Commit a file to another branch

git-commit-file-to-branch.sh

#!/bin/sh

BRANCH=$1
FILE=$2

if [ -z "$BRANCH" ]; then
    echo "Usage: $0 <branch> <file>"
    exit 1
fi

if [ ! -e "$FILE" ]; then
    echo "File does not exist:" $FILE
    exit 1
fi

if ((git diff --exit-code && git diff --cached --exit-code) > /dev/null); then
    :
else
    echo 'Index or working directory dirty'
    exit 1
fi

git read-tree refs/heads/$BRANCH
git update-index --add $FILE
TREE=$(git write-tree)
COMMIT=$(echo added file $FILE | git commit-tree $TREE -p refs/heads/$BRANCH)
echo 'Created commit:' $COMMIT

git update-ref refs/heads/$BRANCH $COMMIT
echo 'Updated branch:' $BRANCH

git reset HEAD
git clean -f $FILE
echo 'Cleaned up'