Add git-{{local,remote}-branch,tag}-exists.

README.md

@@ -22,6 +22,21 @@ Accepts options, too, so you can use
 to force-push.
 
 
+### git is-headless
+
+Tests if `HEAD` is pointing to a branch head, or is detached.
+
+
+### git local-branch-exists / git remote-branch-exists / git tag-exists
+
+Tests if the given local branch, remote branch, or tag exists.
+
+
+### git is-headless
+
+Tests if `HEAD` is pointing to a branch head, or is detached.
+
+
 ### git is-merged-into
 
 Tests if X is merged into Y:
@@ -125,7 +140,7 @@ conflict.)
     * mybranch
 
 
-### git has-local-changes
+### git has-local-changes / git is-clean / git is-dirty
 
 Helper function that determines whether there are local changes in the working
 tree, by returning a 0 (local changes) or 1 (no local changes) exit code.

git-local-branch-exists

@@ -0,0 +1,17 @@
+#!/bin/sh
+set -e
+
+usage () {
+    echo "usage: git local-branch-exists <branch>" >&2
+    echo >&2
+    echo "Will return with an exit code of 0 or 1." >&2
+}
+
+if [ $# -eq 1 ]; then
+    branch=$1
+else
+    usage
+    exit 2
+fi
+
+git show-ref --heads --quiet --verify -- "refs/heads/$branch"

git-remote-branch-exists

@@ -0,0 +1,21 @@
+#!/bin/sh
+set -e
+
+usage () {
+    echo "usage: git remote-branch-exists [<remote>] <branch>" >&2
+    echo >&2
+    echo "Will return with an exit code of 0 or 1." >&2
+}
+
+if [ $# -eq 1 ]; then
+    remote=origin
+    branch=$1
+elif [ $# -eq 2 ]; then
+    remote=$1
+    branch=$2
+else
+    usage
+    exit 2
+fi
+
+git show-ref --quiet --verify -- "refs/remotes/$remote/$branch"

git-tag-exists

@@ -0,0 +1,17 @@
+#!/bin/sh
+set -e
+
+usage () {
+    echo "usage: git tag-exists <tag>" >&2
+    echo >&2
+    echo "Will return with an exit code of 0 or 1." >&2
+}
+
+if [ $# -eq 1 ]; then
+    tag=$1
+else
+    usage
+    exit 2
+fi
+
+git show-ref --tags --quiet --verify -- "refs/tags/$tag"