Referencing hash keys with a variable in perl

Question

I am trying to create a Perl script that allows me access a hash key/value by using a variable.

The code below is a very high level example of script does. Is there any way to reference the key of the hash with a variable? It looks like the $hash_exmp{$temp_var} is not being accepted.

my %hash_exmp = (
    $key_1 => "file1",
    $key_2 => "file2",
    $key_3 => "file3",
);

for($i = 1; $i <= 3; $i++){
    for($j = 1; $j <= 3; $j++){     
        print $j;            
        $temp_var = "key_${i}";
        print $hash_exmp{$temp_var};
    };
};

You've got a bunch of issues with this code (which would be highlighted if you use strict; use warnings;) which might explain the problem you are having. I don't know if they are the cause of your real problem or if your attempt to create a minimal reproducible example is just showing a different set of problems. — Quentin
– Quentin, Commented Oct 1, 2018 at 16:36
Did you mean $key_1 => "file1" or rather key_1 => "file1" ? — Håkon Hægland
– Håkon Hægland, Commented Oct 1, 2018 at 16:49
If you are trying to use a variable to store a variable name, that is a bad idea. — mob
– mob, Commented Oct 1, 2018 at 16:50
The issue was making my keys as variables when I changed them to string names it works, thanks! — tarkan
– tarkan, Commented Oct 1, 2018 at 17:09

Andrey · Accepted Answer · 2018-10-01 17:16:07Z

2

If I understand correctly what you are trying to do, you want something like this:

my %hash_exmp = (
    'key_1' => "file1",
    'key_2' => "file2",
    'key_3' => "file3",
);
for(my $i = 1; $i <= 3; $i++){
    print $hash_exmp{'key_'.$i} . "\n";
}

answered Oct 1, 2018 at 17:16

Andrey

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1 Comment

ikegami Over a year ago

And for(my $i = 1; $i <= 3; $i++) can be simplified to for my $i (1..3)

tarkan · Accepted Answer · 2018-10-01 17:11:06Z

0

The issue was making my keys as variables when I changed them to string names it works. In other words I changed from $key1 => "file1" to key1 => "file1"

answered Oct 1, 2018 at 17:11

tarkan

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1 Comment

zdim Over a year ago

You can use a variable for a key in a hash, my %h = ($key_name => 1) but that variable must be defined beforehand (my $key_name = 'id';) and then it will be evaluated and your "actual" key is that (the string 'id' in this example). Then you can work with it using a variable as well, $h{$var}, as long as that $var evaluates to the string 'id', for $h{id} (may drop quotes for a hash key when it's a clean literal). If you don't know whether a key exists for a string that a variable evaluates to then you can check, if (exists $h{$var}) ... .

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