The negative lookahead used in your first case m/(?!\.pl$)/) says:

"The NEXT thing cannot be ".pl". When it sees text ending in ".pl", the thing AFTER the ".pl is NOT ".pl", it is the end of line. So, the match succeeds.

The problem is that it is a ZERO WIDTH assertion, and does not require any text to match.

I would write the expression as : 

 print "$file\n" if  $file !~/\.pl$/

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Which works fine.

If you want to avoid the "." and "..", you need to check for those : 

next if $file =~/^\.\.?$|\.pl$/;

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        What is the sound of Perl? Is it not the sound of a wall that people have stopped banging their heads against?
              -Larry Wall, 1992

In reply to Re: Regex negative lookahead by NetWallah
in thread Regex negative lookahead by aeqr

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