git-update-index: add page

[yukuku]

• The page (if new), does not already exist in the repo.
• The page is in the correct platform directory (common/, linux/, etc.)
• The page has 8 or fewer examples.
• The PR title conforms to the recommended templates.
• The page follows the content guidelines.
• The page description includes a link to documentation or a homepage (if applicable).

[CLAassistant]

All committers have signed the CLA.

[tldr-bot]

The build for this PR failed with the following error(s):

pages/common/git-update-index.md:6: TLDR005 Example descriptions should end in a colon

Please fix the error(s) and push again.

[sbrl]

Thanks, @yukuku!

I'm curious about the use-case for this though. Very weird example!

[yukuku]

I've used this several times when dealing with repositories that I don't regularly maintain but has .gitignore that does not exclude temporary/build files that are produced on my machine.

e.g.

1. A repository does not exclude the out/ directory but when I build the project, the intermediate files are stored by default in out/ directory. I'm not familiar enough with this project so I don't want to add out/ to .gitignore an push that.

2. A repository has an instruction to patch certain lines in order for a hack to work, or in order to enable debug mode, or to increase network connection time out. The change modifies the source code but only for local developer's machine, it is not supposed to be commited.

[einverne]

hi @yukuku thank you for your contribution. I left a comment for you to take a look. It is ok with me after the change.

[sbrl]

Wow, that's such a very cool use-case @yukuku - thanks so much! I'll remember that one - it would have made a number of situations much easier :D

[waldyrious]

Hey @yukuku and @sbrl — just thought I'd mention that for the use case of a missing .gitignore in a project, you can easily set a repo-specific gitignore file by editing the .git/info/exclude file within the repo. That's more flexible than manually updating the index. Check the official docs and this StackOverflow Q&A for more info.