ps is one of the most variable of Unix commands. I doubt that what would work in my system would work in yours. For one thing, mine does not seem to have the 80-char limitation that you describe. Be that as it may, you could try setting the COLUMNS environment variable in your shell line, e.g.:

$ps_check = `COLUMNS=300 ps -ef | grep $pid.log`;
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(Untested.)

I agree with Nkuvu that this is much more of a Unix question than a Perl question; I think you'll likely get better advice if you asked this question in a forum devoted to your flavor of Unix.