Version Control with Git

Ignoring Things

Learning 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 "Add the ignore file"
$ 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.
fatal: no files added

If we really want to override our ignore settings, we can use git add -f to force Git to add something. 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?

Including specific files

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

Ignoring files deep in a directory

Given a directory structure that looks like:

results/data/position/gps/useless.data
results/plots

What’s the shortest .gitignore rule you could write to ignore all .data files in result/data/position/gps Hint: What does appending ** to a rule accomplish?

The order of rules

Given a .gitignore file with the following contents:

*.data
!*.data

What will be the result?

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.