For completeness

> A "pure" regex approach is to use a positive look-behind assertion

use v5.12;
use warnings;
use Test::More;


say "Version: $]";


sub test {
    my ($msg, $str, $exp) = @_;

    my $pos = index($str, "*");
    die "NO POINTER <$msg> in <$str>" if $pos == -1;

    substr($str,$pos,1) = "";
    die "MULTIPLE POINTERS <$msg> in <$str>" if index($str,"*") >-1;

    no warnings 'experimental';         # no better category available
+ ???

    my $match = join "", ($str =~ m/^.{$pos}(*plb:(\d{0,254}))(\d+)/) 
+;

    is ($match,$exp,$msg);
}



test "In the middle", 'World 12*3456 Hello 789 ' =>   "123456" ;
test "At the start" , 'World *123456 Hello 789 ' =>   "123456" ;
test "At the end"   , 'World 12345*6 Hello 789 ' =>   "123456" ;
test "Before"       , 'Wo*rld 123456 Hello 789 ' =>   ""       ;
test "Right before" , 'World* 123456 Hello 789 ' =>   ""       ;
test "After"        , 'World 123456 *Hello 789 ' =>   ""       ;
test "Right after"  , 'World 123456* Hello 789 ' =>   ""       ;
test "In next Nr"   , 'World 123456 Hello 7*89 ' =>   "789"    ;
test "Nr at start"  , '*123456 Hello'            =>   "123456" ;
test "Nr at end"    , 'World 12345*6'            =>   "123456" ;
test "Pos at end"    , 'World 123456*'           =>   ""       ;


done_testing;

[download]

Version: 5.038002
ok 1 - In the middle
ok 2 - At the start
ok 3 - At the end
ok 4 - Before
ok 5 - Right before
ok 6 - After
ok 7 - Right after
ok 8 - In next Nr
ok 9 - Nr at start
ok 10 - Nr at end
ok 11 - Pos at end
1..11

[download]

Remarks

Unfortunately with variable length this still seems experimental with 5.38 ...

and I had to use a hard limit of 254 instead of * Strangely enough I couldn't find a dedicated warnings category and had to disable all "experimental" warnings locally.

Updates

had to fix tests because of C&P errors leading to multiple pointers, fixed test() to catch those errors.

Cheers Rolf
(addicted to the Perl Programming Language :)
see Wikisyntax for the Monastery

In reply to Re^2: How to capture backwards using regex? by LanX
in thread How to capture backwards using regex? by harangzsolt33

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