Thank you to all. I give my final solution, that seems to work as it could be useful for another one.

$main::Report="";
sub note {
    my ($titre,$texte) = @_;
    print STDERR "*update.pl(($titre,$texte)) \n";    
    my $Texte= '<H5>'.$titre.'</H5><P>'.$texte.'</P>';
    $main::Report .=$Texte;
    print STDERR "*update.pl:$Texte\n[\n$main::Report\n]\n";
}
...
note($title,$text);
...
print STDERR "*update.pl: end \n[\n$main::Report\n]\n";
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