git/git-branch-script

#!/bin/sh

. git-sh-setup-script || die "Not a git archive"

branchname="$1"
rev=$(git-rev-parse --verify --default HEAD "$2"^0) || exit

[ -z "$branchname" ] && die "git branch: I want a branch name"
[ -e "$GIT_DIR/refs/heads/$branchname" ] && die "$branchname already exists"

echo $rev > "$GIT_DIR/refs/heads/$branchname"