And you can also use the 'open' command to run another command and redirect it's STDOUT. From the 'perlipc' manpage:

Using open() for IPC
       Perl's basic open() statement can also be used for unidirection
+al
       interprocess communication by either appending or prepending a 
+pipe
       symbol to the second argument to open().  Here's how to start s
+omething
       up in a child process you intend to write to:

           open(SPOOLER, "| cat -v | lpr -h 2>/dev/null")
                           || die "can't fork: $!";
           local $SIG{PIPE} = sub { die "spooler pipe broke" };
           print SPOOLER "stuff\n";
           close SPOOLER || die "bad spool: $! $?";

       And here's how to start up a child process you intend to read f
+rom:

           open(STATUS, "netstat -an 2>&1 |")
                           || die "can't fork: $!";
           while (<STATUS>) {
               next if /^(tcp|udp)/;
               print;
           }
           close STATUS || die "bad netstat: $! $?";
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For STDIN / STDOUT / STDERR at the same time you could use the IPC::Open3 module:

use IPC::Open3;
 $pid = open3(\*WTRFH, \*RDRFH, \*ERRFH,
                           'some cmd and args', 'optarg', ...);
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TMTOWTDI