Created some 600 template files with empty Google Maps API Key fields. These don't work anymore on several sites. Regenerating them with the proper API key would have been very tedious. So I used a single command for adding the proper key to existing templates:

find /home/Albums/NeueBilder/ -name Karte.htt -exec sed -i -e 's/google_api_key\ =\ '\'''\''/google_api_key\ =\ '\''A...........'\''/g' {} \;

The sed stream editor used for in place substitution is available for virtually any operating system.