Replace, But Only Include Delimiters in Certain Cases

Question

In PHP, I need to replace a fixed prefix and suffix surrounding a variable value.

The quotes around the value are stripped, except if the value is a string.

[blargh="5"]                  =>   <potato chips=#5#>
[blargh="97"]                 =>   <potato chips=#97#>
[blargh="StackOverflow"]      =>   <potato chips=#"StackOverflow"#>

I know that somehow, I can use preg_replace() to do this, but I do not know how.

Answer 1

Branch Reset: (?| ... )

The tricky part in your question is that for "StackOverflow" we include the quotes in the replacement, but for "87" we strip them. No fear, the branch reset feature handles that gracefully.

In the Regex Demo , see the substitutions at the bottom.

Sample PHP Code

$yourstring = '[blargh="5"] [blargh="97"] [blargh="StackOverflow"]';
$replaced = preg_replace('~\[blargh=(?|"(\d+)"|("[^"]*"))\]~',
                          '<potato chips=#\1#>', 
                          $yourstring);
echo $replaced;

Output

<potato chips=#5#> <potato chips=#97#> <potato chips=#"StackOverflow"#>

Our Search Regex:

\[blargh=(?|"(\d+)"|("[^"]*"))\]

Our Replacement String

<potato chips=#\1#>

Explanation

• \\[blargh= matches literal chars
• In the branch reset (?| .... ) , the groups all capture to Group 1
• "(\\d+)" captures digits inside quotes to Group 1 (but don't capture the quotes)
• OR |
• ("[^"]*") capture a complete "quoted string" to Group 1
• \\] matches the closing bracket
• In the replacement, <potato chips=#\\1#> , \\1 is a back-reference to Group 1

Reference

• Branch Reset
• perlre doc

Answer 2

You can use regular expression using a callback as well.

$text = '[blargh="5"] would convert, [blargh="97"] and [blargh="StackOverflow"]';

$text = preg_replace_callback('~\[blargh="([^"]*)"\]~', 
      function($m) {
         $which = is_numeric($m[1]) ? $m[1] : '"'.$m[1].'"';
         return '<potato chips=#' . $which . '#>';
      }, $text);

echo $text;

Output

<potato chips=#5#> would convert, <potato chips=#97#> and <potato chips=#"StackOverflow"#>