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Perl 5 version 22.0 documentation
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system

Perl functions A-Z | Perl functions by category | The 'perlfunc' manpage
  • system LIST

  • system PROGRAM LIST

    Does exactly the same thing as exec LIST , except that a fork is done first and the parent process waits for the child process to exit. Note that argument processing varies depending on the number of arguments. If there is more than one argument in LIST, or if LIST is an array with more than one value, starts the program given by the first element of the list with arguments given by the rest of the list. If there is only one scalar argument, the argument is checked for shell metacharacters, and if there are any, the entire argument is passed to the system's command shell for parsing (this is /bin/sh -c on Unix platforms, but varies on other platforms). If there are no shell metacharacters in the argument, it is split into words and passed directly to execvp , which is more efficient. On Windows, only the system PROGRAM LIST syntax will reliably avoid using the shell; system LIST , even with more than one element, will fall back to the shell if the first spawn fails.

    Perl will attempt to flush all files opened for output before any operation that may do a fork, but this may not be supported on some platforms (see perlport). To be safe, you may need to set $| ($AUTOFLUSH in English) or call the autoflush() method of IO::Handle on any open handles.

    The return value is the exit status of the program as returned by the wait call. To get the actual exit value, shift right by eight (see below). See also exec. This is not what you want to use to capture the output from a command; for that you should use merely backticks or qx//, as described in `STRING` in perlop. Return value of -1 indicates a failure to start the program or an error of the wait(2) system call (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 if you use the system PROGRAM LIST syntax. Again, see exec.

    Since SIGINT and SIGQUIT are ignored during the execution of system, if you expect your program to terminate on receipt of these signals you will need to arrange to do so yourself based on the return value.

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

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

    1.     if ($? == -1) {
    2.         print "failed to execute: $!\n";
    3.     }
    4.     elsif ($? & 127) {
    5.         printf "child died with signal %d, %s coredump\n",
    6.             ($? & 127),  ($? & 128) ? 'with' : 'without';
    7.     }
    8.     else {
    9.         printf "child exited with value %d\n", $? >> 8;
    10.     }

    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 SIGCHLD handler. See perlipc for details.

    Portability issues: system in perlport.