Re: mysteries of regex substring matching (updated)

I think unpack is better for this as haukex has suggested, but here's a pure-regex solution:

Win8 Strawberry 5.8.9.5 (32)  Fri 01/15/2021 18:04:55
C:\@Work\Perl\monks
>perl -Mstrict -Mwarnings -MData::Dump=dd

my $s = q(AAAAbbbbCCCCddddXeeeeeeeeeeX);

my @caps = $s =~ m{ (?<! \A .{16}) \G .{4} | .* }xmsg;
dd \@caps;

^Z
["AAAA", "bbbb", "CCCC", "dddd", "XeeeeeeeeeeX", ""]
[download]

The trick is to have an unambiguous look-around anchor.

Update: Another variation:

Win8 Strawberry 5.8.9.5 (32)  Fri 01/15/2021 18:19:20
C:\@Work\Perl\monks
>perl -Mstrict -Mwarnings -MData::Dump=dd

my $s = q(AAAAbbbbCCCCddddXeeeeeeeeeeX);

my $n = 4;
my $m = 3;
my @caps = $s =~ m{ (?<! \A (?: .{$n}){$m}) \G .{$n} | .* }xmsg;
dd \@caps;

^Z
["AAAA", "bbbb", "CCCC", "ddddXeeeeeeeeeeX", ""]
[download]

Give a man a fish: <%-{-{-{-<

Comment on Re: mysteries of regex substring matching (updated) Select or Download Code

Replies are listed 'Best First'.

Re^2: mysteries of regex substring matching (explanation)
by LanX (Saint) on Jan 16, 2021 at 11:43 UTC

I'm sure we discussed this technique before, but I can't find it in the archives.

Do you remember a thread? :)

update

well I deciphered it in the meantime, it's not operating on match-groups but the /x /g ° modifier.

That'll repeat a search where the last match ended, and return all results in list context till it fails

  DB<139> p
0123456789abcdefghijklmnopqrstuvwxyz
  DB<139> x m{ .... }xg
0  0123
1  4567
2  '89ab'
3  'cdef'
4  'ghij'
5  'klmn'
6  'opqr'
7  'stuv'
8  'wxyz'
  DB<140>
[download]

with a negative look-behind (?<! ) we can filter out all matches after the initial 4

  DB<140> x m{ (?<! (?: .... ){4} ) .... }xg
0  0123
1  4567
2  '89ab'
3  'cdef'
  DB<141>
[download]

an or condition | helps matching after the fail.

  DB<142> x m{ (?<! (?: .... ){4} ) .... | .+ }xg
0  0123
1  4567
2  '89ab'
3  'cdef'
4  'ghijklmnopqrstuvwxyz'
  DB<143>
[download]

Cheers Rolf
_{(addicted to the Perl Programming Language :)

Wikisyntax for the Monastery}

°) thanks AnomalousMonk++ for spotting :)

[reply]
[d/l]
[select]


Don't ask to ask, just ask
	PerlMonks