open FH, "foo" or die "Can't open foo: $!";
    while (<FH>) {
        ## current line is in $_, process it
    }
    close FH or warn "Error closing foo: $!";

##</code><code>##

    while (<>) {
        ## line is in $_
    }

##</code><code>##

    $ process.pl foo.txt bar.txt baz.txt