git undo all uncommitted or unsaved changes

What I do is

git add . (adding everything)
git stash 
git stash drop

One liner: git add . && git stash && git stash drop

A shorter version as pointed out by M. Justin

git stash -u && git stash drop

If you wish to "undo" all uncommitted changes simply run:

git stash
git stash drop

If you have any untracked files (check by running git status), these may be removed by running:

git clean -fdx

git stash creates a new stash which will become stash@{0}. If you wish to check first you can run git stash list to see a list of your stashes. It will look something like:

stash@{0}: WIP on rails-4: 66c8407 remove forem residuals
stash@{1}: WIP on master: 2b8f269 Map qualifications
stash@{2}: WIP on master: 27a7e54 Use non-dynamic finders
stash@{3}: WIP on blogit: c9bd270 some changes

Each stash is named after the previous commit messsage.

• This will unstage all files you might have staged with git add:

  git reset
  

• This will revert all local uncommitted changes (should be executed in repo root):

  git checkout .
  

  You can also revert uncommitted changes only to particular file or directory:

  git checkout [some_dir|file.txt]
  

  Yet another way to revert all uncommitted changes (longer to type, but works from any subdirectory):

  git reset --hard HEAD
  

• This will remove all local untracked files, so only git tracked files remain:

  git clean -fdx
  

  WARNING: -x will also remove all ignored files, including ones specified by .gitignore! You may want to use -n for preview of files to be deleted.

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To sum it up: executing commands below is basically equivalent to fresh git clone from original source (but it does not re-download anything, so is much faster):

git reset
git checkout .
git clean -fdx

Typical usage for this would be in build scripts, when you must make sure that your tree is absolutely clean - does not have any modifications or locally created object files or build artefacts, and you want to make it work very fast and to not re-clone whole repository every single time.