Useless use of hash element in void context

basm101 has asked for the wisdom of the Perl Monks concerning the following question:

Hi
I am trying to assign single key-value pairs to a hash and something is going very wrong...I get the error messages Useless use of hash element in void context and Useless use of a variable in void context.

    open(INFILE,$infile) or die "Can't open $infile\n";
    print "opened $infile\n";<STDIN>;
    while(<INFILE>){
    
        if(/(\s+)(\d+)(\.)(\s+)([A-Z]{2})(\s+)([A-Z]{5})/){
# this matches certain lines in my data files
        $number++;
        print "$2=>$5\n"; # this works and prints my key and value tha
+t I want
        $hash_codes{$2}=>$5;#useless
        }
    }
[download]

Is the problem that I can't use $2 and $5 from my pattern match in this way ? I tried assigning like this:

$key = $2;
$value = $5;
$hash{$key}=>$value;
[download]

but no joy either. Please help !

Thanks
basm101

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Re: Useless use of hash element in void context by tachyon (Chancellor) on Sep 25, 2003 at 10:32 UTC
The => operator aka the FAT COMMA is a synonym for a comma so Perl sees your code as: `$hash_codes{$2},$5 # thus the useless use of hash element in void context. # there is also a useless use of scalar in void context as well. # you want $hash_codes{$2} = $5 # this is normal usage of => %hash = ( key1 => 'val1', key2 => 'val2' ); # which parses the same as: %hash = ( 'key1', 'val1', 'key2', 'val2' );` [download] The => is SYNTACTIC SUGAR to make hash assignments look spiffy.....It also lets you pass strinct and not bother to quote the LHS as shown cheers tachyon s&&rsenoyhcatreve&&&s&n.+t&"$'$`$\"$\&"&ee&&y&srve&&d&&print	[reply] [d/l]
Re: Useless use of hash element in void context by broquaint (Abbot) on Sep 25, 2003 at 10:32 UTC
The problem is that you're trying to use the 'fat comma' (`=>`) to assign to the hash, where in actual fact you just want the plain assignment operator e.g `$hash_codes{$2} = $5;` [download] The 'fat comma' behaves just like the normal comma operator but stringifies its left-hand argument and if its left-hand argument is a bareword it is exempt from `strict`. See. the `perlop` manpage for more information on the assignment and 'fat comma' operators. HTH `_________ broquaint`	[reply] [d/l]