GIT : how to see who has changed what in a specific file ?

To see who has changed what in a specific file, you can use the git blame command followed by the file name. This will show you the commit hash, author, and date for each line in the file, as well as the content of the line and the commit message.

Example:

git blame myfile.txt

This will output something like:

^3d6a1b2 (John Doe 2021-01-01 10:00:00 -0500 1) This is the first line
^3d6a1b2 (John Doe 2021-01-01 10:00:00 -0500 2) This is the second line
^7b3c4d5 (Jane Smith 2021-01-02 11:00:00 -0500 3) This is the third line
^7b3c4d5 (Jane Smith 2021-01-02 11:00:00 -0500 4) This is the fourth line

In this example, John Doe made the first two changes to the file in commit 3d6a1b2, and Jane Smith made the next two changes in commit 7b3c4d5.