Question

If a key exists in a array, I want to print that key and its values from hash. Here is the code I wrote.

for($i=0;$i<@array.length;$i++)
{
    if (exists $hash{$array[$i]})
    {
        print OUTPUT $array[$i],"\n";
    }
}

From the above code, I am able to print keys. But I am not sure how to print values of that key.

Can someone help me?

Thanks

Answer 1

@array.length is syntactically legal, but it’s definitely not what you want.

@array, in scalar context, gives you the number of elements in the array.

The length function, with no argument, gives you the length of $_.

The . operator performs string concatenation.

So @array.length takes the number of elements in @array and the length of the string contained in $_, treats them as strings, and joins them together. $i < ... imposes a numeric context, so it’s likely to be treated as a number — but surely not the one you want. (If @array has 15 elements and $_ happens to be 7 characters long, the number should be 157, a meaningless value.)

The right way to compute the number of elements in @array is just @array in scalar context — or, to make it more explicit, scalar @array.

To answer your question, if $array[$i] is a key, the corresponding value is $hash{$array[$i]}.

But a C-style for loop is not the cleanest way to traverse an array, especially if you only need the value, not the index, on each iteration.

foreach my $elem (@array) {
    if (exists $hash{$elem}) {
        print OUTPUT "$elem\n";
    }
}