Ignoring Things

Overview

Teaching: 5 min
Exercises: 0 min

Questions

• How can I tell Git to ignore files I don’t want to track?

Objectives

• Configure Git to ignore specific files.

• Explain why ignoring files can be useful.

What if we have files that we do not want Git to track for us, like backup files created by our editor or intermediate files created during data analysis? Let’s create a few dummy files:

$ mkdir results
$ touch a.dat b.dat c.dat results/a.out results/b.out

and see what Git says:

$ git status

On branch master
Untracked files:
  (use "git add <file>..." to include in what will be committed)

	a.dat
	b.dat
	c.dat
	results/

nothing added to commit but untracked files present (use "git add" to track)

Putting these files under version control would be a waste of disk space. What’s worse, having them all listed could distract us from changes that actually matter, so let’s tell Git to ignore them.

We do this by creating a file in the root directory of our project called .gitignore:

$ nano .gitignore
$ cat .gitignore

*.dat
results/

These patterns tell Git to ignore any file whose name ends in .dat and everything in the results directory. (If any of these files were already being tracked, Git would continue to track them.)

Once we have created this file, the output of git status is much cleaner:

$ git status

On branch master
Untracked files:
  (use "git add <file>..." to include in what will be committed)

	.gitignore

nothing added to commit but untracked files present (use "git add" to track)

The only thing Git notices now is the newly-created .gitignore file. You might think we wouldn’t want to track it, but everyone we’re sharing our repository with will probably want to ignore the same things that we’re ignoring. Let’s add and commit .gitignore:

$ git add .gitignore
$ git commit -m "Ignore data files and the results folder."
$ git status

# On branch master
nothing to commit, working directory clean

As a bonus, using .gitignore helps us avoid accidentally adding to the repository files that we don’t want to track:

$ git add a.dat

The following paths are ignored by one of your .gitignore files:
a.dat
Use -f if you really want to add them.

If we really want to override our ignore settings, we can use git add -f to force Git to add something. For example, git add -f a.dat. We can also always see the status of ignored files if we want:

$ git status --ignored

On branch master
Ignored files:
 (use "git add -f <file>..." to include in what will be committed)

        a.dat
        b.dat
        c.dat
        results/

nothing to commit, working directory clean

Ignoring Nested Files

Given a directory structure that looks like:

results/data
results/plots

How would you ignore only results/plots and not results/data?

Solution

If you only want to ignore the contents of results/plots, you can change your .gitignore to ignore only the /plots/ subfolder by adding the following line to your .gitignore:

results/plots/

This line will ensure only the contents of results/plots is ignored, and not the contents of results/data.

As with most programming issues, there are a few alternative ways that one may ensure this ignore rule is followed. The “Ignoring Nested Files: Variation” exercise has a slightly different directory structure that presents an alternative solution. Further, the discussion page has more detail on ignore rules.

Including Specific Files

How would you ignore all .dat files in your root directory except for final.dat? Hint: Find out what ! (the exclamation point operator) does

Solution

You would add the following two lines to your .gitignore:

*.dat           # ignore all data files
!final.dat      # except final.data

The exclamation point operator will include a previously excluded entry.

Note also that because you’ve previously committed .dat files in this lesson they will not be ignored with this new rule. Only future additions of .dat files added to the root directory will be ignored.

Ignoring Nested Files: Variation

Given a directory structure that looks similar to the earlier Nested Files exercise, but with a slightly different directory structure:

results/data
results/images
results/plots
results/analysis

How would you ignore all of the contents in the results folder, but not results/data?

Hint: think a bit about how you created an exception with the ! operator before.

Solution

If you want to ignore the contents of results/ but not those of results/data/, you can change your .gitignore to ignore the contents of results folder, but create an exception for the contents of the results/data subfolder. Your .gitignore would look like this:

results/*               # ignore everything in results folder
!results/data/          # do not ignore results/data/ contents

Ignoring all data Files in a Directory

Assuming you have an empty .gitignore file, and given a directory structure that looks like:

results/data/position/gps/a.dat
results/data/position/gps/b.dat
results/data/position/gps/c.dat
results/data/position/gps/info.txt
results/plots

What’s the shortest .gitignore rule you could write to ignore all .dat files in result/data/position/gps? Do not ignore the info.txt.

Solution

Appending results/data/position/gps/*.dat will match every file in results/data/position/gps that ends with .dat. The file results/data/position/gps/info.txt will not be ignored.

The Order of Rules

Given a .gitignore file with the following contents:

*.dat
!*.dat

What will be the result?

Solution

The ! modifier will negate an entry from a previously defined ignore pattern. Because the !*.dat entry negates all of the previous .dat files in the .gitignore, none of them will be ignored, and all .dat files will be tracked.

Log Files

You wrote a script that creates many intermediate log-files of the form log_01, log_02, log_03, etc. You want to keep them but you do not want to track them through git.

1. Write one .gitignore entry that excludes files of the form log_01, log_02, etc.

2. Test your “ignore pattern” by creating some dummy files of the form log_01, etc.

3. You find that the file log_01 is very important after all, add it to the tracked files without changing the .gitignore again.

4. Discuss with your neighbor what other types of files could reside in your directory that you do not want to track and thus would exclude via .gitignore.

Solution

1. append either log_* or log* as a new entry in your .gitignore
2. track log_01 using git add -f log_01

Key Points

• The .gitignore file tells Git what files to ignore.