Is there a way to trigger a hook after a new branch has been checked out in Git?

Question

Is there a way to trigger a hook after a new branch has been checked out in Git?

Answer 1

If one of these hooks won’t do it I’d be amazed:

https://schacon.github.io/git/githooks.html

Maybe this one:

post-checkout

This hook is invoked when a git-checkout is run after having updated the worktree. The hook is given three parameters: the ref of the previous HEAD, the ref of the new HEAD (which may or may not have changed), and a flag indicating whether the checkout was a branch checkout (changing branches, flag=1) or a file checkout (retrieving a file from the index, flag=0). This hook cannot affect the outcome of git-checkout.

Answer 2

A git hook is a script placed in a special location of your repository, that location is:

.git/hooks

The script can be any kind that you can execute in your environment i.e. bash, python, ruby etc.

The hook that is executed after a checkout is post-checkout. From the docs:

...The hook is given three parameters...

Example:

1. Create the hook (script):

   touch .git/hooks/post-checkout
   chmod u+x .git/hooks/post-checkout
   

2. Hook sample content:

#!/bin/bash                                                                      

set -e                                                                           

printf '\npost-checkout hook\n\n'                                                

prevHEAD=$1                                                                      
newHEAD=$2                                                                       
checkoutType=$3                                                                  

[[ $checkoutType == 1 ]] && checkoutType='branch' ||                             
                            checkoutType='file' ;                                

echo 'Checkout type: '$checkoutType                                              
echo '    prev HEAD: '`git name-rev --name-only $prevHEAD`                       
echo '     new HEAD: '`git name-rev --name-only $newHEAD`

Note: The shebang in the first line indicates the type of script.

This script (git hook) will only capture the three parameters passed and print them in a human-friendly format.

Answer 3

Similar to others but verifies that the branch has been checked out once.

#!/bin/bash

# this is a file checkout – do nothing
if [ "$3" == "0" ]; then exit; fi

BRANCH_NAME=$(git symbolic-ref --short -q HEAD)
NUM_CHECKOUTS=`git reflog --date=local | grep -o ${BRANCH_NAME} | wc -l`

#if the refs of the previous and new heads are the same 
#AND the number of checkouts equals one, a new branch has been created
if [ "$1" == "$2"  ] && [ ${NUM_CHECKOUTS} -eq 1 ]; then
    git push origin ${BRANCH_NAME}
fi

Answer 4

The post-checkout hook receives three parameters:

1. Ref of previous HEAD
2. Ref of new HEAD
3. Whether this is a file checkout (0) or branch checkout (1)

You can use the fact that a branch created from the current HEAD will have the same value for parameters 1 and 2.

cat > .git/hooks/post-checkout <<"EOF"
if [ "$3" == "0" ]; then exit; fi
if [ "$1" == "$2" ]; then 
  echo "New branch created. (Probably)."
fi
EOF

chmod u+x .git/hooks/post-checkout

Limitations:

• Checking out an existing branch which happens to be at the same HEAD as the current HEAD will fool it.
• Creating a new branch not from the current HEAD will not be detected.