How to tell git to ignore individual lines, i.e. gitignore for specific lines of code [duplicate]

Question

.gitignore can ignore whole files, but is there a way to ignore specific lines of code while coding?

I frequently and repeatedly add the same debug lines in a project, only to have to remember to remove them before committing. I'd like to just keep the lines in the code and have git disregard them.

Yiyid

I can't tell whether this is a terrible idea or a brilliant one. – Giesser

@KyleStrand at the very least, I can add it to debug lines I type and feel safe in knowing they won't be accidentally committed – Yiyid

Right, that's the "brilliant" part. – Giesser

Maybe I'd feel more comfortable with it if it could only be applied to print lines, or something. And I suppose that if there's a unit testing infrastructure in place that runs after each commit, this would be pretty safe. – Giesser

Oh, then you could just change the sed regex – Yiyid

@Miguelos Ha, it looks like it is a duplicate. Although the question is much older, the bounty-winning answer to that question is newer than my question and my answer here. – Yiyid

@KyleStrand I have now code in front of me that changes the first line of a properties file with a date each time a project is saved. For this scenario, it would be brilliant. If writing a date line is good practice, that's an whole other matter though :) – Osteoclasis

@Osteoclasis I would say that any time you find this feature useful on a recurring basis, it's probably a "config" smell. For instance, at my work we currently have a C# solution with a project that needs to be reconfigured to use the release version of a particular C++ dependency in order to run, even in debug mode, but the C++ project is part of the same MSVS solution, so there doesn't seem to be a clean way to do this without specifying the path to the compiled DLL and removing the dependency on the project. But we can't check that change in because it's not correct for deployment. – Giesser

Answer 1

This is how you can kind of do it with git filters:

1. Create/Open gitattributes file:
   • <project root>/.gitattributes (will be committed into repo)
     OR
   • <project root>/.git/info/attributes (won't be committed into repo)
2. Add a line defining the files to be filtered:
   • *.rb filter=gitignore, i.e. run filter named gitignore on all *.rb files
3. Define the gitignore filter in your gitconfig:
   • $ git config --global filter.gitignore.clean "sed '/#gitignore$/d'", i.e. delete these lines
   • $ git config --global filter.gitignore.smudge cat, i.e. do nothing when pulling file from repo

Notes:
Of course, this is for ruby files, applied when a line ends with #gitignore, applied globally in ~/.gitconfig. Modify this however you need for your purposes.

Warning!!
This leaves your working file different from the repo (of course). Any checking out or rebasing will mean these lines will be lost! This trick may seem useless since these lines are repeatedly lost on check out, rebase, or pull, but I've a specific use case in order to make use of it.

Just git stash save "proj1-debug" while the filter is inactive (just temporarily disable it in gitconfig or something). This way, my debug code can always be git stash apply'd to my code at any time without fear of these lines ever being accidentally committed.

I have a possible idea for dealing with these problems, but I'll try implementing it some other time.

Thanks to Rudi and jw013 for mentioning git filters and gitattributes.

Yiyid

Shouldn't that be: git config --global filter.gitignore.clean sed '/#gitignore$/d' since you've named the filter gitignore – Pyuria

Ah, indeed. In fact, there's also a quotation escaping issue. – Yiyid

Can I make it so that it replaces that line with something else? Like lets say I wanted to replace lines ending in #gitignore with "Here's a line of content" – Hydrocele

I did this for '.py'-files and ut worked. Then I did it again for '.xml'-files. That didn't work, and it also broke the previously working filter for python-files. Now I get this error all the time "error: external filter sed". Do you know how I can fix this or simply delete all filters? – Inveigle

Hm, I never tried doing this with more than one filetype at once, nor with nesting-format files like XML. In any case: 1 - Remove the lines you added in .gitattributes or .git/info/attributes that define which filter to use on what type of files. 2 - Open your .gitconfig and delete the lines where the clean and smudge commands are that filter. – Yiyid

Great answer! Maybe one could have the smudge filter check whether the already present old file would have ignored lines cleaned out and in that case prompt (to stderr) to mention either the removed lines or if somehow possible even manually do the stash applyish thing... – Lita

Where are the line numbers to ignore being specified ? – Counseloratlaw

This is interesting. But it basically acts like the line in question isn't there. It won't work for something like simply making the changes to a line be ignored. So you can't, for example, change the value of a variable in a function call. Eg, instead of changing flags = foo | bar to flags = foo | bar | debug_thingy, you'd have to make sure you add a completely new line like flags |= debug_thingy after. – Basrhin

So a open question remains: How to make it to work on line changes instead of only to line additions? – Luscious

I found a solution that works for me. I'm using git config --global filter.gitignore.clean "sed 's/.*gitignore//'" and replacing code like this , var x = replaced #gitignore var x = 42. So the content after the #gitignore replaces the line, so the indentation must be kept after the #gitignore. – Luscious

Here's also a sed command to ignore blocks of code "sed '/^# start git-block-ignore/,/^# end git-block-ignore/d;'" – Luscious

I used this feature and it worked. Later I started having issues with revert, restore, reset, and reset --hard. The problem was solved after deleting .git/info/attributes Is there any cleaner way to do this? – Cockfight

Not a complete solution for my use case, because it does not preserve local changes when checking out branches. I.e. I want specific local lines preserved while the rest of the file may be updated from the index, and then not committed. This may warrant a separate SO question. – Ethelred

Answer 2

I had a similar issue writing java code. My solution was to markup code that I didn't want to commit and then add a pre-commit hook that would look for my markup:

#!/bin/bash
#
# This hook will look for code comments marked '//no-commit'
#    - case-insensitive
#    - dash is optional
#    - there may be a space after the //
#
noCommitCount=$(git diff --no-ext-diff --cached | egrep -i --count "(@No|\/\/\s?no[ -]?)commit")
if [ "$noCommitCount" -ne "0" ]; then
   echo "WARNING: You are attempting to commit changes which include a 'no-commit'."
   echo "Please check the following files:"
   git diff --no-ext-diff --cached --name-only -i -G"(@no|\/\/s?no-?)commit" | sed 's/^/   - /'
   echo
   echo "You can ignore this warning by running the commit command with '--no-verify'"
   exit 1
fi

Put this into .git/hooks/pre-commit and give it a chmod +x .git/hooks/pre-commit

Usurer

Markup definitely feels less scary solution and declarative, than sed based filtering or such. Nice one. – Shortridge

git-scm.com/docs/githooks#_pre_commit – Unamerican

I would up vote this 100x if I could. This is a safe and straight forward sollution. Thank you! – Guyot