I do not know where it comes from. The script is a nagios check to monitor the updates.spamassassin.org channel:

#!/usr/bin/perl

use warnings;
use strict;
use Mail::SpamAssassin;
use Net::DNS;

# variables
my ( $sa_version, $rev_sa_version, $SA, $update_dir, $version_on_disk,
    $LOCAL_STATE_DIR, $resolver, $query, $version_dns, $sa_channel );

# get the SpamAssassin version from the Perl module
$sa_version =  Mail::SpamAssassin::Version();

# reverse this number. We will need it for a txt forware query later
$rev_sa_version = join(".", reverse split(/\./, $sa_version) ) ;

# sa channel we want to monitor
$sa_channel = "updates.spamassassin.org";

# get the local state dir update path
$LOCAL_STATE_DIR = '/var/lib/spamassassin';

$SA = Mail::SpamAssassin->new( {
        LOCAL_STATE_DIR => $LOCAL_STATE_DIR,
    }
);

$update_dir = $SA->sed_path('__local_state_dir__/__version__');

# inside $update_dir, get the line starting with "# UPDATE "
# save the version in $version_on_disk

if ( -e "$update_dir/updates_spamassassin_org.cf" ) {
    open (CF, "$update_dir/updates_spamassassin_org.cf" ) or die "$!\n
+";
    while (<CF> ) {
        last unless /^# UPDATE\s+[A-Za-z]+\s+(\S+)/;
        $version_on_disk = $1;
    }
}

print "$sa_channel channel version on disk is:  $version_on_disk\n";

$resolver = Net::DNS::Resolver->new;

$query = $resolver->query("$rev_sa_version.$sa_channel", 'txt');

if ( $query ) {
    for my $rr ( $query->answer ) {
        $version_dns = $rr->rdata;
    }
}

print "$sa_channel channel dns txt query version is $version_dns\n";

print "[$version_on_disk]\t version on disk\n";
print "[$version_dns]\t version dns\n";

if ( "$version_on_disk" >= "$version_dns" ) {
    print "OK: the $sa_channel version on disk is up to date: $version
+_on_disk\n";
    exit 0;
}
else {
    print "WARNING: there is a newer version available for SpamAssassi
+n $sa_channel rules (on disk version is $version_on_disk, new version
+ is $version_dns. Run sa-update -D as root to upgrade your SpamAssass
+in channel version.\n";
    exit 1;
}
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I added the [] chars around $version_on_disk and $version_dns to make sure no strange characters were coming on the variables. They print correctly on the terminal.

Specifically use Data::Dumper and $Data::Dumper::Useqq=1;(!!) to see control characters in strings

I added the [] chars around $version_on_disk and $version_dns to make sure no strange characters were coming on the variables. They print correctly on the terminal.

How can you detect a sound in brackets? Use Data::Dumper (plus $Data::Dumper::Useqq=1; as advised by jethro) or pipe your output to a hexdump.
Updated.

Can you show the content of the file "$update_dir/updates_spamassassin_org.cf" ?

Exactly! ^G1195874 is certainly not a number. Perl is loosely typed but it doesn't mean it should be used in strange ways, like expecting alpha-numeric characters to be treated like numbers.

You might like to re-consider the two (rather) 'strings' you're trying to compare!

I understand your point, but when I print it with [] around the variables, it prints without the leading ^G:

print "[$version_on_disk]\t version on disk\n";
print "[$version_dns]\t version dns\n";
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gives me:

[1195874]        version on disk
[1195874]        version dns
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So how does that ^G get in front of my variable :?

The other thing to realize is that a control-G is probably not a printable character. After all, it's supposed to ring a bell (on a teletype) or make some kind of beep noise (on a terminal).

Try piping your output through od.

Perhaps using regex:

#!/usr/bin/perl -w
use strict;

my $version_on_disk = "\aabfd\nadsf\n\n555";
my $version_dns ="lkjh\a\n\r\n\a89";

foreach ($version_on_disk, $version_dns)
{
   $_ =~ s/[^[:print:]]//g; #delete non-printable chars
}

print "$version_on_disk $version_dns\n";
#prints: abfdadsf555 lkjh89
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