How do I set a file's timestamp in perl?

You use the utime function documented in utime. By way of example, here's a little program that copies the read and write times from its first argument to all the rest of them. 

    if (@ARGV < 2) {
	die "usage: cptimes timestamp_file other_files ...\n";
    }
    $timestamp = shift;
    ($atime, $mtime) = (stat($timestamp))[8,9];
    utime $atime, $mtime, @ARGV;

Error checking is left as an exercise for the reader.

Note that utime currently doesn't work correctly with Win95/NT ports. A bug has been reported. Check it carefully before using it on those platforms.