How do I check if a key exists in a hash in Perl?

Question

I want to check if parameter $PGkey is equal to a key with the same name inside a hash table. Further, I want to do it in a format as close to this as possible:

while(<PARAdef>) {
    my($PGkey, $PGval) = split /\s+=\s+/;
    if($PGkey == $hash{$PGkey}) {
        print PARAnew "$PGkey = $hash{$PGkey}->[$id]\n";
    } else {
        print PARAnew "$PGkey = $PGval\n";
    }
}

Is there a simple way to do it?

Answer 1

Using the conditional operator lets you factor out the common code in that if/else statement:

while ( <PARAdef> ) {
    chomp;
    my ($PGkey, $PGval) = split /\s+=\s+/;
    print "$PGkey = ",
        $PGval eq $hash{$PGkey}[$id] ? $hash{$PGkey}[$id] : $PGval, "\n";
}

Or if you just misstated the problem and really want to use $hash{$PGkey}[$id] if $hash{$PGkey} exists and fall back to $PGval if it doesn't, then you can say

while ( <PARAdef> ) {
    chomp;
    my ($PGkey, $PGval) = split /\s+=\s+/;
    print "$PGkey = ",
        $PGkey ne "def" and exists $hash{$PGkey} ?
            $hash{$PGkey}[$id] : $PGval, "\n";
}

A quick note, you seem to be using the old bareword style filehandles. The new (if ten years old can be considered new) lexical filehandles are superior in every way:

open my $PARAdef, "<", $filename
    or die "could not open $filename: $!";

Answer 2

Your question's kind of obscure, but the way to check for hash key existence is:

exists $hash{$key}