my @array1 = qw(a b c d e);
my @array2 = qw(a c d e b);

# assign numbers and create lookup table
my $i;
my %pos1 = map { $_ => ++$i } @array1;

# lookup items of array2
my @pos2 = map $pos1{$_}, @array2;

print "@pos2\n";  # 1 3 4 5 2