As you said, substr is the way to go. chop chops off one character, and not more than one. So, if you want to chop off 4 characters using chop, you need to chop 4 times. Either by duplicating the line, or by using a loop. You might want to bail out if the string is empty:

my $i = 4;
chop $string while $i -- && length $string;
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Or

my $i = 4;
1 while $i -- && defined chop $string;
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although the latter might want to chop an empty string (but only once).

Abigail