use strict;
use warnings;

my @array1 = (1,2,3);
my @array2 = (1,2,3,4,5);
my %hash;

@hash{@array1} = @array1;

my @only2 = grep {! exists $hash{$_}} @array2;

# remove the unwanted "value"
@array1 = grep {$_ != 2} @array1;
@array2 = grep {$_ != 2} @array2;

push @array1, shift @only2;

print "array 1:\n";
print "$_\n" for @array1;

print "array 2:\n";
print "$_\n" for @array2;