How do i undo my change in a git file?

giraffelife

Let's say you made a change to a file and committed it, and now you want to undo the change.

Here's all your changes and the diff between current and previous commit, i.e. before you added the Fifth line, and you now want to undo the Fifth line.

$ git log --oneline
cc9e080 I want to keep the changes to my fith line
08c6bb5 My Super duper forth line message
afa0b05 More than one line this is another line
dbaade7 Added a second line to my file
2561e02 Initial commit of repository

$ git diff 08c6bb5
diff --git a/README.md b/README.md
index 4ba7d0a..9f28333 100644
--- a/README.md
+++ b/README.md
@@ -5,3 +5,5 @@ Second Line: When I get back from running I'm tired
 Third Line: I got straight to bed
 
 Fourth Line: and I dream of running the marathon
+
+Fifth Line:  but I don't dress up in a silly costume I'm a serious runner

You use the git checkout command, which moved the HEAD to a position where you are happy with the file contents.

Remember you can use the commit hash or the HEAD~<number> to get to the commit you want

$ git checkout 08c6bb5 README.md

$ cat README.md 
First Line: Today i woke up and went running

Second Line: When I get back from running I'm tired

Third Line: I got straight to bed

Fourth Line: and I dream of running the marathon

NOTE: Be careful when doing checkouts, if you get the file names or hash numbers wrong or do not provide a file name to checkout, you can end up in what's know as a detached HEAD state.

You can see you're back to where the Fifth line did not exist. Git behind the scenes just made a new commit of the file, you can observe this by doing a git status

Before checkout the git status would have shown nothing to commit, and clean working directory

$ git status
On branch master
Changes to be committed:
  (use "git reset HEAD <file>..." to unstage)

	modified:   README.md

and diff shows a line being deleted from our file, instead of pluses symbols we got minus symbols now, showing the line(s) deleted.

$ git diff --staged
diff --git a/README.md b/README.md
index 9f28333..4ba7d0a 100644
--- a/README.md
+++ b/README.md
@@ -5,5 +5,3 @@ Second Line: When I get back from running I'm tired
 Third Line: I got straight to bed
 
 Fourth Line: and I dream of running the marathon
-
-Fifth Line:  but I don't dress up in a silly costume I'm a serious runner

and not just commit your file.

$ git commit -m "I didn't mean to add the last line, so deleted it"
[master f1f04a2] I didn't mean to add the last line, so deleted it
 1 file changed, 2 deletions(-)