my %column_num;
my @column_lbls = qw( Id Name SSN Phone FAX );
# initialize a hash with an array index:
@column_num{ @column_lbls } = 0 .. $#column_lbls;

# to find the index of the item matching $col_name:
my $index = $column_lbls{$col_name};

# to find the column numbers of several columns (e.g., a database query):
my @cols = @column_lbls{ qw(Name Phone FAX) };