• Create a hash containing your mapping.
• Look up the source number and replace with the value from the hash as you process the input.
• Profit!

"Profit!"

Yeah; I hope OP will apply the result to my $cash!

use strict;
use warnings;

my %lookup = (
    1 => 567898,
    2 => 543267,
);

my @test = qw(0 a 2 1);
for (@test) {
    print exists $lookup{$_} ? $lookup{$_} : $_, "\n";
}

__END__
0
a
543267
567898
[download]

In the TMTOWTDI spirit, if your keys are really going to be "1", "2", "3", "4", and so on, you can use an array:

my @lookup;
@lookup[1..4] = (
    567898,
    543267,
    234565,
    987654,
);

my @test = qw(0 a 2 1);
for (@test) {
    print defined $lookup[$_] ? $lookup[$_] : $_, "\n";
}
[download]

This also looks like it could be a beginning programming assignment. Please show what you have done so far, and if it is homework, identify it as such.

Monks are not against helping you with a homework problem, they are just against doing your homework for you.

What I see resembles the basis for a simple substitution cipher, which is not a very secure form of encryption. If securing data cryptographically is what you're trying to do you may find that asking about encryption techniques or modules that implement them might be more fruitful.

#!/usr/bin/perl
use warnings;
use strict;

#
# hashes are superb for translations
#

my %translate = (
    1 => 567898,
    2 => 543267,
    3 => 234565,
    4 => 987654
);

my @data = ( 1, 2, 3, 4 );

for my $data (@data) {
    print $data, " => ", $translate{$data}, "\n";
}
[download]

C:\Code>perl translate.pl
1 => 567898
2 => 543267
3 => 234565
4 => 987654
[download]