use strict;
my $str = 'VIR RECU 998721687978
DE: Mrs PAUL SMITH
564';
my $regex = qr/^VIR\s+RECU\s+(\d+)\nDE:\s+([\s\S]*?)(\nMOTIF:\s+(.*))?$/p;
my $subst = '';
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