Recently we came across a script on our system that began hanging when we ported it to perl 5.6.0 (our system is currently running 5.005). We tracked it down and found that there was one regular expression that was causing the trouble. We've simplified the regex down to a one liner. 
perl -e '$_ = "a"; while (m/(\G|^)(a)/g) {print "[$2]\n";}'

[download]

We corrected the code to look like (in essense) the following (because (\G|^) is redundant): 
perl -e '$_ = "a"; while (m/(\G)(a)/g) {print "[$2]\n";}'

[download]

My question is, why does the first example hang under perl 5.6.0. Is there anybody with insight into what changed in the engine. Although the first regex is a bad example of what to do, this still seems like a bug in 5.6.0.

I'm posting this both to find an answer, and to invite more discussion on "\G" in regex's for newbies.



my @a=qw(random brilliant braindead); print $a[rand(@a)];

Edit: chipmunk 2001-05-15

In reply to regex (\G) vs. (^|\G) by Rhandom

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