Regex - PHP Lookaround

Question

I have a string, such as this:

$foo = 'Hello __("How are you") I am __("very good thank you")'

I know it's a strange string, but stay with me please :P

I need a regex expression that will look for the content between __("Look for content here") and put it in an array.

i.e. the regular expression would find "How are you" and "very good thank you".

__(?<=__$").*?(?="$)__ should work. – anomareh Mar 09 '10 at 19:12 — anomareh, Mar 09 '10 at 19:12

Bart Kiers · Accepted Answer · 2010-03-09T19:25:42.667

8

Try this:

preg_match_all('/(?<=__\(").*?(?="\))/s', $foo, $matches);
print_r($matches);

which means:

(?<=     # start positive look behind
  __\("  #   match the characters '__("'
)        # end positive look behind
.*?      # match any character and repeat it zero or more times, reluctantly
(?=      # start positive look ahead
  "\)    #   match the characters '")'
)        # end positive look ahead

EDIT

And as Greg mentioned: someone not too familiar with look-arounds, it might be more readable to leave them out. You then match everything: __(", the string and ") and wrap the regex that matches the string, .*?, inside parenthesis to capture only those characters. You will then need to get your matches though $matches[1]. A demo:

preg_match_all('/__\("(.*?)"\)/', $foo, $matches);
print_r($matches[1]);

edited Mar 09 '10 at 19:25

answered Mar 09 '10 at 19:15

Bart Kiers

166,582
36
299
288

1

Wouldn't it be simpler to use `/__$"(.*?)"$/` and then extract the matching group? I always find those lookbehind and lookahead matches hard to read. – Greg Hewgill Mar 09 '10 at 19:19
Why, thank you Jamie, nice to know there is at least one more person who thinks I am, besides my 2,5 year old son! :) – Bart Kiers Mar 09 '10 at 19:20
@Greg Hewgill, yes, that is also an option. Perhaps one preferable for Jamie. I'll edit shortly. – Bart Kiers Mar 09 '10 at 19:21
@anomareh, yes, I wrote a little tool myself that spits out such an explanation. – Bart Kiers Mar 09 '10 at 19:22
2

@Greg Hewgill: Yes, it will *absolutely* be simpler and better to use your regular expression. Because the first look-behind assertion will be tested for each position of the test string. I would also use a negated character class instead of a non-greedy universal character expression: `/__$"([^"]*)"$/`. – Gumbo Mar 09 '10 at 19:32
@bart Ah before you formatted it, it looked like a jumbled mess from some web app :p Neat tool. – anomareh Mar 09 '10 at 19:52

score 2 · Answer 2 · answered Mar 09 '10 at 19:50

If you want to use Gumbo's suggestion, credit goes to him for the pattern:

$foo = 'Hello __("How are you")I am __("very good thank you")';

preg_match_all('/__\("([^"]*)"\)/', $foo, $matches);

Make sure to use $matches[1] for your results unless you want the full string results too.

var_dump() of $matches:

array
  0 => 
    array
      0 => string '__("How are you")' (length=16)
      1 => string '__("very good thank you")' (length=25)
  1 => 
    array
      0 => string 'How are you' (length=10)
      1 => string 'very good thank you' (length=19)

Regex - PHP Lookaround

2 Answers2

Linked