Run a separate program

Daftar Isi

• system LIST

• system PROGRAM LIST

  Does exactly the same thing as exec LIST, except that a fork isdone first and the parent process waits for the child process toexit. Note that argument processing varies depending on thenumber of arguments. If there is more than one argument in LIST,or if LIST is an array with more than one value, starts the programgiven by the first element of the list with arguments given by therest of the list. If there is only one scalar argument, the argumentis checked for shell metacharacters, and if there are any, theentire argument is passed to the system's command shell for parsing(this is /bin/sh -c on Unix platforms, but varies on otherplatforms). If there are no shell metacharacters in the argument,it is split into words and passed directly to execvp, which ismore efficient.

  Beginning with v5.6.0, Perl will attempt to flush all files opened foroutput before any operation that may do a fork, but this may not besupported on some platforms (see perlport). To be safe, you may needto set $| ($AUTOFLUSH in English) or call the autoflush() methodof IO::Handle on any open handles.

  The return value is the exit status of the program as returned by thewait call. To get the actual exit value, shift right by eight (seebelow). See also exec. This is not what you want to use to capturethe output from a command; for that you should use merely backticks orqx//, as described in `STRING` in perlop. Return value of -1indicates a failure to start the program or an error of the wait(2) systemcall (inspect $! for the reason).

  If you'd like to make system (and many other bits of Perl) die on error,have a look at the autodie pragma.

  Like exec, system allows you to lie to a program about its name ifyou use the system PROGRAM LIST syntax. Again, see exec.

  Since SIGINT and SIGQUIT are ignored during the execution ofsystem, if you expect your program to terminate on receipt of thesesignals you will need to arrange to do so yourself based on the returnvalue.

   @args = ("command", "arg1", "arg2");
   
   system(@args) == 0
   
   or die "system @args failed: $?"
   

  If you'd like to manually inspect system's failure, you can check allpossible failure modes by inspecting $? like this:

   if ($? == -1) {
   
   print "failed to execute: $!\n";
   
   }
   
   elsif ($? & 127) {
   
   printf "child died with signal %d, %s coredump\n",
   
   ($? & 127),  ($? & 128) ? 'with' : 'without';
   
   }
   
   else {
   
   printf "child exited with value %d\n", $? >> 8;
   
   }
   

  Alternatively, you may inspect the value of ${^CHILD_ERROR_NATIVE}with the W*() calls from the POSIX module.

  When system's arguments are executed indirectly by the shell, results and return codes are subject to its quirks.See `STRING` in perlop and exec for details.

  Since system does a fork and wait it may affect a SIGCHLDhandler. See perlipc for details.

  Portability issues: system in perlport.