I'm sure that by now you've gotten a number of good answers, but I couldn't resist working with this one. What happens with the statement:

push @data, %tmp;
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Is that the hash is flattened into a list, and the hash structure is lost. Wrapping %tmp in curly brackets i.e. '{' and '}' turns %tmp into an anonymous hash and that preserves the hash structure.

push @data, { %tmp };

and later ..

print $data[0]->{COMPONENT};
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Code where you can see all this (play with the push statement) is given below:

#!/usr/bin/perl
use warnings;
use strict;
use Data::Dumper;

my $file = "<DATA>";
my @columns = ( "ONE", "TWO", "THREE", "FOUR", "FIVE" );

my @AoH = read_dat($file);
print Data::Dumper->Dump(\@AoH);

print "\n\nArray of hash element: ", $AoH[0]->{"THREE"}, "\n";


sub read_dat
{
    my $file = shift;
    my @data = ();
    
    for my $line( <DATA> ) {
        next unless $line =~ m/\w+/;
        my @line = split (",", $line);
        my $i = 0;
        my %tmp;
        
        foreach my $col (@columns){
            $tmp{$col} = $line[$i];
            $i++;
        }
        push @data, { %tmp };
    
    }
    return @data;
}
__DATA__
0,1,2,3,4
1,2,3,4,5
2,3,4,5,6
3,4,5,6,7
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Update: typo fixes

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