.2a specifications 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 (see ksh(1)).  Only features designated
     by POSIX, plus a few Berkeley extensions, are being incorporated into
     this shell.  We expect POSIX conformance by the time 4.4 BSD is released.
     This man page is not intended to be a tutorial or a complete specifica
     tion of the shell.

     The shell is a command that reads lines from either a file or the termi
     nal, interprets them, and generally executes other commands.  It is the
     program that is running when a user logs into the system (although a user
     can select a different shell with the chsh(1) command).  The shell imple
     ments 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 interpre
     tative language is common to both interactive and non-interactive use
     (shell scripts).  That is, commands can be typed directly to the running
     shell or can be put into a file and the file can be executed directly by
     the shell.

     If no args are present and if the standard input of the shell is con
     nected to a terminal (or if the -i flag is set), and the -c option is not
     present, 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 automati
     cally by the system when the user first logs in.  A login shell first
     reads commands from the files /etc/profile and .profile if they exist.
     If the environment variable ENV is set on entry to an interactive shell,
     or is set in the .profile of a login shell, the shell next 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 interactive shell inside the ENV file.  To
     set the ENV variable to some file, place the following line in your
     .profile of your home directory

	   ENV=$HOME/.shinit; export ENV

     substituting for .shinit any filename you wish.

     If command line arguments besides the options have been specified, then
     the shell treats the first argument as the name of a file from which to
     read commands (a shell script), and the remaining arguments are set as
     the positional parameters of the shell ($1, $2, etc).  Otherwise, the
     shell reads commands from its standard input.

   Argument List Processing
     All of the single letter options have a corresponding name that can be
     used as an argument to the -o option.  The set -o name is provided next
     to the single letter option in the description below.  Specifying a dash
     - turns the option on, while using a plus + disables the option.  The
     following options can be set from the command line or with the set
     builtin (described later).

	   -a allexport     Export all variables assigned to.

	   -c		    Read commands from the command_string operand
			    instead of from the standard input.  Special
			    parameter 0 will be set from the command_name
			    operand and the positional parameters ($1, $2,
			    etc.)  set from the remaining argument operands.

	   -C noclobber     Dont overwrite existing files with >.

	   -e errexit	    If not interactive, exit immediately if any
			    untested command fails.  The exit status of a com
			    mand is considered to be explicitly tested if the
			    command is used to control an if, elif, while, or
			    until; or if the command is the left hand operand
			    of an && or || operator.

	   -f noglob	    Disable pathname expansion.

	   -n noexec	    If not interactive, read commands but do not exe
			    cute them.	This is useful for checking the syntax
			    of shell scripts.

	   -u nounset	    Write a message to standard error when attempting
			    to expand a variable that is not set, and if the
			    shell is not interactive, exit immediately.

	   -v verbose	    The shell writes its input to standard error as it
			    is read.  Useful for debugging.

	   -x xtrace	    Write each command to standard error (preceded by
			    a + ) before it is executed.  Useful for debug

	   -I ignoreeof     Ignore EOFs from input when interactive.

	   -i interactive   Force the shell to behave interactively.

	   -m monitor	    Turn on job control (set automatically when inter

	   -s stdin	    Read commands from standard input (set automati
			    cally if no file arguments are present).  This
			    option has no effect when set after the shell has
			    already started running (i.e. with set).

	   -V vi	    Enable the built-in vi(1) command line editor
			    (disables -E if it has been set).

	   -E emacs	    Enable the built-in emacs(1) command line editor
			    (disables -V if it has been set).

	   -b notify	    Enable asynchronous notification of background job
			    completion.  (UNIMPLEMENTED for 4.4alpha)

   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 char
     acters that are special to the shell called operators.  There are two
     types of operators: control operators and redirection operators (their
     meaning is discussed later).  Following is a list of operators:

	   Control operators:
		 & && ( ) ; ;; | || 

	   Redirection operators:
		 < > >| << >> <& >& <<- <>

     Quoting is used to remove the special meaning of certain characters or
     words to the shell, such as operators, whitespace, or keywords.  There
     are three types of quoting: matched single quotes, matched double quotes,
     and backslash.

     A backslash preserves the literal meaning of the following character,
     with the exception of newline.  A backslash preceding a newline is
     treated as a line continuation.

   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 dollarsign ($), backquote (), and backslash
     (\).  The backslash inside double quotes is historically weird, and
     serves to quote only the following characters:
	   $  " \ .
     Otherwise it remains literal.

   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:

	   !	   elif    fi	   while   case
	   else    for	   then    {	   }
	   do	   done    until   if	   esac

     Their meaning is discussed later.

     An alias is a name and corresponding value set using the alias(1) builtin
     command.  Whenever a reserved word may occur (see above), and after
     checking for reserved words, the shell checks the word to see if it
     matches an alias.	If it does, it replaces it in the input stream with
     its value.  For example, if there is an alias called lf with the value
     ls -F, then the input:

	   lf foobar return

     would become

	   ls -F foobar return

     Aliases provide a convenient way for naive users to create shorthands for
     commands without having to learn how to create functions with arguments.
     They can also be used to create lexically obscure code.  This use is dis

     The shell interprets the words it reads according to a language, the
     specification of which is outside the scope of this man page (refer to
     the BNF in the POSIX 1003.2 document).  Essentially though, a line is
     read and if the first word of the line (or after a control operator) is
     not a reserved word, then the shell has recognized a 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

	   1.	Leading words of the form name=value are stripped off and
		assigned to the environment of the simple command.  Redirec
		tion operators and their arguments (as described below) are
		stripped off and saved for processing.

	   2.	The remaining words are expanded as described in the section
		called Expansions, and the first remaining word is consid
		ered the command name and the command is located.  The remain
		ing words are considered the arguments of the command.	If no
		command name resulted, then the name=value variable assign
		ments recognized in item 1 affect the current shell.

	   3.	Redirections are performed as described in the next section.

     Redirections are used to change where a command reads its input or sends
     its output.  In general, redirections open, close, or duplicate an exist
     ing reference to a file.  The overall format used for redirection is:

	   [n] redir-op file

     where redir-op is one of the redirection operators mentioned previously.
     Following is a list of the possible redirections.	The [n] is an optional
     number, as in 3 (not [3], that refers to a file descriptor.

	   [n]> file   Redirect standard output (or n) to file.

	   [n]>| file  Same, but override the -C option.

	   [n]>> file  Append standard output (or n) to file.

	   [n]< file   Redirect standard input (or n) from file.

	   [n1]<&n2    Duplicate standard input (or n1) from file descriptor

	   [n]<&-      Close standard input (or n).

	   [n1]>&n2    Duplicate standard output (or n1) to n2.

	   [n]>&-      Close standard output (or n).

	   [n]<> file  Open file for reading and writing on standard input (or

     The following redirection is often called a here-document.

	   [n]<< delimiter
		 here-doc-text ...

     All the text on successive lines up to the delimiter is saved away and
     made available to the command on standard input, or file descriptor n if
     it is specified.  If the delimiter as specified on the initial line is
     quoted, then the here-doc-text is treated literally, otherwise the text
     is subjected to parameter expansion, command substitution, and arithmetic
     expansion (as described in the section on Expansions).  If the operator
     is <<- instead of <<, then leading tabs in the here-doc-text are

   Search and Execution
     There are three types of commands: shell functions, builtin commands, and
     normal programs -- and the command is searched for (by name) in that
     order.  They each are executed in a different way.

     When a shell function is executed, all of the shell positional parameters
     (except $0, which remains unchanged) are set to the arguments of the
     shell function.  The variables which are explicitly placed in the envi
     ronment of the command (by placing assignments to them before the func
     tion 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 builtins are executed internally to the shell, without spawning a
     new process.

     Otherwise, if the command name doesnt match a function or builtin, 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
     "#!", so execve(2) returns ENOEXEC then) 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 com
     mands located in the parent shell will be remembered by the child.

     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 builtin command by that name.
     If a builtin command is not found, one of two things happen:

     1.   Command names containing a slash are simply executed without per
	  forming any searches.

     2.   The shell searches each entry in PATH in turn for the command.  The
	  value of the PATH variable should be a series of entries separated
	  by colons.  Each entry consists of a directory name.	The current
	  directory may be indicated 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 behaviour of other
     shell commands.  The paradigm is that a command exits with zero for nor
     mal or success, and non-zero for failure, error, or a false indication.
     The man page for each command should indicate the various exit codes and
     what they mean.  Additionally, the builtin commands return exit codes, as
     does an executed shell function.

     If a command consists entirely of variable assignments then the exit sta
     tus of the command is that of the last command substitution if any, oth
     erwise 0.

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

	simple command


	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.

     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 speci
     fied 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.  Other
     wise, 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

     Because pipeline assignment of standard input or standard output or both
     takes place before redirection, it can be modified by redirection.  For

	   $ 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
     next) to be executed sequentially; a & causes asynchronous execution of
     the preceding AND-OR-list.

     Note that unlike some other shells, each process in the pipeline is a
     child of the invoking shell (unless it is a shell builtin, in which case
     it executes in the current shell -- but any effect it has on the environ
     ment is wiped).

   Background Commands -- &
     If a command is terminated by the control operator ampersand (&), the
     shell executes the command asynchronously -- that is, the shell does not
     wait for the command to finish before executing the next command.

     The format for running a command in background is:

	   command1 & [command2 & ...]

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

   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 proceed 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 com
     mand, and then executes the second command iff the exit status of the
     first command is zero.  || is similar, but executes the second command
     iff the exit status of the first command is nonzero.  && and || both
     have the same priority.

   Flow-Control Constructs -- if, while, for, case
     The syntax of the if command is

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

     The syntax of the while command is

	   while list
	   do	list

     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

     The words are expanded, and then the list is executed repeatedly with the
     variable set to each word in turn.  do and done may be replaced with {
     and }.

     The syntax of the break and continue command is

	   break [ num ]
	   continue [ num ]

     Break terminates the num innermost for or while loops.  Continue contin
     ues with the next iteration of the innermost loop.  These are implemented
     as builtin commands.

     The syntax of the case command is

	   case word in
	   pattern) list ;;

     The pattern can actually be one or more patterns (see Shell Patterns
     described later), separated by | characters.

   Grouping Commands Together
     Commands may be grouped by writing either



	   { list; }

     The first of these executes the commands in a subshell.  Builtin commands
     grouped into a (list) will not affect the current shell.  The second form
     does not fork another shell so is slightly more efficient.  Grouping com
     mands together this way allows you to redirect their output as though
     they were one program:

	   { printf " hello " ; printf " world\n" ; } > greeting

     Note that } must follow a control operator (here, ;) so that it is
     recognized as a reserved word and not as another command argument.

     The syntax of a function definition is

	   name () command

     A function definition is an executable statement; when executed it
     installs a function named name and returns an exit status of zero.  The
     command is normally a list enclosed between { and }.

     Variables may be declared to be local to a function by using a local com
     mand.  This should appear as the first statement of a function, and the
     syntax is

	   local [variable | -] ...

     Local is implemented as a builtin command.

     When a variable is made local, it inherits the initial value and exported
     and readonly flags from the variable with the same name in the surround
     ing scope, if there is one.  Otherwise, the variable is initially unset.
     The shell uses dynamic scoping, so that if you make the variable x 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 any shell options that are changed via the set command inside the
     function to be restored to their original values when the function

     The syntax of the return command is

	   return [exitstatus]

     It terminates the currently executing function.  Return is implemented as
     a builtin 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 environ
     ment variables into shell variables.  New variables can be set using the


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

   Positional Parameters
     A positional parameter is a parameter denoted by a number (n > 0).  The
     shell sets these initially to the values of its command line arguments
     that follow the name of the shell script.	The set builtin can also be
     used to set or reset them.

   Special Parameters
     A special parameter is a parameter denoted by one of the following spe
     cial characters.  The value of the parameter is listed next to its char

     *		  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 posi
		  tional 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 builtin command, or implicitly by the

     $		  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 com
		  mand 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, Arith
	  metic Expansion (these all occur at the same time).

     2.   Field Splitting is performed on fields generated by step (1) unless
	  the IFS variable is null.

     3.   Pathname Expansion (unless set -f is in effect).

     4.   Quote Removal.

     The $ character is used to introduce parameter expansion, command substi
     tution, or arithmetic evaluation.

   Tilde Expansion (substituting a users 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 users home
     directory.  If the username is missing (as in ~/foobar), the tilde is
     replaced with the value of the HOME variable (the current users home

   Parameter Expansion
     The format for parameter expansion is as follows:


     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:


     The value, if any, of parameter is substituted.

     The parameter name or symbol can be enclosed in braces, which are
     optional except for positional parameters with more than one digit or
     when parameter is followed by a character that could be interpreted as
     part of the name.	If a parameter expansion occurs inside double-quotes:

     1.   Pathname expansion is not performed on the results of the expansion.

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

     In addition, a parameter expansion can be modified by using one of the
     following formats.

     ${parameter:-word}    Use Default Values.	If parameter is unset or null,
			   the expansion of word is substituted; otherwise,
			   the value of parameter is substituted.

     ${parameter:=word}    Assign Default Values.  If parameter is unset or
			   null, the expansion of word is assigned to parame
			   ter.  In all cases, the final value of parameter is
			   substituted.  Only variables, not positional param
			   eters or special parameters, can be assigned in
			   this way.

     ${parameter:?[word]}  Indicate Error if Null or Unset.  If parameter is
			   unset or null, the expansion of word (or a message
			   indicating it is unset if word is omitted) is writ
			   ten to standard error and the shell exits with a
			   nonzero exit status.  Otherwise, the value of
			   parameter is substituted.  An interactive shell
			   need not exit.

     ${parameter:+word}    Use Alternative 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 * 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

     ${parameter%word}	   Remove Smallest Suffix Pattern.  The word is
			   expanded to produce a pattern.  The parameter
			   expansion then results in parameter, with the
			   smallest portion of the suffix matched by the pat
			   tern deleted.

     ${parameter%%word}    Remove Largest Suffix Pattern.  The word is
			   expanded to produce a pattern.  The parameter
			   expansion then results in parameter, with the
			   largest portion of the suffix matched by the pat
			   tern deleted.

     ${parameter#word}	   Remove Smallest Prefix Pattern.  The word is
			   expanded to produce a pattern.  The parameter
			   expansion then results in parameter, with the
			   smallest portion of the prefix matched by the pat
			   tern deleted.

     ${parameter##word}    Remove Largest Prefix Pattern.  The word is
			   expanded to produce a pattern.  The parameter
			   expansion then results in parameter, with the
			   largest portion of the prefix matched by the pat
			   tern deleted.

   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:


     or (backquoted version):


     The shell expands the command substitution by executing command in a sub
     shell environment and replacing the command substitution with the stan
     dard 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 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 expan
     sion is as follows:


     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

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

   Pathname Expansion (File Name Generation)
     Unless the -f flag is set, file name generation is performed after word
     splitting is complete.  Each word is viewed as a series of patterns, sep
     arated 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 com

   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-

     An asterisk (*) matches any string of characters.	A question mark
     matches any single character.  A left bracket ([) introduces a charac
     ter 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 excla
     mation point the first character of the character class.

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

     This section lists the builtin commands which are builtin because they
     need to perform some operation that cant be performed by a separate pro
     cess.  In addition to these, there are several other commands that may be
     builtin for efficiency (e.g.  printf(1), echo(1), test(1), etc).


     true   A null command that returns a 0 (true) exit value.

     . file
	    The commands in the specified file are read and executed by the

     alias [name[=string ...]]
	    If name=string is specified, the shell defines the alias name with
	    value string.  If just name is specified, the value of the alias
	    name is printed.  With no arguments, the alias builtin prints the
	    names and values of all defined aliases (see unalias).

     bg [job] ...
	    Continue the specified jobs (or the current job if no jobs are
	    given) in the background.

     command [-p] [-v] [-V] command [arg ...]
	    Execute the specified command but ignore shell functions when
	    searching for it.  (This is useful when you have a shell function
	    with the same name as a builtin command.)

	    -p	   search for command using a PATH that guarantees to find all
		   the standard utilities.

	    -V	   Do not execute the command but search for the command and
		   print the resolution of the command search.	This is the
		   same as the type builtin.

	    -v	   Do not execute the command but search for the command and
		   print the absolute pathname of utilities, the name for
		   builtins or the expansion of aliases.

     cd -

     cd [-LP] [directory]
	    Switch to the specified directory (default HOME).  If an entry for
	    CDPATH appears in the environment of the cd command or the shell
	    variable CDPATH is set and the directory name does not begin with
	    a slash, then the directories listed in CDPATH will be searched
	    for the specified directory.  The format of CDPATH is the same as
	    that of PATH.  If a single dash is specified as the argument, it
	    will be replaced by the value of OLDPWD.  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 the argument is a single dash.  The -P option causes the
	    physical directory structure to be used, that is, all symbolic
	    links are resolved to their respective values.  The -L option
	    turns off the effect of any preceding -P options.

     echo [-n] args...
	    Print the arguments on the standard output, separated by spaces.
	    Unless the -n option is present, a newline is output following the

	    If any of the following sequences of characters is encountered
	    during output, the sequence is not output.	Instead, the specified
	    action is performed:

	    \b	    A backspace character is output.

	    \c	    Subsequent output is suppressed.  This is normally used at
		    the end of the last argument to suppress the trailing new
		    line that echo would otherwise output.

	    \f	    Output a form feed.

	    \n	    Output a newline character.

	    \r	    Output a carriage return.

	    \t	    Output a (horizontal) tab character.

	    \v	    Output a vertical tab.

		    Output the character whose value is given by zero to three
		    octal digits.  If there are zero digits, a nul character
		    is output.

	    \\	    Output a backslash.

	    All other backslash sequences elicit undefined behaviour.

     eval string ...
	    Concatenate all the arguments with spaces.	Then re-parse and exe
	    cute 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
	    builtin or function).  Any redirections on the exec command are
	    marked as permanent, so that they are not undone when the exec
	    command finishes.

     exit [exitstatus]
	    Terminate the shell process.  If exitstatus is given it is used as
	    the exit status of the shell; otherwise the exit status of the
	    preceding command is used.

     export name ...

     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 it is exported by writing

		  export name=value

	    With no arguments the export command lists the names of all
	    exported variables.  With the -p option specified the output will
	    be formatted suitably for non-interactive use.

     fc [-e editor] [first [last]]

     fc -l [-nr] [first [last]]

     fc -s [old=new] [first]
	    The fc builtin lists, or edits and re-executes, commands previ
	    ously 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 com
		   mand 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.


	    last   Select the commands to list or edit.  The number of previ
		   ous 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:

			  A positive number representing a command number;
			  command numbers can be displayed with the -l option.

			  A negative decimal number representing the command
			  that was executed number of commands previously.
			  For example, -1 is the immediately previous command.

		   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.

	    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, not to be confused with the Bell Labs
	    -derived getopt(1).

	    The first argument should be a series of letters, each of which
	    may be optionally followed by a colon to indicate that the option
	    requires an argument.  The variable specified is set to the parsed

	    The getopts command deprecates the older getopt(1) utility due to
	    its handling of arguments containing whitespace.

	    The getopts builtin may be used to obtain options and their argu
	    ments from a list of parameters.  When invoked, getopts places the
	    value of the next option from the option string in the list in the
	    shell variable specified by var and its index in the shell vari
	    able OPTIND.  When the shell is invoked, OPTIND is initialized to
	    1.	For each option that requires an argument, the getopts builtin
	    will place it in the shell variable OPTARG.  If an option is not
	    allowed for in the optstring, then OPTARG will be unset.

	    optstring is a string of recognized option letters (see
	    getopt(3)).  If a letter is followed by a colon, the option is
	    expected to have an argument which may or may not be separated
	    from it by white space.  If an option character is not found where
	    expected, getopts will set the variable var to a ?; getopts will
	    then unset OPTARG and write output to standard error.  By specify
	    ing a colon as the first character of optstring all errors will be

	    A nonzero value is returned when the last option is reached.  If
	    there are no remaining arguments, getopts will set var to the spe
	    cial option, --, otherwise, it will set var to ?.

	    The following code fragment shows how one might process the argu
	    ments for a command that can take the options [a] and [b], and the
	    option [c], which requires an argument.

		  while getopts abc: f
			  case $f in
			  a | b)  flag=$f;;
			  c)	  carg=$OPTARG;;
			  \?)	  echo $USAGE; exit 1;;
		  shift expr $OPTIND - 1

	    This code will accept any of the following as equivalent:

		  cmd -acarg file file
		  cmd -a -c arg file file
		  cmd -carg -a file file
		  cmd -a -carg -- file file

     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 the specified commands
	    from the hash table (unless they are functions) and then locates
	    them.  With the -v option, hash prints the locations of the com
	    mands as it finds them.  The -r option causes the hash command to
	    delete all the entries in the hash table except for functions.

     pwd [-LP]
	    builtin 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 builtin version of pwd will
	    continue to print the old name for the directory.  The -P option
	    causes the physical value of the current working directory to be
	    shown, that is, all symbolic links are resolved to their respec
	    tive values.  The -L option turns off the effect of any preceding
	    -P options.

     read [-p prompt] [-r] variable [...]
	    The prompt is printed if the -p option is specified and the stan
	    dard 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 word splitting above, and
	    the pieces are assigned to the variables in order.	At least one
	    variable must be specified.  If there are more pieces than vari
	    ables, 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.  The read builtin will indicate success unless
	    EOF is encountered on input, in which case failure is returned.

	    By default, unless the -r option is specified, the backslash \
	    acts as an escape character, causing the following character to be
	    treated literally.	If a backslash is followed by a newline, the
	    backslash and the newline will be deleted.

     readonly name ...

     readonly -p
	    The specified names are marked as read only, so that they cannot
	    be subsequently modified or unset.	The shell allows the value of
	    a variable to be set at the same time it is marked read only by

		  readonly name=value

	    With no arguments the readonly command lists the names of all read
	    only variables.  With the -p option specified the output will be
	    formatted suitably for non-interactive use.

     printf format [arguments ...]
	    printf formats and prints its arguments, after the first, under
	    control of the format.  The format is a character string which
	    contains three types of objects: plain characters, which are sim
	    ply copied to standard output, character escape sequences which
	    are converted and copied to the standard output, and format speci
	    fications, each of which causes printing of the next successive

	    The arguments after the first are treated as strings if the corre
	    sponding format is either b, c or s; otherwise it is evaluated as
	    a C constant, with the following extensions:

		     A leading plus or minus sign is allowed.
		     If the leading character is a single or double quote,
		      the value is the ASCII code of the next character.

	    The format string is reused as often as necessary to satisfy the
	    arguments.	Any extra format specifications are evaluated with
	    zero or the null string.

	    Character escape sequences are in backslash notation as defined in
	    ANSI X3.159-1989 (ANSI C).	The characters and their meanings
	    are as follows:

		  \a	  Write a  character.

		  \b	  Write a  character.

		  \f	  Write a  character.

		  \n	  Write a  character.

		  \r	  Write a  character.

		  \t	  Write a  character.

		  \v	  Write a  character.

		  \\	  Write a backslash character.

		  \num	  Write an 8-bit character whose ASCII value is the
			  1-, 2-, or 3-digit octal number num.

	    Each format specification is introduced by the percent character
	    (%).  The remainder of the format specification includes, in
	    the following order:

	    Zero or more of the following flags:

		    #	    A # character specifying that the value should
			    be printed in an alternative form.	For b, c,
			    d, and s formats, this option has no effect.  For
			    the o format the precision of the number is
			    increased to force the first character of the out
			    put string to a zero.  For the x (X) format, a
			    non-zero result has the string 0x (0X) prepended
			    to it.  For e, E, f, g, and G formats, the result
			    will always contain a decimal point, even if no
			    digits follow the point (normally, a decimal point
			    only appears in the results of those formats if a
			    digit follows the decimal point).  For g and G
			    formats, trailing zeros are not removed from the
			    result as they would otherwise be.

		    -	    A minus sign - which specifies left adjustment
			    of the output in the indicated field;

		    +	    A + character specifying that there should
			    always be a sign placed before the number when
			    using signed formats.

			  A space specifying that a blank should be left
			    before a positive number for a signed format.  A
			    + overrides a space if both are used;

		    0	    A zero 0 character indicating that zero-padding
			    should be used rather than blank-padding.  A -
			    overrides a 0 if both are used;

	    Field Width:
		    An optional digit string specifying a field width; if the
		    output string has fewer characters than the field width it
		    will be blank-padded on the left (or right, if the left-
		    adjustment indicator has been given) to make up the field
		    width (note that a leading zero is a flag, but an embedded
		    zero is part of a field width);

		    An optional period, ., followed by an optional digit
		    string giving a precision which specifies the number of
		    digits to appear after the decimal point, for e and f for
		    mats, or the maximum number of characters to be printed
		    from a string (b and s formats); if the digit string is
		    missing, the precision is treated as zero;

		    A character which indicates the type of format to use (one
		    of diouxXfwEgGbcs).

	    A field width or precision may be * instead of a digit string.
	    In this case an argument supplies the field width or precision.

	    The format characters and their meanings are:

	    diouXx	The argument is printed as a signed decimal (d or i),
			unsigned octal, unsigned decimal, or unsigned hexadec
			imal (X or x), respectively.

	    f		The argument is printed in the style [-]ddd.ddd where
			the number of ds after the decimal point is equal to
			the precision specification for the argument.  If the
			precision is missing, 6 digits are given; if the pre
			cision is explicitly 0, no digits and no decimal point
			are printed.

	    eE		The argument is printed in the style [-]d.dddedd
			where there is one digit before the decimal point and
			the number after is equal to the precision specifica
			tion for the argument; when the precision is missing,
			6 digits are produced.	An upper-case E is used for an
			E format.

	    gG		The argument is printed in style f or in style e (E)
			whichever gives full precision in minimum space.

	    b		Characters from the string argument are printed with
			backslash-escape sequences expanded.
			The following additional backslash-escape sequences
			are supported:

			\c	Causes sh to ignore any remaining characters
				in the string operand containing it, any
				remaining string operands, and any additional
				characters in the format operand.

			\0num	Write an 8-bit character whose ASCII value is
				the 1-, 2-, or 3-digit octal number num.

	    c		The first character of argument is printed.

	    s		Characters from the string argument are printed until
			the end is reached or until the number of characters
			indicated by the precision specification is reached;
			if the precision is omitted, all characters in the
			string are printed.

	    %		Print a %; no argument is used.

	    In no case does a non-existent or small field width cause trunca
	    tion of a field; padding takes place only if the specified field
	    width exceeds the actual width.

     set [{ -options | +options | -- }] arg ...
	    The set command performs three different functions.

	    With no arguments, it lists the values of all shell variables.

	    If options are given, it sets the specified option flags, or
	    clears them as described in the section called Argument List

	    The third use of the set command is to set the values of the
	    shells positional parameters to the specified args.  To change
	    the positional parameters without changing any options, use --
	    as the first argument to set.  If no args are present, the set
	    command will clear all the positional parameters (equivalent to
	    executing shift $#.)

     shift [n]
	    Shift the positional parameters n times.  A shift sets the value
	    of $1 to the value of $2, the value of $2 to the value of $3, and
	    so on, decreasing the value of $# by one.  If n is greater than
	    the number of positional parameters, shift will issue an error
	    message, and exit with return status 2.

     test expression

     [ expression ]
	    The test utility evaluates the expression and, if it evaluates to
	    true, returns a zero (true) exit status; otherwise it returns 1
	    (false).  If there is no expression, test also returns 1 (false).

	    All operators and flags are separate arguments to the test util

	    The following primaries are used to construct expression:

	    -b file	  True if file exists and is a block special file.

	    -c file	  True if file exists and is a character special file.

	    -d file	  True if file exists and is a directory.

	    -e file	  True if file exists (regardless of type).

	    -f file	  True if file exists and is a regular file.

	    -g file	  True if file exists and its set group ID flag is

	    -h file	  True if file exists and is a symbolic link.

	    -k file	  True if file exists and its sticky bit is set.

	    -n string	  True if the length of string is nonzero.

	    -p file	  True if file is a named pipe (FIFO).

	    -r file	  True if file exists and is readable.

	    -s file	  True if file exists and has a size greater than

	    -t file_descriptor
			  True if the file whose file descriptor number is
			  file_descriptor is open and is associated with a

	    -u file	  True if file exists and its set user ID flag is set.

	    -w file	  True if file exists and is writable.	True indicates
			  only that the write flag is on.  The file is not
			  writable on a read-only file system even if this
			  test indicates true.

	    -x file	  True if file exists and is executable.  True indi
			  cates only that the execute flag is on.  If file is
			  a directory, true indicates that file can be

	    -z string	  True if the length of string is zero.

	    -L file	  True if file exists and is a symbolic link.  This
			  operator is retained for compatibility with previous
			  versions of this program.  Do not rely on its exis
			  tence; use -h instead.

	    -O file	  True if file exists and its owner matches the effec
			  tive user id of this process.

	    -G file	  True if file exists and its group matches the effec
			  tive group id of this process.

	    -S file	  True if file exists and is a socket.

	    file1 -nt file2
			  True if file1 exists and is newer than file2.

	    file1 -ot file2
			  True if file1 exists and is older than file2.

	    file1 -ef file2
			  True if file1 and file2 exist and refer to the same

	    string	  True if string is not the null string.

	    s1 = s2	  True if the strings s1 and s2 are identical.

	    s1 != s2	  True if the strings s1 and s2 are not identical.

	    s1 < s2	  True if string s1 comes before s2 based on the ASCII
			  value of their characters.

	    s1 > s2	  True if string s1 comes after s2 based on the ASCII
			  value of their characters.

	    n1 -eq n2	  True if the integers n1 and n2 are algebraically

	    n1 -ne n2	  True if the integers n1 and n2 are not algebraically

	    n1 -gt n2	  True if the integer n1 is algebraically greater than
			  the integer n2.

	    n1 -ge n2	  True if the integer n1 is algebraically greater than
			  or equal to the integer n2.

	    n1 -lt n2	  True if the integer n1 is algebraically less than
			  the integer n2.

	    n1 -le n2	  True if the integer n1 is algebraically less than or
			  equal to the integer n2.

	    These primaries can be combined with the following operators:

	    ! expression  True if expression is false.

	    expression1 -a expression2
			  True if both expression1 and expression2 are true.

	    expression1 -o expression2
			  True if either expression1 or expression2 are true.

	    (expression)  True if expression is true.

	    The -a operator has higher precedence than the -o operator.

     times  Print the accumulated user and system times for the shell and for
	    processes run from the shell.  The return status is 0.

     trap [action signal ...]
	    Cause the shell to parse and execute action when any of the speci
	    fied signals are received.	The signals are specified by signal
	    number or as the name of the signal.  If signal is 0, the action
	    is executed when the shell exits.  action may be null, which cause
	    the specified signals to be ignored.  With action omitted or set
	    to - the specified signals are set to their default action.
	    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.	trap
	    without any arguments cause it to write a list of signals and
	    their associated action to the standard output in a format that is
	    suitable as an input to the shell that achieves the same trapping



	    List trapped signals and their corresponding action

		  trap	INT QUIT tstp 30

	    Ignore signals INT QUIT TSTP USR1

		  trap date INT

	    Print date upon receiving signal INT

     type [name ...]
	    Interpret each name as a command and print the resolution of the
	    command search.  Possible resolutions are: shell keyword, alias,
	    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 [-H | -S] [-a | -tfdscmlpn [value]]
	    Inquire about or set the hard or soft limits on processes or set
	    new limits.  The choice between hard limit (which no process is
	    allowed to violate, and which may not be raised once it has been
	    lowered) and soft limit (which causes processes to be signaled but
	    not necessarily killed, and which may be raised) is made with
	    these flags:

	    -H		set or inquire about hard limits

	    -S		set or inquire about soft limits.  If neither -H nor
			-S is specified, the soft limit is displayed or both
			limits are set.  If both are specified, the last one

	    The limit to be interrogated or set, then, is chosen by specifying
	    any one of these flags:

	    -a		show all the current limits

	    -t		show or set the limit on CPU time (in seconds)

	    -f		show or set the limit on the largest file that can be
			created (in 512-byte blocks)

	    -d		show or set the limit on the data segment size of a
			process (in kilobytes)

	    -s		show or set the limit on the stack size of a process
			(in kilobytes)

	    -c		show or set the limit on the largest core dump size
			that can be produced (in 512-byte blocks)

	    -m		show or set the limit on the total physical memory
			that can be in use by a process (in kilobytes)

	    -l		show or set the limit on how much memory a process can
			lock with mlock(2) (in kilobytes)

	    -p		show or set the limit on the number of processes this
			user can have at one time

	    -n		show or set the limit on the number files a process
			can have open at once

	    If none of these is specified, it is the limit on file size that
	    is shown or set.  If value is specified, the limit is set to that
	    number; otherwise the current limit is displayed.

	    Limits of an arbitrary process can be displayed or set using the
	    sysctl(8) utility.

     umask [mask]
	    Set the value of umask (see umask(2)) to the specified octal
	    value.  If the argument is omitted, the umask value is printed.

     unalias [-a] [name]
	    If name is specified, the shell removes that alias.  If -a is
	    specified, all aliases are removed.

     unset [-fv] name ...
	    The specified variables and functions are unset and unexported.
	    If -f or -v is specified, the corresponding function or variable
	    is unset, respectively.  If a given name corresponds to both a
	    variable and a function, and no options are given, only the vari
	    able is unset.

     wait [job]
	    Wait for the specified job to complete and return the exit status
	    of the last process in the job.  If the argument is omitted, wait
	    for all jobs to complete and the 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 Builtins) can be edited using vi-mode
     command-line editing.  This mode uses commands, described below, similar
     to a subset of those described in the vi man page.  The command set -o
     vi enables vi-mode editing and place sh into vi insert mode.  With vi-
     mode enabled, sh can be switched between insert mode and command mode.
     The editor is not described in full here, but will be in a later docu
     ment.  Its similar to vi: typing ESC will throw you into command VI
     command mode.  Hitting return while in command mode will pass the line
     to the shell.

     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.  Oth
     erwise the shell will return the exit status of the last command exe
     cuted, or if the exit builtin is used with a numeric argument, it will
     return the argument.

     HOME	Set automatically by login(1) from the users login directory
		in the password file (passwd(4)).  This environment variable
		also functions as the default argument for the cd builtin.

     PATH	The default search path for executables.  See the above sec
		tion Path Search.

     CDPATH	The search path used with the cd builtin.

     MAIL	The name of a mail file, that will be checked for the arrival
		of new mail.  Overridden by MAILPATH.

     MAILCHECK	The frequency in seconds that the shell checks for the arrival
		of mail in the files specified by the MAILPATH or the MAIL
		file.  If set to 0, the check will occur at each prompt.

     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.

     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	Output before each line when execution trace (set -x) is
		enabled, defaults to +	.

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

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

     HISTSIZE	The number of lines in the history buffer for the shell.

     PWD	The logical value of the current working directory.  This is
		set by the cd command.

     OLDPWD	The previous logical value of the current working directory.
		This is set by the cd command.

     PPID	The process ID of the parent process of the shell.



     csh(1), echo(1), getopt(1), ksh(1), login(1), printf(1), test(1),
     getopt(3), passwd(5), environ(7), sysctl(8)

     A sh command appeared in Version 1 AT&T UNIX.  It was, however, unmain
     tainable so we wrote this one.

     Setuid shell scripts should be avoided at all costs, as they are a sig
     nificant security risk.

     PS1, PS2, and PS4 should be subject to parameter expansion before being

BSD			       January 19, 2003 			   BSD

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