$re = '/(?<=CN\=).*?(?=,)/mi';
$str = 'Computer Location = afp.local/EANG
Description = RED_TXT
Device Name = EANG04W
Domain Name = afp.local
Full Name = Admintech
Hardware Monitoring Type = ASIC2
Last Blocked Application Scan Date = 1420558125
Last Custom Definition Scan Date = 1348087114
Last Hardware Scan Date = 1420533869
Last Policy Sync Date = 1420533623
Last Software Scan Date = 1420533924
Last Update Scan Date = 1420558125
Last Vulnerability Scan Date = 1420558125
LDAP Location = **CN=EANG04W**,OU=EANG,DC=afp,DC=local
Login Name = ADMINTECH
Main Board OEM Name = Dell Inc.
Number of Files = 384091
Primary Owner = **CN= LOUHICHI anoir**,OU=EANG,DC=afp,DC=localenter code here';
$subst = "Company";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
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 PHP, please visit: http://php.net/manual/en/ref.pcre.php