How to delete postgresql databases matching a pattern?

psql -c "copy (select datname from pg_database where datname like '%june%') to stdout" | while read line; do
    echo "$line"
    #dropdb -i "$line"
done

Or using for loop which is more reliable (while block executed in the parent context so it is necessary to do some additional movements for its body):

for dbname in $(psql -c "copy (select datname from pg_database where datname like '%june%') to stdout") ; do
    echo "$dbname"
    #dropdb -i "$dbname"
done

Also option -X for psql (do not use ~/.psqlrc file) could be good to avoid unnecessary outputs.

For psql and dropdb utilities you probably need to provide the connection options (see documentation)