CODEWITHSUNDEEP
regex
neuquen
neuquen

Reputation: 4169

Match Everything Except a Variable String

I have been able to match all text within a string that looks like the below:

[!--$element--]

using the below regex:

\[!--(.*?)]

However, now I want to match everything EXCEPT the above string, but can't seem to get it to work. I've attempted to use the not ^ expression and the look-ahead ?! expression, but can't seem to get it right.

For example,

I want 

This is an [!--$element--]

to turn into:

[!--$element--]

I am using PHPs preg_replace() to remove all text that isn't an [--$element--]

Any idea how I can do so?

Upvotes: 2

Views: 239

Answers (4)

zx81
zx81

Reputation: 41838

Capture Group, (*SKIP)(*F) or Split

To match this, we have several options.

Option 1: With capture groups

This is a longer way to do it, but it will work in all engines.

\[!--[^-]*--\]|((?:(?!\[!--[^-]*--\]).)+)

The strings you want are in Group 1. In the Regex Demo, look at the captures in the right panel.

Option 2: (*SKIP)(*F)

This will only work in Perl and PCRE (and therefore PHP). It matches the strings directly.

\[!--[^-]*--\](*SKIP)(*F)|(?:(?!\[!--[^-]*--\]).)+

In the Regex Demo, see the matched strings.

Option 3: Split

Match All and Split are Two Sides of the Same Coin, so we can use preg_split instead of preg_match_all. By splitting the string, we remove the pieces we want to exclude.

$element_regex = '~\[!--[^-]*--\]~';
$theText = preg_split($element_regex, $yourstring);

Explanation

This problem is a classic case of the technique explained in this question to "regex-match a pattern, excluding..."

Option 1. In Option 1, The left side of the alternation | matches complete [!--$element--]. We will ignore these matches. The right side matches and captures other text, and we know it is the right ones because it was not matched by the expression on the left.

Option 2. In Option 2, the left side of the alternation | matches complete [!--$element--] then deliberately fails, after which the engine skips to the next position in the string. The right side matches the this word you want, and we know they are the right ones because they were not matched by the expression on the left.

Reference

Upvotes: 3

Jan Moritz
Jan Moritz

Reputation: 2215

Note that I didn't used [!--(.*?)] because it will also match elements that are different from [!--$element--] like [!--$element]

<?php
$text ='This is an [!--$element--]. Here is some other text';
preg_match_all('#(\[\!--.*--\])#',$text,$out);
print_r($out);
?>

And the output is

Array
(
    [0] => Array
        (
            [0] => [!--$element--]
        )

    [1] => Array
        (
            [0] => [!--$element--]
        )

)

Here is the online Demo

Upvotes: 0

Zombiesplat
Zombiesplat

Reputation: 953

use preg_replace with this pattern Demo

preg_replace("/(.*)(\[!--.*?])(.?)/", "\1\3", $input_lines);

Upvotes: 0

Ry-
Ry-

Reputation: 224904

Instead of replacing the text you don’t want, just grab the text you do want:

preg_match_all('/\[!--(.*?)]/', $input, $matches);
$result = implode('', $matches[0]);

Demo

Upvotes: 2

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