Index: commit-id
===================================================================
--- 6ad600e20c89323c1d3049f75b8ca9b0a2d72167/commit-id  (mode:100755 sha1:4efcb6bdfdb2b2c5744f5d4d47d92beb7777ed59)
+++ uncommitted/commit-id  (mode:100775)
@@ -1,39 +1,25 @@
 #!/usr/bin/env bash
 #
 # Get ID of commit associated with given id or HEAD.
+#
 # Copyright (c) Petr Baudis, 2005
 #
-# Takes the appropriate ID, defaults to HEAD.
-
-SHA1="[A-Za-z0-9]{40}"
-SHA1ONLY="^$SHA1$"
-
-id=$1
-if [ ! "$id" ] || [ "$id" = "this" ] || [ "$id" = "HEAD" ]; then
-	id=$(cat .git/HEAD)
-fi
 
-if (echo $id | egrep -vq "$SHA1ONLY") && [ -r ".git/refs/tags/$id" ]; then
-	id=$(cat ".git/refs/tags/$id")
-fi
-
-if (echo $id | egrep -vq "$SHA1ONLY") && [ -r ".git/refs/heads/$id" ]; then
-	id=$(cat ".git/refs/heads/$id")
-fi
+# Save for later error message
+orig="$1"
 
-idpref=$(echo "$id" | cut -c -2)
-idpost=$(echo "$id" | cut -c 3-)
-if [ $(find ".git/objects/$idpref" -name "$idpost*" 2>/dev/null | wc -l) -eq 1 ]; then
-	id=$idpref$(basename $(echo .git/objects/$idpref/$idpost*))
-fi
+# Normalize to SHA1 form
+id=$(cg-Xnormid "$orig")
 
-if echo $id | egrep -vq "$SHA1ONLY"; then
-	echo "Invalid id: $id" >&2
+if [ ! "$id" ]; then
+	# cg-Xnormid already reported the error
 	exit 1
 fi
 
-if [ "$(cat-file -t "$id")" != "commit" ]; then
-	echo "Invalid id: $id" >&2
+# cat-file will verify that $id is a valid SHA1 ID for us
+# If it isn't, we'll get '' back
+if [ "$(cat-file -t "$id" 2>/dev/null)" != "commit" ]; then
+	echo "Invalid commit id: $orig" >&2
 	exit 1
 fi