better version update script

update_version.sh

@@ -1,6 +1,19 @@
 #!/bin/bash
 
-VERSION=`git tag --sort=-taggerdate|head -1`
+VERSION=$1
+
+if [[ -z $VERSION ]]
+then
+    echo "Usage: $0 <version>"
+    echo "where <version> can be 1.0.4 or so"
+    exit 1
+fi
+
+if git tag --sort=-taggerdate | fgrep -q $VERSION
+then
+    echo Error: Tag $VERSION already exists.
+    exit 1
+fi
 
 function safe_move {
   local file1="$1" file2="$2"
@@ -29,4 +42,16 @@ safe_move build.sbt.new build.sbt
 
 # Check whether the version history has been updated, warn otherwise.
 
-grep -q "^- $VERSION " docs/roadmap.md || echo "Warning: docs/roadmap.md does not seem to have information about the current version $VERSION."
+if grep -q "^- $VERSION " docs/roadmap.md
+then
+    echo "Preparing new release $VERSION"
+else
+    echo "Error: docs/roadmap.md does not seem to have information about the current version $VERSION."
+    exit 1
+fi
+
+git add build.sbt README.md
+git commit -m "update for release $VERSION"
+git tag $VERSION
+
+echo "All done, now push to github using git push origin <branch> --tags"