use strict;
my $str = 'PRELEVEMENT EUROPEEN 2001427553 DE: MUTUELLE DE L\'INDUSTRIE DU PETROLE ID: FR69MIP108863 MOTIF: Prelevement 42CXK 024 de MIP du 01/
VIR RECU 0485970259S DE: CPAM VAR MOTIF: 180930001235180930001235 REF: 18093000123';
my $regex = qr/.*(?: DE: (.*))(?: ID: (.*)){0,1}(?: MOTIF: (.*))(?: REF: (.*)){0,1}/mp;
my $subst = 'Tiers:\\t$1 \\rid:\\t$2 \\rmotif:\\t$3\\r\\r';
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