I have this


and I am trying to use the vi regex command

% s/os\.environ\.get\("DB_NAME"\)/db_name/gc

to match that. I used it to change flaskdb to os.environ.get("DB_NAME"), but this won't match to change it to db_name.

On further investigation I was able to match it by removing the parenthesis.

How come I was able to escape the parenthesis to match the first change but not the second set of changes?

1 Answer 1


Vi uses Ex patterns, which are a superset of POSIX Basic (obsolete, according to man re_format) REs. This means that \( and \) are used for grouping, not to represent literal parentheses (as in "modern", or Extended, REs).

You can also find this information in Vim at :help pattern, which explains that with the default magic settings ( is literal and \( opens a group. With \v very-magic, this is reversed to make grouping easier (among other changes).

So, I would write


to change the entire os.environ.get("DB_NAME") expression, or


to only affect the DB_NAME.

With Vim, I might use a pattern like os\.environ\.get("\zsDB_NAME\ze") to match DB_NAME within os.environ.get(""), and I might use a replacement like \L& to lowercase the match (change DB_NAME to db_name).

An alternate idea is to /DB_NAME, or press * if you are already on the word, then gugn to lowercase the match. Then . jumps to the next match and lowercases, while n only jumps to the next match (so you can skip and act by combining n and .).

  • Excellent very informative Jul 12, 2022 at 6:36

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