One regex expression using php

Question

I have a doubt related to a regular expression in php.

$content = "START FIRST AAA SECOND AAA"
$content_first = preg_replace('/START(.*)AAA/', 'REPLACED_STRING', $content);
//$content_first == "REPLACED_STRING"
$content_second = preg_replace('/START(.*?)AAA/', 'REPLACED_STRING', $content);
//$content_second == "REPLACED_STRING SECOND AAA"

Why exactly does $content_second differ from $content_first? What is the purpose of '?' in a regex? I have the following regex (really extensive) and I want to modify it so it replaces ALL urls in a string instead of stopping by the first one, but I'm not being able to (it just finds the first URL in the string):

$url_pattern = '/# Rev:20100913_0900 github.com\/jmrware\/LinkifyURL
    # Match http & ftp URL that is not already linkified.
      # Alternative 1: URL delimited by (parentheses).
      (\()                     # $1  "(" start delimiter.
      ((?:ht|f)tps?:\/\/[a-z0-9\-._~!$&\'()*+,;=:\/?#[\]@%]+)  # $2: URL.
      (\))                     # $3: ")" end delimiter.
    | # Alternative 2: URL delimited by [square brackets].
      (\[)                     # $4: "[" start delimiter.
      ((?:ht|f)tps?:\/\/[a-z0-9\-._~!$&\'()*+,;=:\/?#[\]@%]+)  # $5: URL.
      (\])                     # $6: "]" end delimiter.
    | # Alternative 3: URL delimited by {curly braces}.
      (\{)                     # $7: "{" start delimiter.
      ((?:ht|f)tps?:\/\/[a-z0-9\-._~!$&\'()*+,;=:\/?#[\]@%]+)  # $8: URL.
      (\})                     # $9: "}" end delimiter.
    | # Alternative 4: URL delimited by <angle brackets>.
      (<|&(?:lt|\#60|\#x3c);)  # $10: "<" start delimiter (or HTML entity).
      ((?:ht|f)tps?:\/\/[a-z0-9\-._~!$&\'()*+,;=:\/?#[\]@%]+)  # $11: URL.
      (>|&(?:gt|\#62|\#x3e);)  # $12: ">" end delimiter (or HTML entity).
    | # Alternative 5: URL not delimited by (), [], {} or <>.
      (                        # $13: Prefix proving URL not already linked.
        (?: ^                  # Can be a beginning of line or string, or
        | [^=\s\'"\]]          # a non-"=", non-quote, non-"]", followed by
        ) \s*[\'"]?            # optional whitespace and optional quote;
      | [^=\s]\s+              # or... a non-equals sign followed by whitespace.
      )                        # End $13. Non-prelinkified-proof prefix.
      ( \b                     # $14: Other non-delimited URL.
        (?:ht|f)tps?:\/\/      # Required literal http, https, ftp or ftps prefix.
        [a-z0-9\-._~!$\'()*+,;=:\/?#[\]@%]+ # All URI chars except "&" (normal*).
        (?:                    # Either on a "&" or at the end of URI.
          (?!                  # Allow a "&" char only if not start of an...
            &(?:gt|\#0*62|\#x0*3e);                  # HTML ">" entity, or
          | &(?:amp|apos|quot|\#0*3[49]|\#x0*2[27]); # a [&\'"] entity if
            [.!&\',:?;]?        # followed by optional punctuation then
            (?:[^a-z0-9\-._~!$&\'()*+,;=:\/?#[\]@%]|$)  # a non-URI char or EOS.
          ) &                  # If neg-assertion true, match "&" (special).
          [a-z0-9\-._~!$\'()*+,;=:\/?#[\]@%]* # More non-& URI chars (normal*).
        )*                     # Unroll-the-loop (special normal*)*.
        [a-z0-9\-_~$()*+=\/#[\]@%]  # Last char can\'t be [.!&\',;:?]
      )                        # End $14. Other non-delimited URL.
    /imx';

Can anyone help me out or head me towards the right direction? Thank you so much!

Ok, I think I understood all your explanations (ty for that!), is there any reason that only my first url is to be put between 'a' tags? rest of the code:

$url_replace = '$1$4$7$10$13<a>$2$5$8$11$14</a>$3$6$9$12';
return preg_replace($url_pattern, $url_replace, $text);

if

$text = 
http://www.youtube.com/watch?v=Cy8duEIHEig http://www.youtube.com/watch?v=Cy8duEIHEig

Only the first URL appears as an URL. Has this something to do with the *? ?

score 0 · Answer 1 · answered Feb 05 '14 at 14:53

0

? does two things. First it can make a expression optional for example

ab?c

where b is optional or second an in your case

.*?

it disables the greedy algorithm of .* -> It finds the first and smallest match.

answered Feb 05 '14 at 14:53

tea2code

1,007
1
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what exactly do you mean with smallest? – user111671 Feb 05 '14 at 14:54
It stops as soon as it finds whatever you have after the '?' – Joao Raposo Feb 05 '14 at 14:56
@JoaoRaposo could you check the answer update please? – user111671 Feb 05 '14 at 15:04
This bit of your regex seems to be causing problems: ( (?: ^ | [^=\s\'"\]] ) \s*[\'"]? | [^=\s]\s+ ) – Joao Raposo Feb 05 '14 at 15:22

score 0 · Answer 2 · edited May 23 '17 at 12:03

0

The difference between $content_first and $content_second is well explained here: What do lazy and greedy mean in the context of regular expressions?

$content_first is greedy, which means after matching START, it matches as many characters as possible, so the AAA suffix in the regex is actually omitted. $content_second causes PCRE to match any characters until it meets AAA.

edited May 23 '17 at 12:03

Community

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answered Feb 05 '14 at 14:55

Piotr

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One regex expression using php

2 Answers2