lanX's comment at Re: Going through a big file excellently explains the difference between how for slurps the whole lot into an array, but while does it line by line. The only comment I would add is why bother to have it open the files manually when it can be done implicitly? 
while (<>) {
}

[download]
does the job. Arguments other than the file(s) you want to process should be flags. In fact, you don't even need to write this code as it is automatically assumed when you run perl with flags such as -n or -p. See perlrun for more information.
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In reply to Re: Going through a big file [solved] by space_monk
in thread Going through a big file [solved] by Chuma

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