Select substring “_id” in string using regular expressions

Question

I need help with regular expressions. I need to select "_id" and replace it with "_ID", but don't know how to do it exactly right. Example string: "test_id" must be as "test_ID", but "test_identification_number" must not be "test_IDentification_number".

Currently I have such regex: /(?:_id$| id )/, but it won't work, because it cannot replace _id with _ID and _id_ with _ID_ .

Thanks.

**Edit: I use PHP for it.

Answer 1

I'd use this pattern:

preg_replace('/(?<=_)id(\b|_)/', 'ID$1', $string);

demo

How it works:

• (?<=_) : positive lookbehind: The rest of the pattern will only match if it's preceded by an underscore. The underscore itself is not captured (ie not replaced)
• id : String literal -> matches id , obviously
• (\\b|_) : grouping match for either a word-boundary ( \\b ), or an underscore. This grouping is required, because a positive lookahead like (?:\\b|_) will capture the trailing underscore (so you'd have to replace it with 'ID$1' , but that will fail if the lookahead matches a word boundary ( see regex101 )

Answer 2

You can use the word boundary qualifier : \\b will only match at the start of the string, the end of the string or if the previous or following character isn't a word character.

so _id\\b should only match words ending in _id , and not _identifier .

Answer 3

My solution

Search string: /(?<=_)id\\b/g

Replace string: ID

Answer 4

使用preg_replace基于正则表达式进行替换。

$string_modified = preg_replace('/_id(\b|_)/','_ID$1',$string);