Re^2: Issue with matching regex

It's even worse than that. When $var is emmpty, /$var/ matches anything only if there was no successful match before.

E.g. if you prepend this at the beginning of the script:

"abc" =~ /a/;
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it suddenly starts outputting "Outside if", because /$var/ runs the last successfully matched regex if there was any (see The empty pattern //). If you don't want this behaviour (and I bet you don't), never use a match with fully dynamic contents. You can change it to /(?:$var)/, so that the pattern doesn't get empty after interpolating the variable.

Update: There probably should be a perlcritic policy forbidding a potentially empty regex match.

map{substr$_->[0],$_->[1]||0,1}[\*||{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^*ARGV,3]

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Re^3: Issue with matching regex
by hippo (Archbishop) on Oct 20, 2022 at 08:32 UTC

The even better news is that the original if condition can be much simplified and by combining the first 2 regexen it can avoid the fully empty pattern into the bargain:

if ($line =~ /$var1|$var2/i && $check =~ /YES/i) { print "Inside if\n"
+;}
else {print "Outside if\n";}
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Of course if we still have $var1 = '' then it will still match but that's a question for KishKishore as to what they actually intend.

🦛

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Re^3: Issue with matching regex
by rsFalse (Chaplain) on Oct 20, 2022 at 11:54 UTC

if(($check =~ m/YES/i) and (($line =~ m/$var1/i) || ($line =~ m/$var2/
+i))) { print "Inside if\n";}
else {print "Outside if\n";}
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($check =~ m/Y/i)

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Re^3: Issue with matching regex
by Athanasius (Archbishop) on Oct 20, 2022 at 14:12 UTC

Thanks choroba,

I didn’t know that! This special case must have been implemented for a reason, but I can’t think what it could have been.

Using a non-capturing group to avoid this behaviour is a useful workaround.

The good news is that this special case doesn’t seem to be present in Raku:

23:48 >perl -wE "my $s = ''; say 'match1' if 'abc' =~ /b/; say 'match2
+' if 'adc =~ /(?:$s)/;"
match1
match2

23:55 >perl -wE "my $s = ''; say 'match1' if 'abc' =~ /b/; say 'match2
+' if 'adc =~ /$s/;"
match1

23:56 >raku -e "my Str $s = ''; say 'match1' if 'abc' ~~ /b/; say 'mat
+ch2' if 'adc' ~~ /$s/;"
match1
match2

23:56 >
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Cheers,

Athanasius <°(((>< contra mundum סתם עוד האקר של פרל,

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