Sorry I mislead you with the line if($_ =~m/head/){}

It was just meant as an example regex. If you want to see how it works, with your test file try

 if($_ =~m/134/){  }
[download]

As others have pointed out, just to slurp a small file into an array, there are better ways than using <ARGV>. Your usage is Ok, but for small files you really don't need that type of code, as it was designed for line-by-line processing of huge files.