How can I see if a Perl hash already has a certain key

Question

I have a Perl script that is counting the number of occurrences of various strings in a text file  I want to be able to check if a certain string is not yet a key in the hash  Is there a better way of doing this altogether   Here is what I am doing   foreach  line   lines       if   line    m my regex                    string    1          if   string is not a key in  strings     strings  is an associative array                        strings  string    1                    else                        n     strings  string                 strings  string     n  1

User · Answer

I guess that this code should answer your question:

use strict;
use warnings;

my @keys = qw/one two three two/;
my %hash;
for my $key (@keys)
{
    $hash{$key}++;
}

for my $key (keys %hash)
{
   print "$key: ", $hash{$key}, "\n";
}

Output:

three: 1
one: 1
two: 2

The iteration can be simplified to:

$hash{$_}++ for (@keys);

(See $_ in perlvar.) And you can even write something like this:

$hash{$_}++ or print "Found new value: $_.\n" for (@keys);

Which reports each key the first time it’s found.

User · Answer

I believe to check if a key exists in a hash you just do  if  exists  strings  string               else

User · Answer

You can just go with   if   strings  string

User · Answer

I would counsel against using if   hash  key   since it will not do what you expect if the key exists but its value is zero or empty

User · Answer

Well  your whole code can be limited to   foreach  line   lines            strings  1    if  line    m my regex       If the value is not there     operator will assume it to be 0  and then increment to 1   If it is already there - it will simply be incremented

[perl] How can I see if a Perl hash already has a certain key?

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