Well this is a Unix question instead of a Perl question. But depending on your flavor of Unix, you may be able to do something like my $ps_check = `ps -efww | grep $pid.log`;

From the manpage for ps on my system (OS X 10.4.1):

-w      Use 132 columns to display information, instead of the default
        which is your window size.  If the -w option is specified more
        than once, ps will use as many columns as necessary without
        regard for your window size.
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