G'day perlynewby,

You're sort of on the right track. Here's where I see problems:

• You only need one hash — see code examples below.
• Splitting on /\s*=\s/ won't work with "dieci =diez" because there's no whitespace after the '=': you just need to change that to /\s*=\s*/ (greedily matching zero or more whitespace characters either side of the '=').
• I suspect where you really got lost was with the foreach loop: probably due to using two hashes in the first place.
• In addition, just throwing random code at the problem is a big mistake. For instance, you don't use Storable and I see no reason to sort keys. While you're learning, adding code to see what it does can be very useful; just leaving it there afterwards becomes problematic.
• While I don't see that it's caused a problem here, I'd recommend giving a bit more thought to your naming conventions. You have $in1 associated with the data2 file, while $out1 is associated with the data_out1 file: variable 1, 2nd file, labelled 2 vs. variable 1, 2nd file, labelled 1.

Having pointed out places where there's problems, I will commend you on the IO: lexical filehandles; 3-argument open; checking return values; using $!. All good - well done! In the examples below, I've used Inline::Files. Read about it if you want. The only pertinent part is that I'm using a while loop with a filehandle: read it the same as your code, I'm just using a different filehandle.

"check if the number is found in both files."

Let's start with doing just that and nothing else.

#!/usr/bin/env perl -l

use strict;
use warnings;

use Inline::Files;

my %seen;

while (<ITES>) {
    ++$seen{(split)[0]};
}

while (<ITFR>) {
    my $key = (split)[0];
    print $key if $seen{$key};
}

__ITES__
uno = uno
due = dos
tre = tres
quattro = quatro
cinque = cinco
sei = seis
sette = siete
otto = ocho
nouve = nueve
dieci =diez
__ITFR__
uno = un
due = due
tre = tris
quattro = quatre
cinque = cinq
sei = six
sette = sept
dieci = dix
[download]

Output:

uno
due
tre
quattro
cinque
sei
sette
dieci
[download]

Now you have working code that does what you want. One hash; two while loops; no foreach required.

Let's build on that to get the output you're after.

#!/usr/bin/env perl -l

use strict;
use warnings;

use Inline::Files;

my %seen;

while (<ITES>) {
    chomp;
    my ($key, $val) = split /\s*=\s*/;
    $seen{$key} = $val;
}

while (<ITFR>) {
    chomp;
    my ($key, $val) = split /\s*=\s*/;
    print "$key => $seen{$key}, $val" if $seen{$key};
}

__ITES__
uno = uno
due = dos
tre = tres
quattro = quatro
cinque = cinco
sei = seis
sette = siete
otto = ocho
nouve = nueve
dieci =diez
__ITFR__
uno = un
due = due
tre = tris
quattro = quatre
cinque = cinq
sei = six
sette = sept
dieci = dix
[download]

Output:

uno => uno, un
due => dos, due
tre => tres, tris
quattro => quatro, quatre
cinque => cinco, cinq
sei => seis, six
sette => siete, sept
dieci => diez, dix
[download]

As you can see, the basic structure of the code hasn't changed. The first while loop is almost identical to yours (with the regex fixed).

The second while loop starts like yours. But then just uses the same print ... if $seen{$key}; from my first example; the only real difference is that, having captured more data, we now have more information to print.

To learn more about hashes in Perl, see "perldata - Perl data types" and "perldsc - Perl Data Structures Cookbook".

Lastly, you have spelling mistakes in your data. For instance, two and three in French are deux and trois. I'll leave you to check the rest.