Update: Sorry, I should have read the thread first, toolic said the same thing.

next if substr($fld0,-1,1) eq "X";
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is not exactly equivalent to

next if $fld0 =~ /X$/;
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since $ at the end of a regex is a bit special. From perlre #Metacharacters:

$        Match the end of the line (or before newline at the end)
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