hgignore: help ignoring all files but certain ones

The answer from Michael is a fine one, but another option is to just exclude:

foo/bar/**

and then manually add the .jar files. You can always add files that are excluded by an ignore rule and it overrides the ignore. You just have to remember to add any jars you create in the future.

Anyone that wants to use negative lookaheads (or ?! in regex syntax) or any kind of back-referencing mechanism should be aware that Mercurial will fall back from google's RE2 to Python's re module for matching.

RE2 is a non-backtracking engine that guarantees a run-time linear with the size of the input. If performance is important to you, that is if you have a big repository, you should consider sticking to more simple patterns that Re2 supports, which is why I think that the solution offered by Ryan.

To do this, you'll need to use this regular expression:

foo/bar/.+?\.(?!jar).+

Explanation

You are telling it what to ignore, so this expression is searching for things you don't want.

1. You look for any file whose name (including relative directory) includes (foo/bar/)
2. You then look for any characters that precede a period ( .+?\. == match one or more characters of any time until you reach the period character)
3. You then make sure it doesn't have the "jar" ending (?!jar) (This is called a negative look ahead
4. Finally you grab the ending it does have (.+)

Regular expressions are easy to mess up, so I strongly suggest that you get a tool like Regex Buddy to help you build them. It will break down a regex into plain English which really helps.

EDIT

Hey Jason S, you caught me, it does miss those files.

This corrected regex will work for every example you listed:

foo/bar/(?!.*\.jar$).+

It finds:

• foo/bar/baz.txt
• foo/bar/baz
• foo/bar/jar
• foo/bar/baz.jar.txt
• foo/bar/baz.jar.
• foo/bar/baz.
• foo/bar/baz.txt.

But does not find

• foo/bar/baz.jar

New Explanation

This says look for files in "foo/bar/" , then do not match if there are zero or more characters followed by ".jar" and then no more characters ($ means end of the line), then, if that isn't the case, match any following characters.