use strict;
my $str = 'Field 1 : Data
Field 2 : data
Some other data: Data
Some more data = fubar
And yet more information = stuff
And here is more : http://data
Custom input=
Hi there, this is custom input. It may be many paragraphs long, but, it is always until the end of the email itself.';
my $regex = qr/(?s)(.+)(Custom input=.+)/mp;
my $subst = '\\2';
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