Scott Granneman

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Chapter 8: Archiving & Compression

The following were removed from Chapter 8: “Archiving & Compression”.

Get the Best Compression Possible with gzip ↩

gzip -[0-9]

Just as with zip, it’s possible to adjust the level of compression that gzip uses when it does its job. The gzip command uses a scale from 0 to 9, in which 0 means “no compression at all” (which is like tar, as you’ll see later), 1 means “do the job quickly, but don’t bother compressing very much,” and 9 means “compress the heck out of the files, and I’ll wait as long as I need to”. The default is 6, but modern computers are fast enough that it’s probably just fine to use 9 all the time.

$ ls -l
-rw-r--r-- scott scott 1236574 moby-dick.txt
$ gzip -c -1 moby-dick.txt > moby-dick.txt.gz
$ ls -l
-rw-r--r-- scott scott 1236574 moby-dick.txt
-rw-r--r-- scott scott  571005 moby-dick.txt.gz
$ gzip -c -9 moby-dick.txt > moby-dick.txt.gz
$ ls -l
-rw-r--r-- scott scott 1236574 moby-dick.txt
-rw-r--r-- scott scott  487585 moby-dick.txt.gz

Remember to use the -c option and pipe the output into the actual .gz file due to the way gzip works, as discussed in “Archive and Compress Files Using gzip.”

Note ↩

If you want to be clever, define an alias in your .bash_aliases file that looks like this:

alias gzip='gzip -9'

That way, you’ll always use -9 and won’t have to think about it.

Get the Best Compression Possible with bzip2 ↩

bzip2 -[0-9]

Just as with zip and gzip, it’s possible to adjust the level of compression that bzip2 uses when it does its job. The bzip2 command uses a scale from 0 to 9, in which 0 means “no compression at all” (which is like tar, as you’ll see later), 1 means “do the job quickly, but don’t bother compressing very much,” and 9 means “compress the heck out of the files, and I’ll wait as long as I need to”. The default is 6, but modern computers are fast enough that it’s probably just fine to use 9 all the time.

$ ls -l
-rw-r--r-- scott scott 1236574 moby-dick.txt
$ bzip2 -k -1 moby-dick.txt
$ ls -l
-rw-r--r-- scott scott 1236574 moby-dick.txt
-rw-r--r-- scott scott  424084 moby-dick.txt.bz2
$ bzip2 -k -9 moby-dick.txt
$ ls -l
-rw-r--r-- scott scott 1236574 moby-dick.txt
-rw-r--r-- scott scott  367248 moby-dick.txt.bz2

From 424KB with 1 to 367KB with 9—that’s quite a difference! Also notice the difference in ultimate file size between gzip and bzip2. At -9, gzip compressed moby-dick.txt down to 488KB, while bzip2 mashed it even further to 367KB. The bzip2 command is noticeably slower than the gzip command, but on a fast machine that means that bzip2 takes two or three seconds longer than gzip, which frankly isn’t much to worry about.

Note ↩

If you want to be clever, define an alias in your .bash_aliases file that looks like this:

alias bzip2='bzip2 -9'

That way, you’ll always use -9 and won’t have to think about it.

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