CODEWITHSUNDEEP
regexperl
alabamajack
alabamajack

Reputation: 662

Perl variable in regex for finding expression in hash

I have a big hash with a lot of elements.

%my_hash = ();
# filling of %my_hash automaticly
$my_variable;
# set the value of $my_variable within a loop

Now I want to find the value of $my_variablewithin %my_hash. I tried it with

if(grep {/$my_variable/} keys %my_hash){
    $my_new_variable = #here should be the element of %my_hash which makes the statement true
}

how to do that?

Edit: The problem is not the whole $my_variable will be find at %my_hash, e.g.

 $my_variable = astring
 $modules_by_path{"this_is_a_longer_astring"} = (something)

now I want to find this...

Upvotes: 0

Views: 155

Answers (3)

mpapec
mpapec

Reputation: 50637

If you're looking only for one particular key from %my_hash,

if (my ($my_new_variable) = grep /\Q$my_variable/, keys %my_hash) {

  ..
}

or

if (my @keys = grep /\Q$my_variable/, keys %my_hash) { .. }

if there are more keys which match specified regex. (use \Q prefix if $my_variable is not regex but literal string to be matched).

Upvotes: 2

Borodin
Borodin

Reputation: 126722

You can use grep, but you need to put it in scalar context to get the result you want. You also need to escape the contents of $my_variable if there's any chance that it contains any regex metacharacters.

This uses \Q to escape the non-alphanumeric characters, and leaves all the hash keys that match in @matching_keys. It's up to you to decide what to do if there's more than one match!

my @matching_keys = grep /\Q$my_variable/, keys %my_hash;

I suspect that there's a better way to do this. It's spoiling the whole point of hashes to search through them like that, and I think a better data design would help. But I can't say any more unless you describe your data and your application.

Upvotes: 1

Prawn
Prawn

Reputation: 59

if you want to match every key of your hash, you have to iterate through them in a loop as well. this is how i would do it, don't know if it is the most elegant way though:

#!/usr/bin/env perl
use strict;
use warnings;

my %hash = (
    foo => 1,
    bar => 1,
    baz => 1,
);

my $variable = "bar";
my $new_variable;

for my $key (keys %hash){
    if ($key =~ /$variable/){
        $new_variable = $hash{$key};
    }
}
print $new_variable, "\n";

also, always try to write stuff like that with use strict; it will spare you of many classic mistakes.

Upvotes: 0

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