Besides btrott's objections, setting a magic variable (the ever-lovable $/) that way is a recipe for debugging disaster!

Because the magic variables are relatively global, a change in one forgotten corner of your program somewhere can have far-reaching effects on other code. For example, if I were to write the (habitual) code thusly:

open (INPUT, $filename) || die "Can't open $filename: $!";
while (<INPUT>) {
    hack($_);
    slice($_);
    dice($_);
    vacuum_seal($_);
}
close INPUT || die "Wow, we're in for it now: $!";
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I assumed that the Input Record Separator ($/) was set to its default of "\n", as it almost always is. If I had called your subroutine earlier, it wouldn't be set to that.

Imagine the pain and suffering if that were in a module.

The solution is twofold. First, use local. This is one of the few places where it's absolutely necessary. Second (related to the first), place the entire code in a block -- that way, the local copy of $/ will be in effect only for that block, and the normal value will be in effect everywhere else.