Check fs system command successfully completed in Perl?

Posted on 2011-03-21
Last Modified: 2012-05-11
If I run system command within Perl code, how can I check if it performed the process successfully?

Question by:Tolgar
1 Comment
LVL 48

Accepted Solution

Tintin earned 250 total points
ID: 35183595
From the command line type:

perldoc -f system

this will tell you

      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 complete.  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.

               Beginning with v5.6.0, 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.

                   @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 all possible 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 might inspect the value of "${^CHILD_ERROR_NATIVE}" with the W*() calls of the POSIX

               When the arguments get executed via the system shell, results and return codes will be subject to its quirks
               and capabilities.  See "`STRING`" in perlop and "exec" for details.

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