You can try this out. I did that a week back. But be informed that if the database can be taken offline for a short while, only then you can go for this solution, because it uses dettach and attach database methods for immediate effect in log file size.
Steps for Shrinking LOG space, if you run out of HDD space and want that to get effected immediately.
1) 'Removes the inactive part of the LOG without making a backup copy of it and truncates the log
BACKUP LOG <DB_NAME> WITH TRUNCATE_ONLY
2) 'Shrinks the size of the specified LOG file for the related database.
DBCC SHRINKFILE (<DB_NAME>_Log, 100) only in multiples of 100 MBs
3) 'To bring DB offline and get the shrunk LogFile size effected physically in the HDD
sp_detach_db <DB_NAME>, true
4) 'To bring the DB online.
sp_attach_db @dbname = N'<DB_NAME>',
@filename1 = N'C:\MSSQL\Data\<DB_NAME>_Data.MDF',
@filename2 = N'C:\MSSQL\Data\<DB_NAME>_Log.LDF'
NOTE: Replace all the <DB_NAME> with your database name.
Hope that helps.
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