Ignoring Things – Version Control with Git

Version Control with Git

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 data
$ touch a.png b.png c.png data/a.csv data/b.nc

and see what Git says:

$ git status

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

    a.png
    b.png
    c.png
    data/

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

*.png
data/

These patterns tell Git to ignore any file whose name ends in .png and everything in the data 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 forecast
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 png files and the data folder"
$ git status

On branch forecast
nothing to commit, working tree clean

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

$ git add a.png

The following paths are ignored by one of your .gitignore files:
a.png
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.csv. We can also always see the status of ignored files if we want:

$ git status --ignored

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

        a.png
        b.png
        c.png
        data/

nothing to commit, working tree clean

Ignoring Nested Files

Given a directory structure that looks like:

data/csv
data/plots

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

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

data/plots/

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

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 .png files in your root directory except for final.png? Hint: Find out what ! (the exclamation point operator) does

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

*.png           # ignore all png files
!final.png      # except final.png

The exclamation point operator will include a previously excluded entry.

Note if you’ve previously committed .png files they will not be ignored with this new rule. Only future additions of .png 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:

data/csv
data/images
data/plots
data/analysis

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

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

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

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

Ignoring all data Files in a Directory

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

data/csv/global/temperature/a.dat
data/csv/global/temperature/b.dat
data/csv/global/temperature/c.dat
data/csv/global/temperature/info.txt
data/plots

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

Solution (Solution). Appending data/csv/global/temperature/*.dat will match every file in data/csv/global/temperature that ends with .dat. The file data/csv/global/temperature/info.txt will not be ignored.

Ignoring all data Files in the repository

Let us assume you have many .csv files in different subdirectories of your repository. For example, you might have:

results/a.csv
data/experiment_1/b.csv
data/experiment_2/c.csv
data/experiment_2/variation_1/d.csv

How do you ignore all the .csv files, without explicitly listing the names of the corresponding folders?

Solution (Solution). In the .gitignore file, write:

**/*.csv

This will ignore all the .csv files, regardless of their position in the directory tree. You can still include some specific exception with the exclamation point operator.

The Order of Rules

Given a .gitignore file with the following contents:

*.csv
!*.csv

What will be the result?

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

Write one .gitignore entry that excludes files of the form log_01, log_02, etc.
Test your “ignore pattern” by creating some dummy files of the form log_01, etc.
You find that the file log_01 is very important after all, add it to the tracked files without changing the .gitignore again.
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 (Solution).

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

Keypoints

The .gitignore file tells Git what files to ignore.