update-component-sha: Accept easier to cut-n-paste --image arguments.

Signed-off-by: Ian Campbell <ijc@docker.com>

scripts/update-component-sha.sh

@@ -23,6 +23,9 @@ Replace by image: $0 --image <IMAGE> <NEW>
 	Example: $0 --image linuxkit/foo abcdef567899
 	   Will tag all instances of linuxkit/foo with abcdef567899
 
+        $0 --image <IMAGE>:<NEW> is accepted as a convenient shortcut for cutting
+        and pasting e.g.the output of linuxkit pkg show-tag
+
 By default, for convenience, if no mode is given (--image or --hash), the first method (--hash) is assumed. 
 Thus the following are equivalent:
 	$0 <OLD> <NEW>
@@ -33,28 +36,39 @@ EOF
 
 
 # backwards compatibility
-if [ $# -eq 2 ]; then
+if [ $# -eq 2 -a -n "${1%--*}" ]; then
   set -- "--hash" "$1" "$2"
 fi
 
 # sufficient arguments
-if [ $# -ne 3 ] ; then
+if [ $# -lt 2 -o $# -gt 3 ] ; then
     usage
     exit 1
 fi
 
-
 # which mode?
 case "$1" in
     --hash)
+	if [ $# -ne 3 ] ; then
+	    usage
+	    exit 1
+	fi
         old=$2
         new=$3
 
         git grep -w -l "\b$old\b" | xargs sed -i.bak -e "s,$old,$new,g"
         ;;
     --image)
-        image=$2
-        hash=$3
+	case $# in
+	    2)
+		image=${2%:*}
+		hash=${2#*:}
+		;;
+	    3)
+		image=$2
+		hash=$3
+		;;
+	    esac
         git grep -E -l "\b$image:" | xargs sed -i.bak -e "s,$image:[[:xdigit:]]"'\{40\}'",$image:$hash,g"
         ;;
     *)