Making Changes
git log
Shows a history of commits, including author, date, and commit message.
git log --oneline
Sample output:
* 7f71eade (HEAD -> main) Adding fresh data for the survey.
* 1182c282 Added CSV data file
* 36b761e4 Added reminder to cite funding sources.
* e39ecc89 Added summary report file.
To find which commit caused an issue, note the first 6-8 characters of the commit hash, then use git show to inspect it:
git show 36b761e4
To look at the git history of a particular file:
git log sample-report.md
Customize Log Output
To look at the git history of a particular file:
git log sample-report.md
To limit the number of commits displayed:
git log -3 # limit to 3 commits
Restrict log by date:
git log --since='Month Day Year'
As an example:
-
Commits since 27 May 2019:
git log --since='May 27 2019' -
Commits between April 19 to June 30 2019:
git log --since='April 19 2019' --until='June 30 2019
git diff
This command shows changes in your files compared to previous commits or between specific commits. It works with both Git-tracked and untracked files.
git diff
Common ways to use git diff:
-
Compare working directory with the last commit:
git diff <file-path>Example:
git diff report.mdSample output:
diff --git a/report.md b/report.md
index e69de29..d95f3ad 100644
--- a/report.md
+++ b/report.md
@@ -1,3 +1,5 @@
+Reminder: Cite funding sources.
Data analysis results:
- Survey responses processed. -
Compare working directory with a specific commit:
git diff <commit-id> <file-path>Example:
git diff 123456 report.mdSample output:
diff --git a/report.md b/report.md
index d95f3ad..f3a1b2c 100644
--- a/report.md
+++ b/report.md
@@ -2,3 +2,4 @@
- Survey responses processed.
+Add final review comments. -
Compare two commits for a specific file:
git diff <commit-id-1> <commit-id-2> <file-path>Example:
git diff 123456 abcdef report.mdSample output:
diff --git a/report.md b/report.md
index e69de29..f3a1b2c 100644
--- a/report.md
+++ b/report.md
@@ -1,3 +1,5 @@
+Reminder: Cite funding sources.
Data analysis results:
- Survey responses processed.
+Add final review comments. -
Compare two files in the working directory or on disk:
git diff <file-path-1> <file-path-2>Example:
git diff report_v1.md report_v2.mdSample output:
diff --git a/report_v1.md b/report_v2.md
index e69de29..f3a1b2c 100644
--- a/report_v1.md
+++ b/report_v2.md
@@ -1,2 +1,3 @@
-Data analysis results:
+Data analysis results:
+Add final review comments. -
Compare the working directory with the latest commit for all files:
git diff -r HEADSample output:
diff --git a/report.md b/report.md
index e69de29..d95f3ad 100644
--- a/report.md
+++ b/report.md
@@ -1,3 +1,5 @@
+Reminder: Cite funding sources.
Data analysis results:
- Survey responses processed.
.diff File
A .diff file shows the differences between two versions of a file. It uses special symbols to indicate changes, which can be read by other systems to apply updates. Developers often use .diff files as patches to submit changes. Because all changes are in a single file, it’s called a unified diff.
Symbols in a unified diff:
| Symbol | Meaning |
|---|---|
+ | Line has been added |
- | Line has been removed |
/dev/null | Indicates a file has been added or removed |
(blank) | Context lines around changes |
@@ | Marks the start of a new block of changes |
index | Shows the commits being compared |
Here’s a sample unified diff for a file named check-network.yml:
diff --git a/check-network.yml b/check-network.yml
index 09b4f0c..b1978ca 100644
--- a/check-network.yml
+++ b/check-network.yml
@@ -4,7 +4,7 @@
roles:
- ansible-pyats
vars:
- snapshot_file: "{{ inventory_hostname }}_bgp.json"
+ snapshot_file: "{{ inventory_hostname }}_routes.json"
tasks:
- set_fact:
snapshot_data: "{{ lookup('file', snapshot_file) | from_json }}"
@@ -13,7 +13,7 @@
# var: snapshot_data
#
- pyats_parse_command:
- command: show ip route bgp
+ command: show ip route
compare: "{{ snapshot_data }}"
register: command_output
In this example:
- The line with
-shows the old code - The line with
+shows the new code - Context lines around changes indicates where the modification occurs
One change in this patch is renaming the snapshot file from ..._bgp.json to ..._routes.json.
- snapshot_file: "{{ inventory_hostname }}_bgp.json"
+ snapshot_file: "{{ inventory_hostname }}_routes.json"
You can also view unified diffs for GitHub pull requests by adding .diff to the URL of the pull request. This format makes it easy to see changes clearly and apply them automatically if needed.
HEAD
In Git, HEAD points to the latest commit in your current branch. You can refer to previous commits relative to HEAD using ~n, where n is the number of commits to go back.
HEAD~1➔ One commit before the latestHEAD~2➔ Two commits before the latestHEAD~3➔ Three commits before the latest
For example:
git show HEAD~3
This shows details of the commit three steps before HEAD.
When you run:
git log --oneline
Git displays a compact history of commits in the current branch. Each commit shows:
- A short commit hash (a unique identifier for the commit)
- The commit message
Example output:
a1b2c3d4 Add user authentication feature
e5f6g7h8 Fix database connection issue
i9j0k1l2 Update API endpoint response format
m3n4o5p6 Initial project setup
What happens:
- The latest commit appears at the top.
- Each line represents one commit in chronological order from newest to oldest.
- It’s a quick way to see the project’s commit history without all the detailed metadata.
You can use this output to reference commits in commands like git show <commit> or git diff <commit>.
git annotate
This is used to show who last modified each line of a file along with commit details.
git annotate test-file.md
Sample output:
a1b2c3d4 (Alice 2024-02-10 08:30:12 +0000 1) # Initial commit
a1b2c3d4 (Alice 2024-02-10 08:30:12 +0000 2) Added authentication module
e5f6g7h8 (Bob 2024-02-11 14:15:47 +0000 3) Refactored database connection
i9j0k1l2 (Charlie 2024-02-12 16:50:33 +0000 4) Updated API response format
git blame
Similar to git annotate, but is the standard command for tracking line modifications.
git blame test-file.md
Sample output:
a1b2c3d4 (Alice 2024-02-10 08:30:12 +0000 1) # Initial commit
a1b2c3d4 (Alice 2024-02-10 08:30:12 +0000 2) Added authentication module
e5f6g7h8 (Bob 2024-02-11 14:15:47 +0000 3) Refactored database connection
i9j0k1l2 (Charlie 2024-02-12 16:50:33 +0000 4) Updated API response format
Removing Files in Git
Using git rm
The git rm command removes files both the working directory and staging area. It stages the change for the next commit.
Note: <file-path> can be an absolute or relative path
git rm <file-path-1> ... <file-path-n>
To remove a file from the repository but keep it in your working directory:
git rm --cached <file-path-1> ... <file-path-n>
Using filesystem commands
You can also delete files manually and then stage the removal:
rm <file-path-1> ... <file-path-n>
git add <file-path-1> ... <file-path-n>
This achieves the same result as git rm, but does not allow you to keep the files in the working directory.
Unstaging changes
Undo changes before committing by resetting files from the staging area.
git reset HEAD sample-report.csv
To unstage all files:
git reset HEAD
Undo changes to unstaged file
Discard changes made to a file before staging. This is also the same command used to revert the file to an old version.
git checkout -- sample-report.csv
git checkout reverts a file to its last committed version.
This action is irreversible. Changes will be lost permanently.
To undo changes in all unstaged files:
git checkout .
To revert to a version from a specific commit:
git checkout asdety890 sample-report.csv ## asdety890 is the hash
To restore the entire repo to a previous state, specify the commit without specifying any file.
git checkout 123hjklsd ## 123hjklsd is the hash
Cleaning the repository
To see which files are not being tracked:
git clean -n
Next, proceed to deleting those files:
git clean -f
⚠️ This action is irreversible - files will be removed for good.