Ignoring Files and Reading History

.gitignore

Some files should never be committed: logs, build output, editor backup files, downloaded dependencies, and above all secrets like passwords and keys. List patterns for them in a file named .gitignore at the top of the repository, and commit it, so the rules travel with the project ^{1 2}.

# logs and editor leftovers
*.log
*~
*.swp

# build output, in any folder
build/

# only the notes.txt at the top level
/notes.txt

# local secrets, but keep the example file
.env
!.env.example

The rules ²:

• # starts a comment; blank lines are ignored.
• Wildcards work as in the shell: *.log, secret*.txt, photo?.jpg.
• A pattern ending in / matches only directories: build/.
• A pattern with a / at the start or middle is relative to the folder the .gitignore is in: /notes.txt means only the top-level one, docs/draft.md only that path. Without a slash, it matches at any depth.
• ** matches across folders: logs/**/*.txt.
• A leading ! makes an exception, re-including something an earlier pattern excluded.

Untracked files that match no longer show up in git status, and git add . skips them.

Ignore rules don’t affect files git already tracks ¹. If you committed something you shouldn’t have, stop tracking it while keeping it on disk, then commit:

me@linuxbox:~/garden$ git rm --cached debug.log
me@linuxbox:~/garden$ git commit -m "Stop tracking debug.log"

If what you committed was a password or key, removing it doesn’t help: it’s still in history, and in every copy of the repository. Change the password or replace the key.

To see which rule ignores a file:

me@linuxbox:~/garden$ git check-ignore -v build/out.txt
.gitignore:7:build/ build/out.txt

Patterns for your machine and habits, in every repository, like your editor’s backup files, go in ~/.config/git/ignore, which git reads by default ².

Reading history

git log has many options; these are the ones worth knowing ¹:

me@linuxbox:~/garden$ git log --oneline --graph       # compact; shows branches (module 3)
me@linuxbox:~/garden$ git log -p -2                   # the last two commits, with their changes
me@linuxbox:~/garden$ git log --stat                  # which files each commit touched
me@linuxbox:~/garden$ git log -- beds.txt             # only commits that changed beds.txt

--stat gives a quick summary:

me@linuxbox:~/garden$ git log --stat -1
commit 11bf5331f9afdf0c3eb7804dfbb149dc46d7e4a3
Author: Me <me@example.com>
Date:   Mon Oct 5 11:10:00 2026 -0500

    Add lettuce

 beds.txt | 1 +
 1 file changed, 1 insertion(+)

The -- before a path tells git that what follows is a file name, not a branch or option ¹.

Searching history

• git log -S word finds commits whose changes added or removed that text; Pro Git calls it the “pickaxe” ¹.
• git log --grep=word searches commit messages.
• --since=2.weeks, --until=2026-09-01, and --author=name narrow by date and person ¹.

me@linuxbox:~/garden$ git log -S fence --oneline
3d80cdb Plan the fence

One commit, one line

git show displays a single commit, its message and its changes. Name commits by ID, or relative to where you are: HEAD is the current commit, HEAD~1 the one before it, HEAD~3 three back ¹.

me@linuxbox:~/garden$ git show --stat --oneline HEAD~1
3ce82ab Describe the beds in the README
 README.md | 2 ++
 1 file changed, 2 insertions(+)

git blame shows, for each line of a file, which commit last changed it, who, and when ¹:

me@linuxbox:~/garden$ git blame beds.txt
^adc6083 (Me 2026-10-05 09:00:00 -0500 1) tomatoes
^adc6083 (Me 2026-10-05 09:00:00 -0500 2) beans
82d8b55c (Me 2026-10-05 09:20:00 -0500 3) carrots
c2ee0569 (Me 2026-10-05 10:00:00 -0500 4) peas
11bf5331 (Me 2026-10-05 11:10:00 -0500 5) lettuce

The ^ marks lines from the very first commit. Then git show 82d8b55c tells you why that line was added, which is where good commit messages pay off.

Your turn

So

.gitignore keeps logs, build output, and secrets out of the repository, with wildcards, trailing / for folders, leading / for top-level paths, and ! for exceptions; it doesn’t affect files already tracked, so use git rm --cached for those. git log with --oneline, -p, --stat, a path, -S, and --grep answers most history questions, and git show and git blame zoom in.