use strict;
my $str = 'a:ABC,b:SDSD,c:213123#a:SDS,b:UIOU,c:89797#a:TYRQQQW,b:UIOUIOYYO,c:546654 a:DFSS,b:TYRTTN,c:12323#a:HJH,b:YTUUUTYUTYT,c:67890 a:TYY,b:OPIUIU,c:86768';
my $regex = qr/[^b]:[^,]*,?/mp;
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