IRIX Base Documentation 2001 May/SGI IRIX Base Documentation 2001 May.iso/usr/share/catman/u_man/cat1/command.z/command

Text File | 2001-04-17 | 14.5 KB | 331 lines

ccccoooommmmmmmmaaaannnndddd((((1111))))                                                          ccccoooommmmmmmmaaaannnndddd((((1111))))



NNNNAAAAMMMMEEEE
     ccccoooommmmmmmmaaaannnndddd - execute a simple command

SSSSYYYYNNNNOOOOPPPPSSSSIIIISSSS
     ccccoooommmmmmmmaaaannnndddd [----pppp] ccccoooommmmmmmmaaaannnndddd____nnnnaaaammmmeeee [aaaarrrrgggguuuummmmeeeennnntttt ...]
     ccccoooommmmmmmmaaaannnndddd [ ----vvvv | ----VVVV ] ccccoooommmmmmmmaaaannnndddd____nnnnaaaammmmeeee

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

     If the ccccoooommmmmmmmaaaannnndddd____nnnnaaaammmmeeee is the same as the name of one of the special built-
     in utilities, the special properties in the enumerated list below (See
     SSSSPPPPEEEECCCCIIIIAAAALLLL BBBBUUUUIIIILLLLTTTT----IIIINNNN PPPPRRRROOOOPPPPEEEERRRRTTTTIIIIEEEESSSS) will not occur. In every other respect, if
     ccccoooommmmmmmmaaaannnndddd____nnnnaaaammmmeeee is not the name of a function, the effect of ccccoooommmmmmmmaaaannnndddd will be
     the same as omitting ccccoooommmmmmmmaaaannnndddd.

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

OOOOPPPPTTTTIIIIOOOONNNNSSSS
     The ccccoooommmmmmmmaaaannnndddd utility supports the XBD specification, Utility Syntax
     Guidelines.

     The following options are supported:

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

     ----vvvv  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 ccccoooommmmmmmmaaaannnndddd____nnnnaaaammmmeeee.

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

             Shell functions, special built-in utilities, regular built-in
             utilities not associated with a PPPPAAAATTTTHHHH 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.

     ----VVVV  Write a string to standard output that indicates how the name given
         in the ccccoooommmmmmmmaaaannnndddd____nnnnaaaammmmeeee 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



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ccccoooommmmmmmmaaaannnndddd((((1111))))                                                          ccccoooommmmmmmmaaaannnndddd((((1111))))



         categories ccccoooommmmmmmmaaaannnndddd____nnnnaaaammmmeeee falls and include the information stated:

             Utilities, regular built-in utilities, and any implementation-
             dependent functions that are found using the PPPPAAAATTTTHHHH 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.

OOOOPPPPEEEERRRRAAAANNNNDDDDSSSS
     The following operands are supported:

     aaaarrrrgggguuuummmmeeeennnntttt       One of the strings treated as an argument to ccccoooommmmmmmmaaaannnndddd____nnnnaaaammmmeeee.

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

EEEENNNNVVVVIIIIRRRROOOONNNNMMMMEEEENNNNTTTT VVVVAAAARRRRIIIIAAAABBBBLLLLEEEESSSS
     The following environment variables affect the execution of command:

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

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

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

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

          "%s\n", <unspecified>

EEEEXXXXIIIITTTT SSSSTTTTAAAATTTTUUUUSSSS
     When the ----vvvv or ----VVVV options are specified, the following exit values are
     returned:

     0     Successful completion.






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ccccoooommmmmmmmaaaannnndddd((((1111))))                                                          ccccoooommmmmmmmaaaannnndddd((((1111))))



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

     Otherwise, the following exit values are returned:

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

     127   An error occurred in the ccccoooommmmmmmmaaaannnndddd utility or the utility specified
           by ccccoooommmmmmmmaaaannnndddd____nnnnaaaammmmeeee could not be found.

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

AAAAPPPPPPPPLLLLIIIICCCCAAAATTTTIIIIOOOONNNN UUUUSSSSAAAAGGGGEEEE
     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 ggggeeeettttccccoooonnnnffff; however, since
     ggggeeeettttccccoooonnnnffff may need to have the PPPPAAAATTTTHHHH 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 ccccoooommmmmmmmaaaannnndddd, eeeennnnvvvv, nnnnoooohhhhuuuupppp, ttttiiiimmmmeeee and xxxxaaaarrrrggggssss utilities have been specified to
     use exit code 111122227777 if an error occurs so that applications can distinguish
     "failure to find a utility" from "invoked utility exited with an error
     indication".  The value 111122227777 was chosen because it is not commonly used
     for other meanings; most utilities use small values for "normal error
     conditions" and the values above 111122228888 can be confused with termination due
     to receipt of a signal. The value 111122226666 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 111122226666 and 111122227777 cases.
     The distinction between exit codes 111122226666 and 111122227777 is based on KornShell
     practice that uses 111122227777 when all attempts to exec the utility fail with
     [EEEENNNNOOOOEEEENNNNTTTT], and uses 111122226666 when any attempt to exec the utility fails for any
     other reason.

     Since the ----vvvv and ----VVVV options of ccccoooommmmmmmmaaaannnndddd produce output in relation to the
     current shell execution environment, ccccoooommmmmmmmaaaannnndddd 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:




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ccccoooommmmmmmmaaaannnndddd((((1111))))                                                          ccccoooommmmmmmmaaaannnndddd((((1111))))



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

     it will not necessarily produce correct results. For example, when called
     with nnnnoooohhhhuuuupppp or an eeeexxxxeeeecccc 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 ccccoooommmmmmmmaaaannnndddd. 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 PPPPAAAATTTTHHHH search. So, for example, ccccoooommmmmmmmaaaannnndddd ----vvvv ttttrrrruuuueeee
     might yield ////bbbbiiiinnnn////ttttrrrruuuueeee 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 PPPPAAAATTTTHHHH, and so on.

EEEEXXXXAAAAMMMMPPPPLLLLEEEESSSS
     1.  Make a version of ccccdddd 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
     PPPPAAAATTTTHHHH, 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



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ccccoooommmmmmmmaaaannnndddd((((1111))))                                                          ccccoooommmmmmmmaaaannnndddd((((1111))))



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

SSSSPPPPEEEECCCCIIIIAAAALLLL BBBBUUUUIIIILLLLTTTT----IIIINNNN PPPPRRRROOOOPPPPEEEERRRRTTTTIIIIEEEESSSS
     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.

SSSSEEEEEEEE AAAALLLLSSSSOOOO
     sssshhhh((((1111)))),,,, ttttyyyyppppeeee((((1111))))....







































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