in reply to Re^4: How to remove underscore at the end of the line?
in thread How to remove underscore at the end of the line?

Instead of $prefix =~ s/_$//;, maybe try this: 
my $newfile = $prefix . $suffix;
$newfile =~ s/_$//;
rename "$dir/$file", "$dir/$newfile";

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In Section Seekers of Perl Wisdom