1 files changed, 138 insertions, 0 deletions
diff --git a/git-checkout.sh b/git-checkout.sh
new file mode 100755
index 0000000000..4cf30e2c05
--- /dev/null
+++ b/git-checkout.sh
@@ -0,0 +1,138 @@
+#!/bin/sh
+. git-sh-setup
+
+usage () {
+    die "usage: git checkout [-f] [-b <new_branch>] [<branch>] [<paths>...]"
+}
+
+old=$(git-rev-parse HEAD)
+new=
+force=
+branch=
+newbranch=
+while [ "$#" != "0" ]; do
+    arg="$1"
+    shift
+    case "$arg" in
+	"-b")
+		newbranch="$1"
+		shift
+		[ -z "$newbranch" ] &&
+			die "git checkout: -b needs a branch name"
+		[ -e "$GIT_DIR/refs/heads/$newbranch" ] &&
+			die "git checkout: branch $newbranch already exists"
+		git-check-ref-format "heads/$newbranch" ||
+			die "we do not like '$newbranch' as a branch name."
+		;;
+	"-f")
+		force=1
+		;;
+	--)
+		break
+		;;
+	-*)
+		usage
+		;;
+	*)
+		if rev=$(git-rev-parse --verify "$arg^0" 2>/dev/null)
+		then
+			if [ -z "$rev" ]; then
+				echo "unknown flag $arg"
+				exit 1
+			fi
+			new="$rev"
+			if [ -f "$GIT_DIR/refs/heads/$arg" ]; then
+				branch="$arg"
+			fi
+		elif rev=$(git-rev-parse --verify "$arg^{tree}" 2>/dev/null)
+		then
+			# checking out selected paths from a tree-ish.
+			new="$rev"
+			branch=
+		else
+			new=
+			branch=
+			set x "$arg" "$@"
+			shift
+		fi
+		break
+		;;
+    esac
+done
+
+# The behaviour of the command with and without explicit path
+# parameters is quite different.
+#
+# Without paths, we are checking out everything in the work tree,
+# possibly switching branches.  This is the traditional behaviour.
+#
+# With paths, we are _never_ switching branch, but checking out
+# the named paths from either index (when no rev is given),
+# or the named tree-ish (when rev is given).
+
+if test "$#" -ge 1
+then
+	if test '' != "$newbranch$force"
+	then
+		die "updating paths and switching branches or forcing are incompatible."
+	fi
+	if test '' != "$new"
+	then
+		# from a specific tree-ish; note that this is for
+		# rescuing paths and is never meant to remove what
+		# is not in the named tree-ish.
+		git-ls-tree -r "$new" "$@" |
+		git-update-index --index-info || exit $?
+	fi
+	git-checkout-index -f -u -- "$@"
+	exit $?
+else
+	# Make sure we did not fall back on $arg^{tree} codepath
+	# since we are not checking out from an arbitrary tree-ish,
+	# but switching branches.
+	if test '' != "$new"
+	then
+		git-rev-parse --verify "$new^{commit}" >/dev/null 2>&1 ||
+		die "Cannot switch branch to a non-commit."
+	fi
+fi
+
+[ -z "$new" ] && new=$old
+
+# If we don't have an old branch that we're switching to,
+# and we don't have a new branch name for the target we
+# are switching to, then we'd better just be checking out
+# what we already had
+
+[ -z "$branch$newbranch" ] &&
+	[ "$new" != "$old" ] &&
+	die "git checkout: you need to specify a new branch name"
+
+if [ "$force" ]
+then
+    git-read-tree --reset $new &&
+	git-checkout-index -q -f -u -a
+else
+    git-update-index --refresh >/dev/null
+    git-read-tree -m -u $old $new
+fi
+
+# 
+# Switch the HEAD pointer to the new branch if it we
+# checked out a branch head, and remove any potential
+# old MERGE_HEAD's (subsequent commits will clearly not
+# be based on them, since we re-set the index)
+#
+if [ "$?" -eq 0 ]; then
+	if [ "$newbranch" ]; then
+		leading=`expr "refs/heads/$newbranch" : '\(.*\)/'` &&
+		mkdir -p "$GIT_DIR/$leading" &&
+		echo $new >"$GIT_DIR/refs/heads/$newbranch" || exit
+		branch="$newbranch"
+	fi
+	[ "$branch" ] &&
+	GIT_DIR="$GIT_DIR" git-symbolic-ref HEAD "refs/heads/$branch"
+	rm -f "$GIT_DIR/MERGE_HEAD"
+else
+	exit 1
+fi