If you're going to do that often, and you can't have two cities with the same zip code, you can reverse the hash like this: my %reversed = reverse %zips; and then try exists $reversed{$zip}. Or you can grep on the values instead of the keys: grep { $_ eq $zip } values %zips;

Yes, it worked:


use strict;
use warnings;


my $zip = '01234';


 my %zips = (
                  "City One" => "04321",
          "City Two" => "01234",
         );

 my ($zip_match) = grep { $_ eq $zip } values %zips;

 print "\n $zip_match\n"; # 01234
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Can "grep" take a condition, like only assign to "$zip_match" if it is true?

Without parens on the LHS you'll call grep in scalar context and get the number of matches returned.

Only 0 matches is false.

But you should really take reverse into consideration to create an inverted hash.

Cheers Rolf

_{(addicted to the Perl Programming Language and ☆☆☆☆ :)}

Can "grep" take a condition, like only assign to "$zip_match" if it is true?

In the statement
    my ($zip_match) = grep { $_ eq $zip } values %zips;
the condition grep takes is  $_ eq $zip and it matches in list context, so it returns nothing (the empty list) if there is no match and assigns nothing to  $zip_match which retains the uninitialized value (i.e., undef) with which it was created.

In the OPed code, if  $zip is not any value of the hash,  $zip_match will not be defined:

c:\@Work\Perl\monks>perl -wMstrict -le
"my $zip = '99999';
 ;;
 my %zips = ('City One' => '04321',  'City Two' => '01234');
 ;;
 my ($zip_match) = grep { $zips{$_} eq $zip } keys %zips;
 print qq{'$zip' not found} if not defined $zip_match;
"
'99999' not found
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Update: The result of the grep operation (one or more matches vs. none) can also be tested directly:

c:\@Work\Perl\monks>perl -wMstrict -le
"my $zip = '01234';
 ;;
 my %zips = ('City One' => '04321',  'City Two' => '01234');
 ;;
 if (my ($zip_match) = grep { $zips{$_} eq $zip } keys %zips) {
   print qq{'$zip' located in '$zip_match'};
   }
 else {
   print qq{'$zip' not found};
   }
"
'01234' located in 'City Two'
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