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in reply to Re: Seeking clarification on possible bug in regex using \G and /gc
in thread Seeking clarification on possible bug in regex using \G and /gc

Breaks for me on perl 5.26. 
perl -E 'local $_ = "foo"; say "Start" if /\G foo/gcx; say "Mid" if /\
+G .*/gcx; say "End" if /\G \z/gcx'
Start
Mid

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Should instead print 
Start
Mid
End

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Here is a more extended item looking at pos as well. 
perl -E 'local $_ = "foo"; say "Start" if /\G foo/gcx; say pos; say "M
+id" if /\G .*/gcx; say pos; say "End" if /\G \z/gcx; say "At End" if 
+pos == length'
Start
3
Mid
3
At End

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

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Re^3: Seeking clarification on possible bug in regex using \G and /gc
by choroba (Cardinal) on Mar 14, 2018 at 23:52 UTC
    > Should instead print

    Why? Using perl -Mre=debug will show you your mistake: 

    ...
Matching REx "\G \z" against ""
   3 <foo> <>                |  1:GPOS(2)
   3 <foo> <>                |  2:EOS(3)
   3 <foo> <>                |  3:END(0)
Match possible, but length=0 is smaller than requested=1, failing!
Match failed

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    The length=1 request comes from the previously mentioned Repeated Patterns Matching a Zero-length Substring:

    The higher-level loops preserve an additional state between iterations: whether the last match was zero-length. To break the loop, the following match after a zero-length match is prohibited to have a length of zero. 

    ($q=q:Sq=~/;[c](.)(.)/;chr(-||-|5+lengthSq)`"S|oS2"`map{chr |+ord
}map{substrSq`S_+|`|}3E|-|`7**2-3:)=~y+S|`+$1,++print+eval$q,q,a,

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