lll.pl:
    sub longestLineLength {
      my $longestLen = undef;
      for my $l ( @_ ) {
        if ( length($l) > $longestLen ) {
          $longestLen = length($l);
       }
      }
      return $longestLen;
    }

test-01.pl:
    #!/usr/bin/perl
    require "lll.pl";
    open (TOP, "/usr/bin/top -bcS -n 1 |")
      || die "open pipe from top failed $!";
    print longestLineLength( <TOP> ) . "\n";

$ ./test-01.pl
80