Description: compresses or un-compresses files. The level option specifies the compression mode to use when compressing. Available modes are from 0 (minimum CPU usage, minimum compression) all the way up to 9 (maximum CPU usage, maximum compression). If you don't specify the target-file, the src-file will be overwritten.
Description: determines whether <filename> is gzip compressed. Returns 1 if it is, 0 if it isn't, and 2 if some kind of error prevented the checks from succeeding.