Regular expression in php with preg_match_all

Question

I would like to create a way of matching strings like

abc(xyz)
abc
abc(xyz)[123]

where each bracket is an optional unit. What I would like to have, optimally, is something like

preg_match_all('complicated regex', $mystring, $matches);

with $matches returning the following:

• If $mystring= abc(xyz)[123]R gives $matches=array(0 => "abc", 1=> "xyz", 2=> "123", 3=> "R")
• If $mystring= abc(xyz)R gives $matches=array(0 => "abc", 1=> "xyz", 2=> "", 3=> "R")
• If $mystring= abc[123]R gives $matches=array(0 => "abc", 1=> "", 2=> "123", 3=> "R")
• If $mystring= abc(xyz)[123] gives $matches=array(0 => "abc", 1=> "xyz", 2=> "123", 3=> "")
• If $mystring= abc gives $matches=array(0 => "abc", 1=> "", 2=> "", 3=> "")

I hope you get the point. I tried as follows:

preg_match_all("/([a-z]*)(\([a-zA-Z]\))?(\[\w\])?/", "foo(dd)[sdfgh]", $matches)

for which matches[0] is

Array
(
    [0] => foo
    [1] => 
    [2] => dd
    [3] => 
    [4] => 
    [5] => sdfgh
    [6] => 
    [7] => 
)

why do I get the additional empty matches? How to avoid them to have results as I need to (either in matches or in matches[0]...).

Answer 1

how about:

/^(\w*)(?:\((\w*)\))?(?:\[(\w*)\])(\w*)?$/

usage:

preg_match_all("/^(\w*)(?:\((\w*)\))?(?:\[(\w*)\])(\w*)?$/", "abc[123]R", $matches); 
print_r($matches);

output:

Array
(
    [0] => Array
        (
            [0] => abc[123]R
        )

    [1] => Array
        (
            [0] => abc
        )

    [2] => Array
        (
            [0] => 
        )

    [3] => Array
        (
            [0] => 123
        )

    [4] => Array
        (
            [0] => R
        )

)

explanation:

The regular expression:

(?-imsx:^(\w*)(?:\((\w*)\))?(?:\[(\w*)\])(\w*)?$)

matches as follows:

NODE                     EXPLANATION
----------------------------------------------------------------------
(?-imsx:                 group, but do not capture (case-sensitive)
                         (with ^ and $ matching normally) (with . not
                         matching \n) (matching whitespace and #
                         normally):
----------------------------------------------------------------------
  ^                        the beginning of the string
----------------------------------------------------------------------
  (                        group and capture to \1:
----------------------------------------------------------------------
    \w*                      word characters (a-z, A-Z, 0-9, _) (0 or
                             more times (matching the most amount
                             possible))
----------------------------------------------------------------------
  )                        end of \1
----------------------------------------------------------------------
  (?:                      group, but do not capture (optional
                           (matching the most amount possible)):
----------------------------------------------------------------------
    \(                       '('
----------------------------------------------------------------------
    (                        group and capture to \2:
----------------------------------------------------------------------
      \w*                      word characters (a-z, A-Z, 0-9, _) (0
                               or more times (matching the most
                               amount possible))
----------------------------------------------------------------------
    )                        end of \2
----------------------------------------------------------------------
    \)                       ')'
----------------------------------------------------------------------
  )?                       end of grouping
----------------------------------------------------------------------
  (?:                      group, but do not capture:
----------------------------------------------------------------------
    \[                       '['
----------------------------------------------------------------------
    (                        group and capture to \3:
----------------------------------------------------------------------
      \w*                      word characters (a-z, A-Z, 0-9, _) (0
                               or more times (matching the most
                               amount possible))
----------------------------------------------------------------------
    )                        end of \3
----------------------------------------------------------------------
    \]                       ']'
----------------------------------------------------------------------
  )                        end of grouping
----------------------------------------------------------------------
  (                        group and capture to \4 (optional
                           (matching the most amount possible)):
----------------------------------------------------------------------
    \w*                      word characters (a-z, A-Z, 0-9, _) (0 or
                             more times (matching the most amount
                             possible))
----------------------------------------------------------------------
  )?                       end of \4 (NOTE: because you are using a
                           quantifier on this capture, only the LAST
                           repetition of the captured pattern will be
                           stored in \4)
----------------------------------------------------------------------
  $                        before an optional \n, and the end of the
                           string
----------------------------------------------------------------------
)                        end of grouping
----------------------------------------------------------------------

Answer 2

You get so many results because your match starts on and on again 8 times. All The string (including empty strings) are matched against the first, non-optinal part of the regex: ([a-z]*).

The corrected regex:

preg_match_all("/^([a-z]*)(\([a-zA-Z]*\))?(\[\w*\])?$/", "foo(ddd)[sdfgh]", $matches); 

EDIT (to exclude brackets in the second part of the subject) So we want 'ddd' instead of '(ddd)':

This regex uses a "non capturing pattern" (?: ... ) in order to mark an optional part of the subject, but not to capture it in the matches array.

preg_match_all("/^([a-z]*)(?:\(([a-zA-Z]*)\))?(\[\w*\])?$/", "foo(ddd)[sdfgh]", $matches);

The interesting part is this: (?:\(([a-zA-Z]*)\))?.

• first paren (?: marks the beginning of a non capturing subpattern
• second paren \( is an escaped literal paren
• third one ( mark the beginning of standard capturing subpattern

Only contents of the third parens pair will show up in the $matches array.