in reply to Match a string that can contain a carriage return in a random position.

This seems to deal with al the pathelogical break points I tried. 

#!perl -slw
use strict;

my @lines;
my $buffer;
while( <DATA> ){
    chomp;
    $buffer .= $_;                         #! Accumulate in buffer
    if ($buffer =~ /^(cn=.+?)cn=/) {    #! When we have a full line+
        push @lines, $1;                #! save it
        substr($buffer, 0, $+[1], '');  #! and strip from the buffer
    }
}
push@lines,$buffer;

print for @lines;

[download]

Test data

__DATA__
c
n=Perl Monks,ou=Bedchambers,ou=Monastery,c=Universe
cn
=Pe rl Monks,ou=Bedchambers,ou=Monastery,c=Universe
cn=
Perl Monks,ou=Bedchambers,ou=Monastery,c=Universe
cn=P
erl Monks,ou=Bedchambers,ou=Monastery,c=Universe
cn=Perl Monks,ou=Bedchambers,
ou=Monastery,c=Universe
cn=Per
l Monks,ou=Bedchambers,
ou=Monastery,c=Universe
cn=Perl Monks
,ou=Bedchambers,ou=Monas
tery,c=Universe
cn=Perl Monks,o
u=Bedchambers,ou=Monas
tery,c=Universe
cn=Perl Monks,ou=Bedc
hambers,ou=Monastery,c=Universe
cn=Perl Monks,ou=Bedchamber
s,ou=Monastery,c=Universe
cn=Perl Monks,ou=Bedchambers,ou=
Monastery,c=Universe
cn=Perl Monks,ou=Bedchambers,ou=Monastery,
c=Universe
cn=Perl Monks,ou=Bedchambers,ou=Monastery,c
=Universe
cn=Perl Monks,ou=Bedchambers,ou=Monastery,c=
Universe
cn=Perl Monks,ou=Bedchambers,ou=Monastery,c=U
niverse
cn=Perl Monks,ou=Bedchambers,ou=Monastery,c=Univers
e

[download]

Examine what is said, not who speaks.

In Section Seekers of Perl Wisdom