If you are fine using a graphical tool (or even prefer it) you can:
gitk pom.xml
In gitk you can then click any commit (to "select" it) and right click any other commit to select "Diff this -> selected" or "Diff selected -> this" in the popup menu, depending on what order you prefer.
git diff master~20 -- pom.xml
Works if you are not in master branch too.
git diff <revision> <path>
For example:
git diff b0d14a4 foobar.txt
If neither commit is your HEAD then bash's brace expansion proves really useful, especially if your filenames are long, the example above:
git diff master~20:pom.xml master:pom.xml
Would become
git diff {master~20,master}:pom.xml
More on Brace expansion with bash.
For people interested in doing the same from GitHub, see comparing commits across time.
Generic Syntax :
$git diff oldCommit..newCommit -- **FileName.xml > ~/diff.txt
for all files named "FileName.xml" anywhere in your repo.
Notice the space between "--" and "**"
Answer for your question:
$git checkout master
$git diff oldCommit..HEAD -- **pom.xml
or
$git diff oldCommit..HEAD -- relative/path/to/pom.xml
as always with git, you can use a tag/sha1/"HEAD^" to id a commit.
Tested with git 1.9.1 on Ubuntu.
If you need to diff on a single file in a stash for example you can do
git diff stash@{0} -- path/to/file
To see what was changed in a file in the last commit:
git diff HEAD~1 path/to/file
You can change the number (~1) to the n-th commit which you want to diff with.
For comparing to 5 commit to the current one, both on master, just simply do:
git diff master~5:pom.xml master:pom.xml
Also you can refer to commit hash number, for example if the hash number is x110bd64, you can do something like this to see the difference:
git diff x110bd64 pom.xml
If you want to see the difference between the last commit of a single file you can do:
git log -p -1 filename
This will give you the diff of the file in git, is not comparing your local file.
If you are looking for the diff on a specific commit and you want to use the github UI instead of the command line (say you want to link it to other folks), you can do:
https://github.com/<org>/<repo>/commit/<commit-sha>/<path-to-file>
For example:
Note the Previous and Next links at the top right that allow you to navigate through all the files in the commit.
This only works for a specific commit though, not for comparing between any two arbitrary versions.
git diff -w HEAD origin/master path/to/file
Source: Stackoverflow.com