How can I get a side-by-side diff when I do "git diff"?

Although Git has an internal implementation of diff, you can set up an external tool instead.

There are two different ways to specify an external diff tool:

1. setting the GIT_EXTERNAL_DIFF and the GIT_DIFF_OPTS environment variables.
2. configuring the external diff tool via git config

ymattw's answer is also pretty neat, using ydiff

See also:

• https://git-scm.com/book/en/v2/Customizing-Git-Git-Configuration
• git diff --help
• http://www.pixelbeat.org/programming/diffs/

When doing a git diff, Git checks both the settings of above environment variables and its .gitconfig file.

By default, Git passes the following seven arguments to the diff program:

path  old-file  old-hex old-mode  new-file  new-hex new-mode

You typically only need the old-file and new-file parameters. Of course most diff tools only take two file names as an argument. This means that you need to write a small wrapper-script, which takes the arguments which Git provides to the script, and hands them on to the external git program of your choice.

Let's say you put your wrapper-script under ~/scripts/my_diff.sh:

#!/bin/bash
# un-comment one diff tool you'd like to use

# side-by-side diff with custom options:
# /usr/bin/sdiff -w200 -l "$2" "$5" 

# using kdiff3 as the side-by-side diff:
# /usr/bin/kdiff3 "$2" "$5"

# using Meld 
/usr/bin/meld "$2" "$5"

# using VIM
# /usr/bin/vim -d "$2" "$5"

you then need to make that script executable:

chmod a+x ~/scripts/my_diff.sh

you then need to tell Git how and where to find your custom diff wrapper script. You have three choices how to do that: (I prefer editing the .gitconfig file)

1. Using GIT_EXTERNAL_DIFF, GIT_DIFF_OPTS

   e.g. in your .bashrc or .bash_profile file you can set:

    GIT_EXTERNAL_DIFF=$HOME/scripts/my_diff.sh
    export GIT_EXTERNAL_DIFF
   

2. Using git config

   use "git config" to define where your wrapper script can be found:

    git config --global diff.external ~/scripts/my_diff.sh
   

3. Editing your ~/.gitconfig file

   you can edit your ~/.gitconfig file to add these lines:

    [diff]
      external = ~/scripts/my_diff.sh
   

Note:

Similarly to installing your custom diff tool, you can also install a custom merge-tool, which could be a visual merging tool to better help visualizing the merge. (see the progit.org page)

See: http://fredpalma.com/518/visual-diff-and-merge-tool/ and https://git-scm.com/book/en/v2/Customizing-Git-Git-Configuration

Try git difftool

Use git difftool instead of git diff. You'll never go back.

UPDATE to add an example usage:

Here is a link to another stackoverflow that talks about git difftool: How do I view 'git diff' output with my preferred diff tool/ viewer?

For newer versions of git, the difftool command supports many external diff tools out-of-the-box. For example vimdiff is auto supported and can be opened from the command line by:

cd /path/to/git/repo
git difftool --tool=vimdiff

Other supported external diff tools are listed via git difftool --tool-help here is an example output:

'git difftool --tool=<tool>' may be set to one of the following:
        araxis
        kompare
        vimdiff
        vimdiff2

The following tools are valid, but not currently available:
        bc3
        codecompare
        deltawalker
        diffuse
        ecmerge
        emerge
        gvimdiff
        gvimdiff2
        kdiff3
        meld
        opendiff
        tkdiff
        xxdiff