use strict;
my $str = 'UPDATE pass
SET stato = -3, descr_stato = \'Scartata\' WHERE pratica = \'1458\'
AND stato = 0
AND anno IN (2016, 2017, 2018);
UPDATE pass
SET stato = -3, descr_stato = \'Scartata\'
WHERE pratica = \'2383\' AND stato = 0 AND anno IN (2020);';
my $regex = qr/SET(.*?)WHERE/msp;
my $subst = 'WHERE';
my $result = $str =~ s/$regex/$subst/rg;
print "The result of the substitution is' $result\n";
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for Perl, please visit: http://perldoc.perl.org/perlre.html