If you ever need to upgrade a code base to Puppet 3.0 and strip all dynamic scoping from your templates: 
for file in $( find . -name "*.erb" | sort); do 
    echo "------------ [ $file ]"; 
    if grep -q "<%[^>]*$" $file; then 
        content=$(sed '/<%/,/%>/!d' $file); 
    else
        content=$(grep "<%" $file); 
    fi;
    echo "$content" | egrep "(.each|if |%=)" | egrep -v "scope.lookupvar|@|scope\["; 
done
This is of course just a fuzzy match, but should catch quite some of the dynamic scope expressions there are. The limits of this solution are:
  • false positives on loop and declared variables that must not be scoped
  • and false negatives when mixing of correct scope and missing scope in the same line.
So use with care.