Opcje wyszukiwania podręcznika man:
Lista stron man zaczynających się od znaku:
A   B   C   D   E   F   G   H   I   J   K   L   M   N   O   P   Q   R   S   T   U   V   W   X   Y   Z   ALPHA   NUM   OTHER   ALL
COMMAND(P)                 POSIX Programmer's Manual                COMMAND(P)

       command - execute a simple command

       command [-p] command_name [argument ...]

       command [ -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 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 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 com-

       On systems supporting the User Portability Utilities option,  the  com-
       mand  utility  also  shall provide information concerning how a command
       name is interpreted by the shell; see -v and -V.

       The command utility shall conform to the  Base  Definitions  volume  of
       IEEE Std 1003.1-2001, 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     (On systems supporting the User Portability  Utilities  option.)
              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  Shell  Execution Environment ), to
              invoke command_name, but do not invoke command_name.

               * Utilities, regular built-in utilities, command_names  includ-
                 ing  a  slash character, and any implementation-defined func-
                 tions that are found using the PATH variable (as described in
                 Command  Search and Execution ), shall be written as absolute

               * 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 definition.

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

       -V     (On systems supporting the User Portability  Utilities  option.)
              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 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 implementa-
                 tion-defined functions that are found using the PATH variable
                 (as  described  in  Command  Search and Execution ), shall be
                 identified as such and include the absolute pathname  in  the

               * Other shell functions shall be identified as functions.

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

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

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

               * Shell reserved words shall be identified as reserved words.

       The following operands shall be supported:

              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 com-

       LANG   Provide a default value for the  internationalization  variables
              that  are  unset  or  null.  (See the Base Definitions volume of
              IEEE Std 1003.1-2001, Section  8.2,  Internationalization  Vari-
              ables  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.

              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 arguments).

              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.

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

       PATH   Determine  the  search  path  used  during  the  command  search
              described  in 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

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

       Otherwise,  the exit status of command shall be that of the simple com-
       mand 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 func-
       tions 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 get-
       conf 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

       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  dis-
       tinguish  "failure to find a utility" from "invoked utility exited with
       an error indication". The value 127 was chosen because it is  not  com-
       monly  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:

              (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 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
       IEEE Std 1003.1-2001 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  direc-
           tory exactly once:

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

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

           #    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 func-
       tions to exist when it is invoked; this capability is not specified  by
       this  volume  of  IEEE Std 1003.1-2001,  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 unnecessary.

        * A  special  built-in  has  special  properties (see 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
       IEEE Std 1003.1-2001) when PATH is unset. At the very least, this  fea-
       ture  is  required to allow the script to access the correct version of
       getconf so that the  value  of  the  default  path  can  be  accurately

       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 addi-
       tion 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  applica-
       tion parsing reasons.


       Command  Search  and  Execution , Shell Execution Environment , Special
       Built-In Utilities , sh ,  type  ,  the  System  Interfaces  volume  of
       IEEE Std 1003.1-2001, exec

       Portions  of  this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
       --  Portable  Operating  System  Interface (POSIX), The Open Group Base
       Specifications Issue 6, Copyright (C) 2001-2003  by  the  Institute  of
       Electrical  and  Electronics  Engineers, Inc and The Open Group. 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 .

IEEE/The Open Group                  2003                           COMMAND(P)

Czas wygenerowania: 0.00013 sek.

Created with the man page lookup class by Andrew Collington.
Based on a C man page viewer by Vadim Pavlov
Unicode soft-hyphen fix (as used by RedHat) by Dan Edwards
Some optimisations by Eli Argon
Caching idea and code contribution by James Richardson

Copyright © 2003-2023
Hosted by Hosting