use Number::Format;
my $x = new Number::Format(-thousands_sep => ' ');
my $number = 1234567890;
print $x->format_number($number);
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$ perl example.pl
1 234 567 890
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You will need to install Number::Format from CPAN (see other answer)

You can also try this, but it does not take into account numbers with comma's:

my $number = 1234567890;
print format_number($number);

sub format_number{
    my($x) = @_;
    $x = reverse $x;
    $x =~ s/(\d{3})/$1 /g;
    $x = reverse $x;
    return $x;
}
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This prints:

1 234 567 890
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hello @FBRM Many Thanks for your reply! The better expression is "Mask" I have find also this: http://bip.weizmann.ac.il/course/prog2/pm/Number_Format.html "From germany"

#!/usr/bin/perl

$number = '12586'
use Number::Format qw(:subs :vars);
  $THOUSANDS_SEP   = '.';
  $DECIMAL_POINT   = ',';
  $INT_CURR_SYMBOL = 'DEM';
  my $formatted = format_number($number);
  
  
format_picture($number, '## ### ### ###')
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Gestion: How can i run this little stuff?

Greats,

@r