Re: parsing print_r() output with preg_match_all()

From	Thomas 'PointedEars' Lahn <PointedEars@web.de>
Newsgroups	comp.lang.php
Subject	Re: parsing print_r() output with preg_match_all()
Date	2016-01-07 11:17 +0100
Organization	PointedEars Software (PES)
Message-ID	<1918095.oM0jGXUH9t@PointedEars.de> (permalink)
References	<568d3dcf$0$23748$e4fe514c@news.xs4all.nl>

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R.Wieser wrote:
^^
Please post here using your first name, too.

> I'm saving the contents of an array-of-arrays into a string with
> print_r(). Now I want to parse the contents of that string into an
> array-of-arrays again.

You should not do that.

> I've found some code which is supposed to do that (at
> http://nl3.php.net/print_r), but it seems to depend on TAB chars being
> present in the output -- and those do not appear in mine.
> 
> So, I tried to alter the used regexp to the preg_match_all() function,
> which is where all the fun started: I cannot seem to find a notation which
> will just add the detection of a closing bracket (ending a sub-array).
> 
> Can anyone here lend me a hand ?
> 
> The offending line :
> 
> if (preg_match_all('/^\s+\[(\w+).*\] => (.*)\n/m', $printr, $match)) {

In computer linguistics, the branch of computer science dealing with formal 
languages, the formal grammar that can produce the output of print_r() in 
this case is context-free (Chomsky type-2), and the languages that can be 
produced by such a grammar are context-free languages.

Therefore, it is in general not possible to parse such languages with one 
application of one *regular* expression, because *regular* expressions are a 
tool to describe *regular* languages (Chomsky type-3); IOW, a regular 
expression will in general either match too much when greedy (default) or 
too little when non-greedy.  The relation is thus: All regular languages are 
context-free, but not all context-free languages are regular. 

The nested, paired parentheses in the print_r() output show that the 
print_r() output language cannot be regular: the language of well-
formed/balanced parentheses/brackets (bracket language) is the textbook 
example of a context-free language that is not regular, which can be shown 
by application of the pumping lemma for regular languages.

PHP supports Perl-Compatible Regular Expressions which provide the “(?R…)” 
feature to match text recursively.  This makes it possible to match nested 
balanced parentheses to a certain degree (as far as stack memory permits).

However, to be on the safe side you would need to write a parser for this 
language (which would basically be an implementation of a deterministic 
push-down automaton, but can use regular expressions; but depending on the 
programming language that is not necessarily the most efficient approach – 
in PHP, where regular expressions are not objects, it probably is not).

But it is easier to use existing parsers for other formats.  For example, 
since you say in <news:568d6f9c$0$23759$e4fe514c@news.xs4all.nl> that you 
need human-readable output (which excludes the built-in serialization 
mechanism to binary), you should look into JSON which PHP supports with an 
extension.  Other alternatives that come to mind are CSON, YAML, and XML (in 
that order, with increasing overhead).  PHP also has built-in XML support, 
and there is a PECL extension for YAML (not bundled with PHP).

<https://en.wikipedia.org/wiki/Chomsky_hierarchy>
<http://php.net/manual/en/regexp.reference.recursive.php>
<http://php.net/json>
<http://php.net/xml>
<http://php.net/yaml>

-- 
PointedEars
Zend Certified PHP Engineer
Twitter: @PointedEars2
Please do not cc me. / Bitte keine Kopien per E-Mail.

Thread

parsing print_r() output with preg_match_all()  "R.Wieser" <address@not.available> - 2016-01-06 17:18 +0100
  Re: parsing print_r() output with preg_match_all() Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-01-06 19:28 +0000
    Re: parsing print_r() output with preg_match_all() "R.Wieser" <address@not.available> - 2016-01-06 20:50 +0100
      Re: parsing print_r() output with preg_match_all() Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-01-06 21:12 +0000
        Re: parsing print_r() output with preg_match_all() Jerry Stuckle <jstucklex@attglobal.net> - 2016-01-06 16:20 -0500
          Re: parsing print_r() output with preg_match_all() Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-01-07 02:23 +0000
            Re: parsing print_r() output with preg_match_all() Matthew Carter <m@ahungry.com> - 2016-01-06 21:48 -0500
              Re: parsing print_r() output with preg_match_all() Matthew Carter <m@ahungry.com> - 2016-01-06 21:52 -0500
                Re: parsing print_r() output with preg_match_all() "R.Wieser" <address@not.available> - 2016-01-07 10:20 +0100
                Re: parsing print_r() output with preg_match_all() Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-01-07 10:56 +0000
                Re: parsing print_r() output with preg_match_all() Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-01-07 12:55 +0100
                Re: parsing print_r() output with preg_match_all() Jerry Stuckle <jstucklex@attglobal.net> - 2016-01-07 08:36 -0500
                Re: parsing print_r() output with preg_match_all() Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-01-07 13:58 +0000
                Re: parsing print_r() output with preg_match_all() Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-01-07 15:33 +0100
                Re: parsing print_r() output with preg_match_all() Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-01-07 15:31 +0000
                Re: parsing print_r() output with preg_match_all() Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-01-07 18:23 +0100
            Re: parsing print_r() output with preg_match_all() Jerry Stuckle <jstucklex@attglobal.net> - 2016-01-06 22:50 -0500
            Re: parsing print_r() output with preg_match_all() "R.Wieser" <address@not.available> - 2016-01-07 10:10 +0100
          Re: parsing print_r() output with preg_match_all() "R.Wieser" <address@not.available> - 2016-01-07 10:03 +0100
            Re: parsing print_r() output with preg_match_all() Jerry Stuckle <jstucklex@attglobal.net> - 2016-01-07 08:38 -0500
              Re: parsing print_r() output with preg_match_all() Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-01-07 14:05 +0000
                Re: parsing print_r() output with preg_match_all() Jerry Stuckle <jstucklex@attglobal.net> - 2016-01-07 13:42 -0500
                Re: parsing print_r() output with preg_match_all() Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-01-07 20:24 +0000
                Re: parsing print_r() output with preg_match_all() Jerry Stuckle <jstucklex@attglobal.net> - 2016-01-07 15:27 -0500
        Re: parsing print_r() output with preg_match_all() "R.Wieser" <address@not.available> - 2016-01-07 09:51 +0100
          Re: parsing print_r() output with preg_match_all() Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-01-07 11:18 +0000
            Re: parsing print_r() output with preg_match_all() "R.Wieser" <address@not.available> - 2016-01-07 14:00 +0100
              Re: parsing print_r() output with preg_match_all() Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-01-07 14:00 +0000
              Re: parsing print_r() output with preg_match_all() "R.Wieser" <address@not.available> - 2016-01-07 16:19 +0100
      Re: parsing print_r() output with preg_match_all() Arno Welzel <usenet@arnowelzel.de> - 2016-01-11 09:11 +0100
        Re: parsing print_r() output with preg_match_all() Jerry Stuckle <jstucklex@attglobal.net> - 2016-01-11 08:04 -0500
          Re: parsing print_r() output with preg_match_all() Arno Welzel <usenet@arnowelzel.de> - 2016-01-11 23:48 +0100
            Re: parsing print_r() output with preg_match_all() Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-01-12 00:41 +0100
              Re: parsing print_r() output with preg_match_all() Jerry Stuckle <jstucklex@attglobal.net> - 2016-01-11 20:53 -0500
                Re: parsing print_r() output with preg_match_all() Arno Welzel <usenet@arnowelzel.de> - 2016-01-12 05:40 +0100
                Re: parsing print_r() output with preg_match_all() Jerry Stuckle <jstucklex@attglobal.net> - 2016-01-12 09:12 -0500
                Re: parsing print_r() output with preg_match_all() Arno Welzel <usenet@arnowelzel.de> - 2016-01-12 21:43 +0100
                Re: parsing print_r() output with preg_match_all() Jerry Stuckle <jstucklex@attglobal.net> - 2016-01-12 16:12 -0500
                Re: parsing print_r() output with preg_match_all() Arno Welzel <usenet@arnowelzel.de> - 2016-01-12 22:28 +0100
                Re: parsing print_r() output with preg_match_all() Jerry Stuckle <jstucklex@attglobal.net> - 2016-01-12 16:35 -0500
                Re: parsing print_r() output with preg_match_all() Arno Welzel <usenet@arnowelzel.de> - 2016-01-13 06:39 +0100
                Re: parsing print_r() output with preg_match_all() Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-01-13 08:26 +0100
                Re: parsing print_r() output with preg_match_all() Jerry Stuckle <jstucklex@attglobal.net> - 2016-01-13 08:10 -0500
                Re: parsing print_r() output with preg_match_all() Arno Welzel <usenet@arnowelzel.de> - 2016-01-13 14:49 +0100
                Re: parsing print_r() output with preg_match_all() Jerry Stuckle <jstucklex@attglobal.net> - 2016-01-13 10:08 -0500
                Re: parsing print_r() output with preg_match_all() Arno Welzel <usenet@arnowelzel.de> - 2016-01-13 18:50 +0100
                Re: parsing print_r() output with preg_match_all() Jerry Stuckle <jstucklex@attglobal.net> - 2016-01-13 15:06 -0500
                Re: parsing print_r() output with preg_match_all() Arno Welzel <usenet@arnowelzel.de> - 2016-01-13 23:11 +0100
                Re: parsing print_r() output with preg_match_all() Jerry Stuckle <jstucklex@attglobal.net> - 2016-01-13 17:18 -0500
                Re: parsing print_r() output with preg_match_all() Arno Welzel <usenet@arnowelzel.de> - 2016-01-13 23:27 +0100
                Re: parsing print_r() output with preg_match_all() Jerry Stuckle <jstucklex@attglobal.net> - 2016-01-13 19:17 -0500
                Re: parsing print_r() output with preg_match_all() Arno Welzel <usenet@arnowelzel.de> - 2016-01-14 01:30 +0100
                Re: parsing print_r() output with preg_match_all() Jerry Stuckle <jstucklex@attglobal.net> - 2016-01-13 20:52 -0500
                Re: parsing print_r() output with preg_match_all() Arno Welzel <usenet@arnowelzel.de> - 2016-01-14 08:13 +0100
                Re: parsing print_r() output with preg_match_all() Jerry Stuckle <jstucklex@attglobal.net> - 2016-01-14 09:18 -0500
                Re: parsing print_r() output with preg_match_all() Arno Welzel <usenet@arnowelzel.de> - 2016-01-14 20:07 +0100
                Re: parsing print_r() output with preg_match_all() Jerry Stuckle <jstucklex@attglobal.net> - 2016-01-14 16:06 -0500
                Re: parsing print_r() output with preg_match_all() Arno Welzel <usenet@arnowelzel.de> - 2016-01-14 22:41 +0100
                Re: parsing print_r() output with preg_match_all() Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-01-14 22:35 +0100
                Re: parsing print_r() output with preg_match_all() Ian Collins <ian-news@hotmail.com> - 2016-01-14 10:24 +1300
                Re: parsing print_r() output with preg_match_all() Jerry Stuckle <jstucklex@attglobal.net> - 2016-01-13 17:20 -0500
                Re: parsing print_r() output with preg_match_all() Ian Collins <ian-news@hotmail.com> - 2016-01-14 12:14 +1300
                Re: parsing print_r() output with preg_match_all() Jerry Stuckle <jstucklex@attglobal.net> - 2016-01-13 19:18 -0500
                Re: parsing print_r() output with preg_match_all() Arno Welzel <usenet@arnowelzel.de> - 2016-01-14 08:34 +0100
                Re: parsing print_r() output with preg_match_all() Anders Wegge Keller <wegge@geostat.dk> - 2016-01-14 09:20 +0100
                Re: parsing print_r() output with preg_match_all() Ian Collins <ian-news@hotmail.com> - 2016-01-14 21:56 +1300
                Re: parsing print_r() output with preg_match_all() Jerry Stuckle <jstucklex@attglobal.net> - 2016-01-14 16:08 -0500
                Re: parsing print_r() output with preg_match_all() Arno Welzel <usenet@arnowelzel.de> - 2016-01-14 22:55 +0100
                Re: parsing print_r() output with preg_match_all() Jerry Stuckle <jstucklex@attglobal.net> - 2016-01-14 16:59 -0500
                Re: parsing print_r() output with preg_match_all() Arno Welzel <usenet@arnowelzel.de> - 2016-01-14 23:09 +0100
                Re: parsing print_r() output with preg_match_all() Ian Collins <ian-news@hotmail.com> - 2016-01-15 11:17 +1300
                Re: parsing print_r() output with preg_match_all() Jerry Stuckle <jstucklex@attglobal.net> - 2016-01-14 19:15 -0500
                Re: parsing print_r() output with preg_match_all() Jerry Stuckle <jstucklex@attglobal.net> - 2016-01-14 19:14 -0500
            Re: parsing print_r() output with preg_match_all() Jerry Stuckle <jstucklex@attglobal.net> - 2016-01-11 20:50 -0500
              Re: parsing print_r() output with preg_match_all() Arno Welzel <usenet@arnowelzel.de> - 2016-01-12 05:42 +0100
                Re: parsing print_r() output with preg_match_all() Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-01-12 08:41 +0100
                Re: parsing print_r() output with preg_match_all() Jerry Stuckle <jstucklex@attglobal.net> - 2016-01-12 09:13 -0500
                Re: parsing print_r() output with preg_match_all() Arno Welzel <usenet@arnowelzel.de> - 2016-01-12 21:44 +0100
                Re: parsing print_r() output with preg_match_all() Jerry Stuckle <jstucklex@attglobal.net> - 2016-01-12 16:13 -0500
                Re: parsing print_r() output with preg_match_all() Arno Welzel <usenet@arnowelzel.de> - 2016-01-12 22:29 +0100
                Re: parsing print_r() output with preg_match_all() Jerry Stuckle <jstucklex@attglobal.net> - 2016-01-12 16:33 -0500
        Re: parsing print_r() output with preg_match_all() Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-01-12 00:49 +0100
          Re: parsing print_r() output with preg_match_all() Jerry Stuckle <jstucklex@attglobal.net> - 2016-01-11 20:54 -0500
  Re: parsing print_r() output with preg_match_all() Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-01-07 11:17 +0100
    Re: parsing print_r() output with preg_match_all() "R.Wieser" <address@not.available> - 2016-01-07 13:49 +0100
      Re: parsing print_r() output with preg_match_all() Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-01-07 14:20 +0100
        Re: parsing print_r() output with preg_match_all() "R.Wieser" <address@not.available> - 2016-01-07 15:31 +0100
          Re: parsing print_r() output with preg_match_all() Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-01-07 16:00 +0100
          Re: parsing print_r() output with preg_match_all() Jerry Stuckle <jstucklex@attglobal.net> - 2016-01-07 13:45 -0500
            Re: parsing print_r() output with preg_match_all() "R.Wieser" <address@not.available> - 2016-01-07 20:18 +0100
              Re: parsing print_r() output with preg_match_all() Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-01-07 20:52 +0100
                Re: parsing print_r() output with preg_match_all() Jerry Stuckle <jstucklex@attglobal.net> - 2016-01-07 15:29 -0500
            Re: parsing print_r() output with preg_match_all() Tim Streater <timstreater@greenbee.net> - 2016-01-07 22:42 +0000
              Re: parsing print_r() output with preg_match_all() "R.Wieser" <address@not.available> - 2016-01-08 10:43 +0100
  Re: parsing print_r() output with preg_match_all() Arno Welzel <usenet@arnowelzel.de> - 2016-01-11 09:07 +0100
    Re: parsing print_r() output with preg_match_all() Jerry Stuckle <jstucklex@attglobal.net> - 2016-01-11 08:05 -0500
      Re: parsing print_r() output with preg_match_all() Arno Welzel <usenet@arnowelzel.de> - 2016-01-11 23:51 +0100
        Re: parsing print_r() output with preg_match_all() Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-01-12 00:31 +0100
        Re: parsing print_r() output with preg_match_all() Jerry Stuckle <jstucklex@attglobal.net> - 2016-01-11 20:55 -0500
        Re: parsing print_r() output with preg_match_all() "R.Wieser" <address@not.available> - 2016-01-12 11:11 +0100
          Re: parsing print_r() output with preg_match_all() - question remains unanswered ... "R.Wieser" <address@not.available> - 2016-01-12 11:54 +0100
            Re: parsing print_r() output with preg_match_all() - question remains unanswered ... Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-01-12 11:25 +0000
              Re: parsing print_r() output with preg_match_all() - question remains unanswered ... "R.Wieser" <address@not.available> - 2016-01-12 13:41 +0100
                Re: parsing print_r() output with preg_match_all() - question remains unanswered ... "Christoph M. Becker" <cmbecker69@arcor.de> - 2016-01-12 14:11 +0100
                Re: parsing print_r() output with preg_match_all() - question remainsunanswered ... "R.Wieser" <address@not.available> - 2016-01-12 14:34 +0100
                Re: parsing print_r() output with preg_match_all() - question remainsunanswered ... "Christoph M. Becker" <cmbecker69@arcor.de> - 2016-01-12 15:03 +0100
                Re: parsing print_r() output with preg_match_all() - questionremainsunanswered ... "R.Wieser" <address@not.available> - 2016-01-12 15:50 +0100
                Re: parsing print_r() output with preg_match_all() - questionremainsunanswered ... "Christoph M. Becker" <cmbecker69@arcor.de> - 2016-01-12 16:36 +0100
                Re: parsing print_r() output with preg_match_all() - Solved. "R.Wieser" <address@not.available> - 2016-01-12 21:28 +0100
                Re: parsing print_r() output with preg_match_all() - question remains unanswered ... Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-01-12 14:02 +0000
            Re: parsing print_r() output with preg_match_all() - question remains unanswered ... "Christoph M. Becker" <cmbecker69@arcor.de> - 2016-01-12 12:42 +0100
              Re: parsing print_r() output with preg_match_all() - question remainsunanswered ... "R.Wieser" <address@not.available> - 2016-01-12 14:20 +0100
            Re: parsing print_r() output with preg_match_all() - question remains unanswered ... Jerry Stuckle <jstucklex@attglobal.net> - 2016-01-12 09:43 -0500
              Re: parsing print_r() output with preg_match_all() - question remainsunanswered ... "R.Wieser" <address@not.available> - 2016-01-12 16:11 +0100

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