open F, "| some_shell_expression"; # open for writing
open F, "some_shell_expression |"; # open for reading

##</code><code>##

/usr/bin/mycommand < file

##</code><code>##

    my $cmd = "/usr/bin/mycommand < file";
    if ( system $cmd ) {
        warn $cmd .
          ($? == -1)
            ? " failed to execute: $!\n"
            : ($? & 127)
              ? sprintf "child died with signal %d, %s coredump\n",
                ($? & 127),
                ($? & 128)
                  ? 'with'
                  : 'without'
              : sprintf "child exited with value %d\n", $? >> 8;
    }