Question 42330 in PHP Question posted in
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regex non-fixed-width lookaround – PHP

I am trying to match curly quotes that are inside shortcodes and replace them with normal quotes but leave the ones outside.

Here is an example content:

“foobar” [tagname id=“1035” linked=“true”] “another” [tagname id=“1”]

Should output the following:

“foobar” [tagname id="1035" linked="true"] “another” [tagname id="1"]

It can be PCRE or Javascript regex. Any suggestions is appreciated.

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2

Answers


  1. 0

    Since this is a little tricky, I am contributing from my end.

    So, we can,

    • match strings that follow a format of =“some_chars”

    • Since you have an additional constraint of match only if they are inside the square brackets, we will use positive lookahead ?= to match the above only if it is followed by a closing square bracket (since the string is uniformly formed, there will always be an opening square bracket which we won’t bother about).

    Snippet:

    <?php

$str = "outside=“bar” “foobar” [tagname id=“1035” linked=“true”] “another” [tagname id=“1”]";

echo preg_replace('/(=“([^”]*)”)(?=[^[]*])/', '="${2}"', $str);

    Online Demo

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  2. 0

    For doing replacements on substrings that match some pattern it’s often more efficient and comfortable to use a callback if available. With PHP and preg_replace_callback e.g.:

    $res = preg_replace_callback('~[[^][]*]~', function($m) {
  return str_replace(['“','”'], '"', $m[0]);
}, $str);

    This pattern matches an opening square bracket followed by any amount of characters that are no square brackets, followed by a closing square bracket. The callback function replaces quotes.

    Here is a PHP demo at tio.run. This can easily be translated to JS with replace function (demo).

    let res = str.replace(/[[^][]*]/g, m => { return m.replace(/[“”]/g,'"'); });

    Without callback in PCRE/PHP also the G anchor can be used to continue where the previous match ended. To chain matches to an opening square bracket (without checking for a closing).

    $res = preg_replace('~(?:G(?!^)|[)[^“”][]*K[“”]~u', '"', $str);

    See this demo at regex101 or another PHP demo at tio.run

    (?!^) prevents G from matching at start (default). K resets beginning of the reported match.

    To have it mentioned, another method could be to use a lookahead at each “ ” for checking if there is a closing ] ahead without any other square brackets in between: [“”](?=[^][]*])
    This does not check for an opening [ and works in all regex flavors that support lookaheads.

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