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command(1)							    command(1)

NAME
     command - execute a simple command

SYNOPSIS
     command [-p] command_name [argument ...]
     command [ -v | -V ] command_name

DESCRIPTION
     The command utility causes the shell to treat the arguments as a simple
     command, suppressing the shell function lookup.

     If the command_name is the same as the name of one of the special built-
     in utilities, the special properties in the enumerated list below (See
     SPECIAL BUILT-IN PROPERTIES) will not occur. In every other respect, if
     command_name is not the name of a function, the effect of command will be
     the same as omitting command.

     The command utility also provides information concerning how a command
     name will be interpreted by the shell; see -v and -V.

OPTIONS
     The command utility supports the XBD specification, Utility Syntax
     Guidelines.

     The following options are supported:

     -p	 Perform the command search using a default value for PATH that is
	 guaranteed to find all of the standard utilities.

     -v	 Write a string to standard output that indicates the pathname or
	 command that will be used by the shell, in the current shell
	 execution environment, to invoke command_name.

	     Utilities, regular built-in utilities, command_names including a
	     slash character, and any implementation-dependent functions that
	     are found using the PATH variable will be written as absolute
	     pathnames.

	     Shell functions, special built-in utilities, regular built-in
	     utilities not associated with a PATH search, and shell reserved
	     words will be written as just their names.

	     An alias will be written as a command line that represents its
	     alias definition.

	     Otherwise, no output will be written and the exit status will
	     reflect that the name was not found.

     -V	 Write a string to standard output that indicates how the name given
	 in the command_name operand will be interpreted by the shell, in the
	 current shell execution environment.  Although the format of this
	 string is unspecified, it will indicate in which of the following

									Page 1

command(1)							    command(1)

	 categories command_name falls and include the information stated:

	     Utilities, regular built-in utilities, and any implementation-
	     dependent functions that are found using the PATH variable will
	     be identified as such and include the absolute pathname in the
	     string.

	     Other shell functions will be identified as functions.

	     Aliases will be identified as aliases and their definitions will
	     be included in the string.

	     Special built-in utilities will be identified as special built-in
	     utilities.

	     Regular built-in utilities not associated with a PATH search will
	     be identified as regular built-in utilities. (The term "regular"
	     need not be used.)

	     Shell reserved words will be identified as reserved words.

OPERANDS
     The following operands are supported:

     argument	    One of the strings treated as an argument to command_name.

     command_name   The name of a utility or a special built-in utility.

ENVIRONMENT VARIABLES
     The following environment variables affect the execution of command:

     PATH    Determine the search path used during the command search
	     described in Command Search and Execution, except as described
	     under the -p option.

STDOUT
     When the -v option is specified, standard output is formatted as:

	  "%s\n", <pathname or command>

     When the -V option is specified, standard output is formatted as:

	  "%s\n", <unspecified>

EXIT STATUS
     When the -v or -V options are specified, the following exit values are
     returned:

     0	   Successful completion.

									Page 2

command(1)							    command(1)

     >0	   The command_name could not be found or an error occurred.

     Otherwise, the following exit values are returned:

     126   The utility specified by command_name was found but could not be
	   invoked.

     127   An error occurred in the command utility or the utility specified
	   by command_name could not be found.

     Otherwise, the exit status of command will be that of the simple command
     specified by the arguments to command.

APPLICATION USAGE
     The order for command search allows functions to override regular built-
     ins and path searches. This utility is necessary to allow functions that
     have the same name as a utility to call the utility (instead of a
     recursive call to the function).

     The system default path is available using getconf; however, since
     getconf may need to have the PATH set up before it can be called itself,
     the following can be used:

	  command -p getconf _CS_PATH

     There are some advantages to suppressing the special characteristics of
     special built-ins on occasion. For example:

	  command exec > unwritable-file

     will not cause a non-interactive script to abort, so that the output
     status can be checked by the script.

     The command, env, nohup, time and xargs utilities have been specified to
     use exit code 127 if an error occurs so that applications can distinguish
     "failure to find a utility" from "invoked utility exited with an error
     indication".  The value 127 was chosen because it is not commonly used
     for other meanings; most utilities use small values for "normal error
     conditions" and the values above 128 can be confused with termination due
     to receipt of a signal. The value 126 was chosen in a similar manner to
     indicate that the utility could be found, but not invoked.	 Some scripts
     produce meaningful error messages differentiating the 126 and 127 cases.
     The distinction between exit codes 126 and 127 is based on KornShell
     practice that uses 127 when all attempts to exec the utility fail with
     [ENOENT], and uses 126 when any attempt to exec the utility fails for any
     other reason.

     Since the -v and -V options of command produce output in relation to the
     current shell execution environment, command is generally provided as a
     shell regular built-in. If it is called in a subshell or separate utility
     execution environment, such as one of the following:

									Page 3

command(1)							    command(1)

	  (PATH=foo command -v) nohup command -v

     it will not necessarily produce correct results. For example, when called
     with nohup or an exec function, in a separate utility execution
     environment, most implementations will not be able to identify aliases,
     functions or special built-ins.

     Two types of regular built-ins could be encountered on a system and these
     are described separately by command. The description of command search in
     Command Search and Execution allows for a standard utility to be
     implemented as a regular built-in as long as it is found in the
     appropriate place in a PATH search. So, for example, command -v true
     might yield /bin/true or some similar pathname. Other implementation-
     dependent utilities that are not defined by this specification might
     exist only as built-ins and have no pathname associated with them. These
     will produce output identified as (regular) built-ins. Applications
     encountering these will not be able to count on execing them, using them
     with nohup, overriding them with a different PATH, and so on.

EXAMPLES
     1.	 Make a version of cd that always prints out the new working directory
	 exactly once:

	 cd() { command cd "$@" >/dev/null pwd }

     2.	 Start off a "secure shell script" in which the script avoids being
	 spoofed by its parent:

	 IFS='
	 '
	 #    The preceding value should be <space><tab><newline>.
	 #    Set IFS to its default value.

	 \unalias -a
	 #    Unset all possible aliases.
	 #    Note that unalias is escaped to prevent an alias
	 #    being used for unalias.

	 unset -f command
	 #    Ensure command is not a user function.

	 PATH="$(command -p getconf _CS_PATH):$PATH"
	 #    Put on a reliable PATH prefix.
	 #    ...

     At this point, given correct permissions on the directories called by
     PATH, the script has the ability to ensure that any utility it calls is
     the intended one. It is being very cautious because it assumes that
     implementation extensions may be present that would allow user functions
     to exist when it is invoked; this capability is not specified by this
     specification, but it is not prohibited as an extension. For example, the

									Page 4

command(1)							    command(1)

     ENV variable precedes the invocation of the script with a user startup
     script. Such a script could define functions to spoof the application.

SPECIAL BUILT-IN PROPERTIES
     A syntax error in a special built-in utility may cause a shell executing
     that utility to abort, while a syntax error in a regular built-in utility
     will not cause a shell executing that utility to abort.  If a special
     built-in utility encountering a syntax error does not abort the shell,
     its exit value will be non-zero.

     Variable assignments specified with special built-in utilities will
     remain in effect after the built-in completes; this is not the case with
     a regular built-in or other utility.

SEE ALSO
     sh(1), type(1).

									Page 5

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