Not really sure a) what this has to do with Perl or b) why you'd want to tar up one file, but here's the command.

tar xf /path/to/output/file /path/to/input/file
[download]

Typing man path would be a faster way to get this information.

"Perl makes the fun jobs fun
and the boring jobs bearable" - me

It is important to remember that when you tar in this way /path/to/input/file is stored in the tar so when you extract it, it will put it back in that very location. You probs what to ensure that you execute the tar command from the root of the files you want to tar and specify a full pathname to the tar file you are creating rather than the other way around.
--

Zigster

#!/usr/local/bin/perl -w
my $tarPath = "/path/to/place/tar/file";
my $fileName = "/path/to/file";
my $command = "tar xvf ";

$message = system ($command $tarPath $fileName);
if ($message == 0) {
    print "All done!\n";
} else {
    print "Whoops! $command gave exit error: $?\n";
}
[download]

MadraghRua
yet another biologist hacking perl.... ---------------------------------------------------- UPDATE
You might want to stick a my in front of $message to satisfy the -w switch - sorry!