How do I know the gzip compression level?

Question

Given a gzip compressed file, how do I know what compression level (1-9) was used for it?

score 37 · Answer 1 · answered Jun 16 '14 at 21:59

It is stored in the header of file. To see it, use file command. For example:

$ file testfile.gz
testfile.gz: gzip compressed data, from Unix, last modified: Sun Sep 15 14:22:19 2013, max compression

Unfortunately there are only three possible values in the header: max speed (level 1), max compression (level 9) and "normal" (all other levels). But better than nothing!

score 9 · Answer 2 · answered Apr 12 '11 at 17:25

9

gzip -l <filename> will give you the compression ratio, but there's no way of directly finding the compression level used.

answered Apr 12 '11 at 17:25

Andrew Lambert

7,805

score 7 · Accepted Answer · answered Apr 12 '11 at 16:31

There is no way to directly determine gzip level .
The only way to determine it in my opinion is to gunzip the file and compressing it at different levels and then comparing the results with your existing file size.
I believe the default level is 6 so in most cases that should be your answer

score 2 · Answer 4 · edited May 23 '17 at 12:41

2

There is no direct way of knowing it. It most probably 6 (the current default) or 9 (the best compression). you need to try and compare.

See https://stackoverflow.com/questions/16153334/how-to-determine-the-compression-level-of-deflate

edited May 23 '17 at 12:41

Community

1

answered May 22 '13 at 13:41

kolistivra

357

How do I know the gzip compression level?

4 Answers4