Does the text file contain a blank line?

rocroc:
Here's an example of behavior when processing a blank line or a line having empty or too few fields: an empty or missing field splits to an empty string or to undef. The reason for the seemingly spurious match is that an empty string or an undef becomes the // regex, which always matches!

>perl -wMstrict -le
"my $s = 'foo,,';
 ;;
 my ($field0, $field1, $field2, $field3) = split /,/, $s;
 print qq{field0 '$field0'  field1 '$field1'  field3 '$field3'};
 ;;
 if ('bar' =~ m{ $field1 }xms) { print qq{bar matches '$field1'} }
 if ('bar' =~ m{ $field3 }xms) { print qq{bar matches '$field3'} }
"
Use of uninitialized value $field3 in concatenation (.) or string ...
field0 'foo'  field1 ''  field3 ''
bar matches ''
Use of uninitialized value $field3 in regexp compilation ...
Use of uninitialized value $field3 in concatenation (.) or string ...
bar matches ''
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Note that without warnings (you are using warnings, aren't you?), this all proceeds quite silently:

>perl -Mstrict -le
"my $s = 'foo,,';
 ;;
 my ($field0, $field1, $field2, $field3) = split /,/, $s;
 print qq{field0 '$field0'  field1 '$field1'  field3 '$field3'};
 ;;
 if ('bar' =~ m{ $field1 }xms) { print qq{bar matches '$field1'} }
 if ('bar' =~ m{ $field3 }xms) { print qq{bar matches '$field3'} }
"
field0 'foo'  field1 ''  field3 ''
bar matches ''
bar matches ''
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