user-manual: use pithier example commit

diff --git a/Documentation/git-update-ref.txt b/Documentation/git-update-ref.txt
index e062030e91ae2b2a25c2ef7bafc4c026015e1f5e..9424feab320afcaa5a44bd2c2c6c86728bd8d004 100644 (file)
--- a/Documentation/git-update-ref.txt
+++ b/Documentation/git-update-ref.txt
@@ -3,11 +3,11 @@ git-update-ref(1)
 
 NAME
 ----
-git-update-ref - update the object name stored in a ref safely
+git-update-ref - Update the object name stored in a ref safely
 
 SYNOPSIS
 --------
-'git-update-ref' [-m <reason>] <ref> <newvalue> [<oldvalue>]
+'git-update-ref' [-m <reason>] (-d <ref> <oldvalue> | <ref> <newvalue> [<oldvalue>])
 
 DESCRIPTION
 -----------
@@ -20,7 +20,9 @@ possibly dereferencing the symbolic refs, after verifying that
 the current value of the <ref> matches <oldvalue>.
 E.g. `git-update-ref refs/heads/master <newvalue> <oldvalue>`
 updates the master branch head to <newvalue> only if its current
-value is <oldvalue>.
+value is <oldvalue>.  You can specify 40 "0" or an empty string
+as <oldvalue> to make sure that the ref you are creating does
+not exist.
 
 It also allows a "ref" file to be a symbolic pointer to another
 ref file by starting with the four-byte header sequence of
@@ -49,6 +51,10 @@ for reading but not for writing (so we'll never write through a
 ref symlink to some other tree, if you have copied a whole
 archive by creating a symlink tree).
 
+With `-d` flag, it deletes the named <ref> after verifying it
+still contains <oldvalue>.
+
+
 Logging Updates
 ---------------
 If config parameter "core.logAllRefUpdates" is true or the file