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       This  manual  page  is part of the POSIX Programmer's Manual.  The Linux implementation of
       this interface may differ (consult the corresponding Linux  manual  page  for  details  of
       Linux behavior), or the interface may not be implemented on Linux.


       command — execute a simple command


       command [−p] command_name [argument...]

       command [−p][−v|−V] command_name


       The  command  utility  shall  cause  the shell to treat the arguments as a simple command,
       suppressing the shell function lookup that is described in Section, Command Search
       and Execution, item 1b.

       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 at the beginning of Section 2.14, Special Built-
       In Utilities shall not occur. In every other respect, if command_name is not the name of a
       function, the effect of command (with no options) shall be the same as omitting command.

       When the −v or −V option is used, the command utility shall provide information concerning
       how a command name is interpreted by the shell.


       The  command utility shall conform to the Base Definitions volume of POSIX.1‐2008, Section
       12.2, Utility Syntax Guidelines.

       The following options shall be 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  (see
                 Section  2.12,  Shell Execution Environment), to invoke command_name, but do not
                 invoke command_name.

                  *  Utilities, regular built-in utilities,  command_names  including  a  <slash>
                     character, and any implementation-defined functions that are found using the
                     PATH  variable  (as  described  in  Section,  Command  Search   and
                     Execution), shall 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 shall be written  as
                     just their names.

                  *  An  alias  shall  be  written  as  a  command line that represents its alias

                  *  Otherwise, no output shall be written and the exit status shall 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  (see  Section 2.12, Shell Execution Environment), but do
                 not invoke command_name.  Although the format of this string is unspecified,  it
                 shall indicate in which of the following categories command_name falls and shall
                 include the information stated:

                  *  Utilities,  regular  built-in  utilities,  and  any   implementation-defined
                     functions  that  are  found using the PATH variable (as described in Section
           , Command Search and Execution), shall  be  identified  as  such  and
                     include the absolute pathname in the string.

                  *  Other shell functions shall be identified as functions.

                  *  Aliases shall be identified as aliases and their definitions included in the

                  *  Special  built-in  utilities  shall  be  identified  as   special   built-in

                  *  Regular  built-in  utilities  not  associated  with  a  PATH search shall be
                     identified as regular built-in utilities. (The term ``regular'' need not  be

                  *  Shell reserved words shall be identified as reserved words.


       The following operands shall be supported:

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

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


       Not used.




       The following environment variables shall affect the execution of command:

       LANG      Provide a default value for the internationalization variables that are unset or
                 null.  (See  the  Base  Definitions  volume  of   POSIX.1‐2008,   Section   8.2,
                 Internationalization   Variables  for  the  precedence  of  internationalization
                 variables used to determine the values of locale categories.)

       LC_ALL    If set to a non-empty string  value,  override  the  values  of  all  the  other
                 internationalization variables.

       LC_CTYPE  Determine  the  locale for the interpretation of sequences of bytes of text data
                 as characters (for example, single-byte as opposed to multi-byte  characters  in

                 Determine  the  locale  that should be used to affect the format and contents of
                 diagnostic messages written to standard error and informative  messages  written
                 to standard output.

       NLSPATH   Determine the location of message catalogs for the processing of LC_MESSAGES.

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




       When the −v option is specified, standard output shall be formatted as:

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

       When the −V option is specified, standard output shall be formatted as:

           "%s\n", <unspecified>


       The standard error shall be used only for diagnostic messages.






       When the −v or −V options are specified, the following exit values shall be returned:

        0    Successful completion.

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

       Otherwise, the following exit values shall be 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 shall be that of the simple command specified by the
       arguments to command.



       The following sections are informative.


       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 PATH

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

           command exec > unwritable-file

       does 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

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

       it does not necessarily produce correct results. For example, when called with nohup or an
       exec function, in a separate utility execution environment, most implementations  are  not
       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  Section,  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-defined
       utilities that are not defined by this volume of POSIX.1‐2008 might exist only  as  built-
       ins  and  have  no  pathname  associated  with  them.  These  produce output identified as
       (regular) built-ins. Applications encountering these are not  able  to  count  on  execing
       them, using them with nohup, overriding them with a different PATH, and so on.


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

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

        2. Start  off  a  ``secure shell script'' in which the script avoids being spoofed by its

               #    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="$(command −p getconf PATH):$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 volume of POSIX.1‐2008, but it is not prohibited  as  an  extension.
           For example, the ENV variable precedes the invocation of the script with a user start-
           up script. Such a script could define functions to spoof the application.


       Since command is a regular built-in utility it is always found prior to the PATH search.

       There is nothing in the description of command that implies the command line is parsed any
       differently from that of any other simple command. For example:

           command a | b ; c

       is  not  parsed  in any special way that causes '|' or ';' to be treated other than a pipe
       operator or <semicolon> or that prevents function lookup on b or c.

       The command utility is somewhat similar to the Eighth Edition shell builtin  command,  but
       since command also goes to the file system to search for utilities, the name builtin would
       not be intuitive.

       The command utility is most likely to be provided as a regular built-in. It is not  listed
       as a special built-in for the following reasons:

        *  The  removal of exportable functions made the special precedence of a special built-in

        *  A special  built-in  has  special  properties  (see  Section  2.14,  Special  Built-In
           Utilities)  that  were  inappropriate  for  invoking other utilities. For example, two
           commands such as:

               date > unwritable-file

               command date > unwritable-file

           would have entirely different results; in a non-interactive script, the  former  would
           continue  to  execute  the  next  command,  the  latter  would abort. Introducing this
           semantic difference along with suppressing functions was seen to be non-intuitive.

       The −p option is present because it is useful to be able to ensure a safe path search that
       finds  all  the  standard  utilities.  This  search might not be identical to the one that
       occurs through one of the exec functions (as defined in the System  Interfaces  volume  of
       POSIX.1‐2008) when PATH is unset. At the very least, this feature is required to allow the
       script to access the correct version of getconf so that the value of the default path  can
       be accurately retrieved.

       The  command  −v  and  −V  options  were added to satisfy requirements from users that are
       currently accomplished by three different historical  utilities:  type  in  the  System  V
       shell,  whence  in  the  KornShell, and which in the C shell. Since there is no historical
       agreement on how and what to accomplish here, the POSIX command utility was  enhanced  and
       the  historical  utilities were left unmodified.  The C shell which merely conducts a path
       search. The KornShell whence is more elaborate—in addition to the categories  required  by
       POSIX, it also reports on tracked aliases, exported aliases, and undefined functions.

       The  output  format  of  −V  was  left mostly unspecified because human users are its only
       audience.  Applications should not be written to care about this information; they can use
       the  output  of  −v to differentiate between various types of commands, but the additional
       information that may be emitted by the more verbose −V is not needed  and  should  not  be
       arbitrarily constrained in its verbosity or localization for application parsing reasons.




       Section, Command Search and Execution, Section 2.12, Shell Execution Environment,
       Section 2.14, Special Built-In Utilities, sh, type

       The Base Definitions volume of POSIX.1‐2008, Chapter  8,  Environment  Variables,  Section
       12.2, Utility Syntax Guidelines

       The System Interfaces volume of POSIX.1‐2008, exec


       Portions  of  this  text  are  reprinted  and  reproduced in electronic form from IEEE Std
       1003.1, 2013 Edition, Standard for Information Technology  --  Portable  Operating  System
       Interface  (POSIX),  The Open Group Base Specifications Issue 7, Copyright (C) 2013 by the
       Institute of Electrical and Electronics Engineers, Inc  and  The  Open  Group.   (This  is
       POSIX.1-2008  with  the  2013  Technical  Corrigendum  1  applied.)  In  the  event of any
       discrepancy between this version and the original IEEE and The Open  Group  Standard,  the
       original  IEEE  and The Open Group Standard is the referee document. The original Standard
       can be obtained online at .

       Any typographical or formatting errors that appear in this page are most  likely  to  have
       been  introduced  during  the conversion of the source files to man page format. To report
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