How do I get the commit id of the head of master in git?

Question

I want to display the git commit id (i.e. SHA) of the head of master on my website as an identifier.

How can I pull this information from git?

Answer 1

This command will get you the latest commit's SHA-1

git rev-parse HEAD 

Answer 2

Instead of the HEAD SHA1, I would rather go with git describe, as a more readable way to get a "build id". For instance:

git describe --abbrev=4 HEAD 

---

If you don't care about tags, and considering that git describe is a porcelain command, which shouldn't be used in a script, then, yes, git rev-parse (a plumbing command) is more appropriate.

But again, if you are to display a SHA1 on your website as an id, I would go with:

git rev-parse --short HEAD 

(In order to display only the first 7 digits of the SHA1)

---

git rev-parse HEAD (meaning the all 40 digits) is still useful, when you want to check if what you just deployed is indeed what HEAD refers to.
See for instance this deployment script:

It first triggers an update:

#If requested, perform update before gathering information from repos. if $update; then     echo "Updating fred-official."     cd "$fredDir"     git_update     if ! [[ "$forceFredID" = "" ]]     then         checkGitID "$forceFredID"     fi     echo "Updating website repo."     cd "$websiteDir"     git_update     if ! [[ "$forceWebsiteID" = "" ]]     then         checkGitID "$forceWebsiteID"     fi     cd "$startingDir" fi 

The update itself refreshes the website content:

# Discard any local changes, update remote branches and tags, and # check out to the latest master branch. git_update() {     #To update tags and branches.     git remote update     git clean -dfx     git reset --hard origin/master } 

And then it uses git rev-parse HEAD to check what just has been checked out:

function checkGitID {     checkID=$1     echo Checking git ID is "$checkID"     if ! git checkout "$checkID"     then         echo Failed to checkout "$checkID"         exit 4     fi     if ! actualID=$(git rev-parse --verify HEAD)     then         echo Failed to verify "$checkID"         git checkout master         exit 5     fi     if ! [[ "$actualID" = "$checkID" ]]     then         echo Git verification failed, something very bad is happening         exit 6     fi     echo Git ID verified: "$checkID" }