How can you use git diff to see only the modifications in the content, ignoring additions and deletions?

Git is a powerful version control system that developers use to track changes in their code over time. One of its key features is the ability to show differences between different versions of a codebase using the git diff command. By default, this command shows all changes between the two specified states, including additions, deletions, and modifications. But in certain scenarios, you may want to ignore additions and deletions and focus only on modifications.

To achieve this, you would need to use a combination of the git diff command and other Unix commands like grep and sed. The following is an example of a command that will provide a diff of only modifications, ignoring additions and deletions:

git diff --color | grep '^\s\|^[-][^-]\|^commit\|^Author\|^Date\|^+++\|^---'

Let’s break down this command:

  1. git diff --color : This command generates the diff output. The --color option is used to colorize the output, making it easier to read and understand.
  2. | : This is a pipe. It is used to send the output of one command (in this case, git diff --color) as the input to another command (in this case, grep).
  3. grep '^\s\|^[-][^-]\|^commit\|^Author\|^Date\|^+++\|^---' : This command filters the input it receives. The argument is a regular expression that matches any line that begins with a space (representing a modification), a single dash (representing a context line), or any of the header lines (like ‘commit’, ‘Author’, ‘Date’, etc).

Please note that the aforementioned command will not work if you’re working with a language that utilizes - as part of the syntax. The command is also sensitive to the format of the git diff output and can be affected by different git settings.

The command displays the modifications in the context of a few unchanged lines (depending on your configuration) to give an idea about where the changes were made. The changed lines are shown with a - for the original line and a + for the changed line.

If you only want to see the modified lines and not the context or the headers, you could use the following command:

git diff | grep '^[+-]' | grep -Ev '^(--- a/|\+\+\+ b/)'

This command excludes the lines starting with --- a/ or +++ b/, which are part of the diff header.

However, please remember that using Git in this way is more of a workaround than a feature. The intention behind Git is to track changes, including additions and deletions. So using it only for modifications might not give you the full picture of what’s happening in your codebase.