I'm trying to replace text which is between underscores with the tag. This is what pattern I'm currently using (Link to online tester: TESTER):
[^\\]?_(([^_]*)[^\\])_
This is the result I want to get:
_test1_ _test2__test3_ \_test4\_ => <b>test1</b> <b>test2</b><b>test3</b> \_test4\_
Can anyone tell me whats wrong with my pattern?
You may use
(?<!\\)((?:\\{2})*)_([^_\\]*(?:\\.[^_\\]*)*)_
PHP declaration:
$pattern = '~(?<!\\\\)((?:\\\\{2})*)_([^_\\\\]*(?:\\\\.[^_\\\\]*)*)_~';
See the regex demo
Details:
(?<!\\)((?:\\{2})*)_ - matches an unescaped _: any number of double \ symbols (see (?:\\{2})*, 0+ sequences of two consecutive \ symbols) that are not preceded with a \ ((?<!\\) negative lookbehind performs this check)([^_\\]*(?:\\.[^_\\]*)*)_ - matches any number of symbols other than _ or any number of escaped symbols thus only matching up to the first unescaped _.[^_\\]* - matches 0+ chars other than \ and _(?:\\.[^_\\]*)* - 0+ sequences of:\\. - any escaped char (if you use s DOTALL modifier, even a line break char)[^_\\]* - 0+ chars other than \ and _To use the same approach in JavaScript and other regex engines that do not support a lookbehind, use (^|[^\\]) group instead of (?<!\\):
(^|[^\\])((?:\\{2})*)_([^_\\]*(?:\\.[^_\\]*)*)_
And replace with $1$2<b>$3</b>. See this regex demo.