Tribblix: manual page: command.1

COMMAND(1) User Commands COMMAND(1)

NAME

command - execute a simple command

SYNOPSIS

/usr/bin/command
command [-p] command_name [argument]...

command [-v | -V] command_name

ksh93
command [-pvxV] [command_name [argument...]]

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 do not occur. In every
other respect, if command_name is not the name of a function, the
effect of command (with no options) are the same as omitting command.

The command utility also provides information concerning how a
command name is interpreted by the shell. See -v and -V.

ksh93
Without the -v or -V option, command executes command_name with
arguments specified by argument, suppressing the shell function
lookup that normally occurs. In addition, if command is a special
built-in command, the special properties are removed so that failures
do not cause the script that executes it to terminate.

If the -v or -V options are specified, command is equivalent to
whence(1).

OPTIONS

The following options are supported by /usr/bin/command:

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

-v
Writes a string to standard output that indicates the path or
command that is be used by the shell, in the current shell
execution environment to invoke command_name, but does not
invoke command_name.

o Utilities, regular built-in utilities, command_names
including a slash character, and any implementation-
provided functions that are found using the PATH
variable is written as absolute path names.

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

o An alias is written as a command line that
represents its alias definition.

o Otherwise, no output is written and the exit status
reflects that the name was not found.

-V
Writes a string to standard output that indicates how the name
specified in the command_name operand is interpreted by the
shell, in the current shell execution environment, but does not
invoke command_name. Although the format of this string is
unspecified, it indicates in which of the following categories
command_name falls and include the information stated:

o Utilities, regular built-in utilities, and any
implementation-provided functions that are found
using the PATH variable is identified as such and
include the absolute path name in the string.

o Other shell functions is identified as functions.

o Aliases are identified as aliases and their
definitions are included in the string.

o Special built-in utilities are identified as special
built-in utilities.

o Regular built-in utilities not associated with a
PATH search is identified as regular built-in
utilities.

o Shell reserved words are identified as reserved
words.

ksh93
The following options are supported by ksh93 command:

-p
Causes a default path to be searched rather than the one
defined by the value of PATH.

-v
Equivalent to:

whence command [argument ...]

-V
Equivalent to:

whence -v command [argument ...]

-x
If command fails because there are too many arguments, it is
invoked multiple times with a subset of the arguments on each
invocation. Arguments that occur prior to the first word that
expand to multiple arguments and arguments that occur after the
last word that expands to multiple arguments are passed on each
invocation. The exit status is the maximum invocation exit
status.

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.

EXAMPLES

Example 1: Making a Version of cd That Always Prints Out the New

Working Directory

The following example takes a version of cd that always prints out
the new working directory exactly once:

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

Example 2: Starting Off a secure shell script in Which the Script

Avoids Being Spoofed by Its Parent

The following example starts 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 can be present that would allow user
functions to exist when it is invoked. This capability is not
specified by this document, but it is not prohibited as an extension.
For example, the ENV variable precedes the invocation of the script
with a user startup script. Such a script could define functions to
spoof the application.

ENVIRONMENT VARIABLES

See environ(7) for descriptions of the following environment
variables that affect the execution of command: LANG, LC_ALL,
LC_CTYPE, LC_MESSAGES, and NLSPATH.

PATH
Determine the search path used during the command search,
except as described under the -p option.

EXIT STATUS

/usr/bin/command
When the -v or -V options are specified, the following exit values
are returned:

0
Successful completion.

>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 is that of the simple command
specified by the arguments to command.

ksh93
If command is invoked, the exit status of command is that of command.
Otherwise, it is one of the following:

0
command_name completed successfully.

>0
-v or -V has been specified and an error occurred.

126
command_name was found but could not be invoked.

127
command_name could not be found.

ATTRIBUTES