$re = '/^(.+)(?<!\\\\)((?:\\\\\\\\)*)(\!\=|(?<!\!|\<|\>)=|\<\=|\>\=)(.+)$/m';
$str = 'name=toto
tat\\=a
bla\\bla=tor
blood\\\\=orange
wrong\\\\\\=cops
right\\\\\\\\=escaping
extrem\\\\\\\\\\=slash
hoho\\\\\\\\\\\\=ho
is\\\\\\\\\\\\\\=magic
noend=
dou=bl=equal
ma\\=tche!=operation
is\\\\!=not
is<=inferior
is>=superior
tha>t=isno<t
-----
^(.+)((?<!\\\\)=)(.+)$';
$subst = "[$1$2] $3 [$4]";
$result = preg_replace($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