Translating Perl Regular Expression syntax

[jfreets2]

I am new to reqular expressions with perl and I was wondering if someone could help explain the difference between using parenthesis around a regular expression and using (?

Also any translation on the following syntax would be appreciated.

(?{ $_{test} = $^N })

Thanks

Jason

 

[Kirsle]

When you use parenthesis, whatever was matched from inside of them gets put into $1, $2, $3, etc., but with the ?: in front, the matched value isn't put into those.

$var = "23:45:02";

if ($var =~ /(\d\d):(\d\d):(\d\d)/) {
   # $1 = 23
   # $2 = 45
   # $3 = 02
}

if ($var =~ /(\d\d):[COLOR=red](?:\d\d)[/color]:(\d\d)/) {
   # $1 = 23
   # $2 = 02
   # there is no $3
}

-------------
Cuvou.com | The NEW Kirsle.net

 

[jfreets2]

Thank you very much! That is exactly what I needed to know. What about the syntax below. Can you help me translate this also. How is (? used. Is this still part of a regular expression? It looks like $_{test} is perl syntax?

(?{ $_{test} = $^N })

Jason

 

[Kirsle]

A quick copy/paste from perlretut concerning $^N:

so that if the regexp matched, e.g., $2 would contain 'cd' or 'ef'. For convenience, perl sets $+ to the string held by the highest numbered $1, $2, ... that got assigned (and, somewhat related, $^N to the value of the $1, $2, ... most-recently assigned; i.e. the $1, $2, ... associated with the rightmost closing parenthesis used in the match).

$_{test} is, I'm assuming, using $_ as a hash and using the key "test" from it.

Alright, after scrolling much further through perlretut, I found some example snippits:

    $x = "abcdef";
    $x =~ /abc(?{print "Hi Mom!";})def/; # matches,
                                         # prints 'Hi Mom!'
    $x =~ /aaa(?{print "Hi Mom!";})def/; # doesn't match,
                                         # no 'Hi Mom!'

Pay careful attention to the next example:

    $x =~ /abc(?{print "Hi Mom!";})ddd/; # doesn't match,
                                         # no 'Hi Mom!'
                                         # but why not?

So, the (?{...}) syntax executes Perl code directly within the regular expression.

Now looking back at the one you posted, it sets $_{test} to be the last $1,$2,$3,...,$n variable matched in the regexp.



-------------
Cuvou.com | The NEW Kirsle.net

 

[jfreets2]

That is awesome! That helps a lot thank you. I have one more question if you have time. If I have a hash that contains several keys, when I call "join" using "keys" it creates a list of the key values divided by a string character correct? Such as key1 "|" Key2 "|" Key3 etc. I am having trouble translating the following:

join("|",
keys %MyHash,
map { my $c = $_;
$c =~ s/(\w)/$1./g;
( quotemeta $c, $_ ) }
sort { length $b <=> length $a }
values %MyHash)