Hello Monks,

I just run into quite an odd regex problem: I tried to compile a regex pattern with 'qr' which is case insensitive and contains a lookbehind assertion. If I have certain char combinations in my lookbehind expression, the regex engine throws the error: 

Variable length lookbehind not implemented in regex...

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Here some examples: 

my $pattern = "(?<!ss)abc";      # 'ss' in lookbehind
qr/$pattern/i;              # throws the error

my $pattern = "(?<!st)abc";     # 'st' in lookbehind 
qr/$pattern/i;              # throws the error

my $pattern =  "(?<!st)abc";    # 'st' in lookbehind
qr/$pattern/;              # this works fine since modifier 'i' is not
+ used

my $pattern =  "(?<!s)abc";    # 's' in lookbehind
qr/$pattern/i;             # this works fine

my $pattern =  "(?<!s[st])abc";    # 's[st]' in lookbehind
qr/$pattern/i;                  # this works, whereas these fail: (?<!
+s[s]),(?<!s[t])

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All patterns do what I'd expect if I don't compiled them.

Seems like the regex engine is interpreting the 'st' or 'ss' string as some meta-command, since no quantifier is used, that would cause a variable length.

I am using a new version of perl (v5.18.0). This problem did not occur in version v5.10.1.

Can anybody explain what is happening here? And is it maybe a known bug in perl version v5.18.0?

Thanks, WW

In reply to qr/STRING/ fails with certain lookbehind expressions by wiewa

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