Re^2: Regular Expression: search two times for the same number of any signs (updated)

[Anonymous Monk]

Hi Hauke,

I am trying to fully understand all the new things. One question to your construct "for"

print "$_ =>\n" 
  for qw/ 1 12 123/;

is working fine. I like this style. But I can not combine it with an if or multiple lines.

{print "$_ =>\n" if $_=/1/ }
  for qw/ 1 12 123/;

gives me floowing error message: "Missing $ on loop variable at ./test3.pl line 2." and I can not understand, what is mean by this error meassage.

[haukex]

Hi Anonymous,

You can't use more than one statement modifier like for or if at a time (and I think that if you were able to, it would lead to more hard-to-understand code). If your code gets more complex you should instead use a normal for loop:

for my $n (qw/1 12 123 234/) {
    print "$n =>\n" if $n=~/1/;
}

(Ok, there is a way to do what you want, but legibility begins to suffer if it gets longer: /1/ and print "$_ =>\n" for qw/1 12 123 234/;)

Update: I should add that I was golfing a little bit in my example code, and that compressed style is not necessarily something one should strive to use in production code ;-)

Regarding the other question about (??{ }), that's documented along with (?{ }) in perlre. The oversimplified explanation is that the code inside (??{...}) is evaluated and its return value embedded as part of the regular expression (but make sure to read the docs). So in my regex, the code '.{'.length($2).'}' takes the length of the string matched in between the first set of x's (x(.*)x), and then generates an expression like .{N} (where N is the length), so if the input were x12345x67890x, the regular expression it is matched against is x.*x.{5}x.

Hope this helps,
-- Hauke D

Updated wordings a little bit.

[Anonymous Monk]

Hi Hauke,

Many many thanks for your explainations and tips !!!!!
Took a while to understand, read and try out ... I really learned thinks , that are a complet new level of perl for me !

Thanks