in reply to Re^5: Regular expression
in thread Regular expression

my $test_string= '12345';

print "$1\n" if ($test_string=~ /(2)/g);  #Actually printed 2
print "$1\n" while ($test_string=~ /\G(\d)/g);# Printed every thing af
+ter 2 i.e 3,4,5

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Thanks Anomalous for this explanation. If I understand you correctly then essentially you mean \G is a kind of anchor (like ^ and $) but instead of having a fixed location, its position depends on where last match happened. As in my code above first print statement printed only 2 and then for next print statement pattern match started in the string from location next to 2 so 3,4,5 matched.I hope my understanding is correct so far.

Can you tell me what would be the scope of \G. Supposes in next print statement I use a different string, then also \G would will make pattern match to start from a position where it last matched in string one? what if second string is smaller than string in first print line and \G has a value greater than second string size?

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Re^7: Regular expression
by AnomalousMonk (Archbishop) on Nov 02, 2017 at 22:06 UTC
    ... what would be the scope of \G. Supposes in next print statement I use a different string, then also \G would will make pattern match to start from a position where it last matched in string one?

    Each individual string has an independent "position of end of last successful match" attribute that is returned by the pos built-in. The  \G regex operator (enabled by the  /g modifier) accesses this attribute of a string being matched to assert that matching in that string is continuing where previous matching in that string by any  m//g match left off. 

    c:\@Work\Perl\monks>perl -wMstrict -le
"my $s1 = 'foobarfeefiefoefum';
 $s1 =~ /foo/g;
 ;;
 my $s2 = '123456789';
 $s2 =~ /6/g;
 ;;
 print qq{A: pos in \$s1 '$s1' after successful match == }, pos $s1;
 print qq{B: pos in \$s2 '$s2' after successful match == }, pos $s2;
 ;;
 $s1 =~ /foe/g;
 print qq{C: pos in \$s1 '$s1' after successful match == }, pos $s1;
 print qq{D: pos in \$s2 '$s2' still == }, pos $s2;
"
A: pos in $s1 'foobarfeefiefoefum' after successful match == 3
B: pos in $s2 '123456789' after successful match == 6
C: pos in $s1 'foobarfeefiefoefum' after successful match == 15
D: pos in $s2 '123456789' still == 6

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    What would have happened if the second match against the  $s1 string had been  /\Gfoe/g instead? Or  /\Gbar/g instead? Try it and see! (See also the documentation concerning the effect of the  /c modifier in conjunction with  /g in a  m//gc match.)

    (Incidentally, what if  $test_string in your example code was  '12xxx345' and the match was  /(\d)/g (no \G) instead? What if it was  /\G(\d)/g as originally?)

    Give a man a fish:  <%-{-{-{-<

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