Difference between file in local repository and origin

Question

If [remote-path] and [local-path] are the same, you can do

$ git fetch origin master
$ git diff origin/master -- [local-path]

Note 1: The second command above will compare against the locally stored remote tracking branch. The fetch command is required to update the remote tracking branch to be in sync with the contents of the remote server. Alternatively, you can just do

$ git diff master:<path-or-file-name>

Note 2: master can be replaced in the above examples with any branch name

To view the differences going from the remote file to the local file:

git diff remotename/branchname:remote/path/file1.txt local/path/file1.txt

To view the differences in the other direction:

git diff HEAD:local/path/file1.txt remotename/branchname:remote/path/file1.txt

Basically you can diff any two files anywhere using this notation:

git diff ref1:path/to/file1 ref2:path/to/file2

As usual, ref1 and ref2 could be branch names, remotename/branchname, commit SHAs, etc.

To compare the local repository with the remote one, simply use the below syntax:

git diff @{upstream}

For that I wrote a Bash script:

#set -x
branchname=`git branch | grep -F '*' |  awk '{print $2}'`
echo $branchname
git fetch origin ${branchname}
for file in `git status | awk '{if ($1 == "modified:") print $2;}'`
do
echo "PLEASE CHECK OUT GIT DIFF FOR "$file
git difftool  FETCH_HEAD $file ;
done

In the above script, I fetch the remote main branch (not necessarily its master branch - any branch) to FETCH_HEAD, make a list of my modified file only, and compare modified files to git difftool.

There are many difftool supported by Git, I configured Meld Diff Viewer for good GUI comparison.

From the above script, I have prior knowledge what changes done by other teams in the same file before I follow the Git stages untracked → staged → commit, which help me to avoid unnecessary resolve merge conflict with a remote team or make a new local branch and compare and merge on the main branch.

I tried a couple of solutions, but I think an easy way is like this (you are in the local folder):

#!/bin/bash
git fetch

var_local=`cat .git/refs/heads/master`
var_remote=`git log origin/master -1 | head -n1 | cut -d" " -f2`

if [ "$var_remote" = "$var_local" ]; then
    echo "Strings are equal." #1
else
    echo "Strings are not equal." # 0 if you want
fi

After running this script, you will be finished comparing the local Git and remote Git using the last commit number.