$re = '/^(?:\t| )*(?:#|%|;|//|--|REM|C|!) (?:#{64} (.*)|#{32} (.*)|#{16} (.*)|#{8} (.*)|#{4} (.*)|#{2} (.*))$/m';
$str = 'Valid comments that start with "#":
# ################################################################ First Level
# ################################ Second Level
# ################ Third level
# ######## Fourth Level
# #### Fifth level
# ## Sixth level
Valid comments that start with different characters:
// ################################################################ 1st Level
; ################################ 2nd Level
REM ################ 3rd level
C ######## 4th Level
% #### 5th level
-- ## 6th level
Valid comments that start with spaces or tabs:
# ################################################################ 1st level
; ################################ 2nd Level
Invalid comments:
################################################################ No initial character
; ################################################ Hashes not a power of 2
@ ################ Character not recognized
C ########No space after hashes
% %%%%%%%% No hashes
. # #### Period before spaces
;#### No space after character';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
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