How do I get the hash for the current commit in Git?

To turn any extended object reference into a hash, use git-rev-parse:

git rev-parse HEAD

or

git rev-parse --verify HEAD

To retrieve the short hash:

git rev-parse --short HEAD

To turn references (e.g. branches and tags) into hashes, use git show-ref and git for-each-ref.

Use git rev-list --max-count=1 HEAD

git rev-parse HEAD does the trick.

If you need to store it to checkout back later than saving actual branch if any may be preferable:

cat .git/HEAD

Example output:

ref: refs/heads/master

Parse it:

cat .git/HEAD | sed "s/^.\+ \(.\+\)$/\1/g"

If you have Windows then you may consider using wsl.exe:

wsl cat .git/HEAD | wsl sed "s/^.\+ \(.\+\)$/\1/g"

Output:

refs/heads/master

This value may be used to git checkout later but it becomes pointing to its SHA. To make it to point to the actual current branch by its name do:

wsl cat .git/HEAD | wsl sed "s/^.\+ \(.\+\)$/\1/g" | wsl sed "s/^refs\///g"  | wsl sed "s/^heads\///g"

Output:

master

Here is one-liner in Bash shell using direct read from git files:

(head=($(<.git/HEAD)); cat .git/${head[1]})

^{You need to run above command in your git root folder.}

This method can be useful when you've repository files, but git command has been not installed.

If won't work, check in .git/refs/heads folder what kind of heads do you have present.

On git bash, simply run $ git log -1

you will see, these lines following your command.

commit d25c95d88a5e8b7e15ba6c925a1631a5357095db .. (info about your head)

d25c95d88a5e8b7e15ba6c925a1631a5357095db, is your SHA for last commit.

Pretty print of main git repo, and sub-modules:

echo "Main GIT repo:"
echo $(git show -s --format=%H) '(main)'
echo "Sub-modules:"
git submodule status | awk '{print $1,$2}'

Example output:

3a032b0992d7786b00a8822bbcbf192326160cf9 (main)
7de695d58f427c0887b094271ba1ae77a439084f sub-module-1
58f427c0887b01ba1ae77a439084947de695d27f sub-module-2
d58f427c0887de6957b09439084f4271ba1ae77a sub-module-3

How I would do it in python (based on @kenorb's bash answer)

def get_git_sha():
    # Which branch are we on?
    branch = open(".git/HEAD", "r").read()

    # Parse output "ref: refs/heads/my_branch" -> my_branch
    branch = branch.strip().split("/")[-1]

    # What's the latest commit in this branch?
    return open(f".git/refs/heads/{branch}").read().strip()

echo "printing last commit id# for current branch:";

 git reflog