*update* : bad link corrected

*update2* : reply to myself using B::Deparse => Re: strange usage of s/// -- I'm still confused :)

*update3* : problem solved, it's a Perl 5.14 and 5.16 bug.
Thanks, contributors, especially slms. As explained in slms's post(Re^2: strange usage of s///), Perl 5.18 behavior is correct :
Perl v5.18.1 handles them as one would expect: 
perl -MO=Deparse -e '$_="abcdef"; s/@{[s".."."gr]}\K$"//; print'
$_ = 'abcdef';
s[@{[s/.././gr];}\K$"][];
print $_;
-e syntax OK

[download]
perl -MO=Deparse -e '$_="abcdef"; s/@{[s".."."gr]}\K //; print'
$_ = 'abcdef';
s[@{[s/.././gr];}\K ][];
print $_;
-e syntax OK

[download]

With Perl 5.14 and 5.16, there is a bug and some quantum tunnelling in s/// (yep! ;):

perl -MO=Deparse -e '$_="abcdef"; s/@{[s".."."gr]}\K$"//; print'
$_ = 'abcdef';
s[@{[s/.././rg];}\K][$"];
print $_;
-e syntax OK

[download]
perl -MO=Deparse -e '$_="abcdef"; s/@{[s".."."gr]}\K //; print'
$_ = 'abcdef';
s[@{[s/.././rg];}][\\K ];
print $_;
-e syntax OK

[download]

original post:

Dear Monks,

Could you, please, help me to understand one mysterious golf solution posted by "tails" at http://golf.shinh.org/p.rb?Bisection . (problem: read line, eg "abcdef", and print bisection, ie "abc def")

This is not the best answer (shortest) but it seems very strange... Here is the code (http://golf.shinh.org/reveal.rb?Bisection/tails_1377006056&pl => http://golf.shinh.org/reveal.rb?Bisection/tails+%28%3F%29_1377006539&pl):

#!perl -pl
s/@{[s".."."gr]}\K$"//

[download]

*update* : why $" is different from literal space character in this regex? how this regex can add something to $_?

My other strange tests

$_="abcdef";
s/@{[s".."."gr]}/$& /;print  #  "...abcdef"

$_="abcdef";
s/@{[s".."."gr]}//;print     #  "...abcdef"

$_="abcdef";
s/@{[s".."."gr]}\K //;print  #  "\K def"

[download]

FYI, "tails" also wins the contest with:

#!perl -p
s/.(?0).|\K/ $&/

[download]

Nice usage of (?0), tails! :)

English is not my mother tongue.
Les tongues de ma mère sont "made in France".

In reply to strange usage of s/// [solved: Perl 5.14 and 5.16 bug] by brx

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