Regex help

[snacktime]

I think there is a better way of doing this, but I couldn't think of it. I have a string where I need to rewrite each occurence of [string] with the following:

__[username]__[string]__

There can be multiple instances of [string] in a line, and I don't want to match [string] a second time once it's been rewritten.

Here is what I am doing now. I know there has got to be a better way, but this does work.

my $prefix = "__" . $self->{user} . "__";
   my $suffix = "__";
   my %hash;
   my $c =0;
   my @contexts = sort {length $b <=> length $a} @list;
   foreach my $context (@contexts) {
      if($var_val =~s/($context?)/\@\@$c\@\@/g) {
         $hash{$c} = "$prefix$1$suffix";
         $c++;
      }
   }
   foreach my $key (keys %hash) {
      $var_val =~s/\@\@$key\@\@/$hash{$key}/g;
   }

[Roy Johnson]

So you've got multiple possible strings, and some of them might be substrings of others of them? If you combine them into one alternation, longest first, you should be ok:

my $super_regex = join '|', sort {length $b <=> length $a} map quoteme
+ta($_), @list;
$var_val =~ s/($super_regex)/$prefix$1$suffix/g;

Regexp::Optimizer might be of use if @list is long.

Update: added quotemeta as per ikegami's note.

[ikegami]

You forgot to use quotemeta, as shown in my reply.

[snacktime]

Ah that's exactly what I was looking for. Sorry for not explaining the issue correctly in my first post. Some of the strings being substrings of others was the real issue as you guessed.

[ikegami]

s///g won't search replaced text, as shown in the following snippet:

$search_for = '[string]';
$user       = '[user]';

local $_ = 'foo [string] bar [string] baz';


s/(\Q$search_for\E)/__${user}__${1}__/g;


print("$_\n");
# foo __[user]__[string]__ bar __[user]__[string]__ baz

You can use s///ge if you need to generate $user dynamically for each match.

[snacktime]

Silly me, I forgot what the problem was and mistated it. The problem is that the string I am searching for can exist as a substring of another element of @contexts, but I don't want it to match if it's already been rewritten.

For example in the list I am looping through, one element could be demo-outgoing, and a later element could be demo. I don't want the string demo in the already formatted string __user__demo-outgoing__ to be matched and rewritten again.

Does that make sense?

[ikegami]

So @context contains search strings? (This is why it's important to give a runable piece of code, including sample input. It takes the guessing out of the game.)

my @contexts = qw(
   demo-outgoing
   demo
);

local $_ = 'foo demo-outgoing bar';


my $regexp = join('|', map { quotemeta($_) } @contexts);
s/($regexp)/__user__${1}__/g;


print("$_\n");
# foo __user__demo-outgoing__ bar

[Joost]

what's in @list? Why does your code match "@@something@@" while your explenation states "[something]"?

how about this, assuming @strings is an array containing a list of "somethings" to replace:

for my $string (@strings) {
   $input =~ s/\[\Q$string\E\]/__[username]__[$string]__/;
}

This will replace every first occurence of every string in @strings with "__[username]__[$string]__"

update: see perlretut

[Jasper]

How not to ask a question? I don't understand one thing you're trying to do.