my $header_row= 'one two three four five';
...
my %name2Index;
...
my $col=0;   
foreach my $col_head (split ' ',$header_row)
{
   $name2Index{$col_head} = $col++;
}

##</code><code>##

my @header_row = qw/ one two three four five /;
...
my %name2Index;
...
@name2Index{ @header_row } = 0 .. $#header_row;