Archiving and Compression

     -r

If you want to use gzip on several files in a directory, just use a wildcard. You might not end up gzipping everything you think you will, however, as this example shows.

   $ ls -F
   bible/ moby-dick.txt paradise_lost.txt
   $ ls -l *
   -rw-r--r-- scott scott 1236574 moby-dick.txt
   -rw-r--r-- scott scott 508925 paradise_lost.txt

   bible:
   -rw-r--r-- scott scott 207254 genesis.txt
   -rw-r--r-- scott scott 102519 job.txt
   $ gzip *
   gzip: bible is a directory -- ignored
   $ ls -l *
   -rw-r--r-- scott scott 489609 moby-dick.txt.gz
   -rw-r--r-- scott scott 224425 paradise_lost.txt.gz

   bible:
   -rw-r--r-- scott scott 207254 genesis.txt
   -rw-r--r-- scott scott 102519 job.txt

Notice that the wildcard didn't do anything for the files inside the bible directory because gzip by default doesn't walk down into subdirectories. To get that behavior, you need to use the -r (or --recursive) option along with your wildcard.

   $ ls -F
   bible/ moby-dick.txt paradise_lost.txt
   $ ls -l *
   -rw-r--r-- scott scott 1236574 moby-dick.txt
   -rw-r--r-- scott scott 508925 paradise_lost.txt

   bible:
   -rw-r--r-- scott scott 207254 genesis.txt
   -rw-r--r-- scott scott 102519 job.txt
   $ gzip -r *
   $ ls -l *
   -rw-r--r-- scott scott 489609 moby-dick.txt.gz
   -rw-r--r-- scott scott 224425 paradise_lost.txt.gz

   bible:
   -rw-r--r-- scott scott 62114 genesis.txt.gz
   -rw-r--r-- scott scott 35984 job.txt.gz

This time, every file — even those in subdirectories — was gzipped. However, note that each file is individually gzipped. The gzip command cannot combine all the files into one big file, like you can with the zip command. To do that, you need to incorporate tar, as you'll see in "Archive and Compress Files with tar and 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 don't mind waiting a bit longer to get the job done." 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."

     gunzip

Getting files out of a gzipped archive is easy with the gunzip command.

   $ ls -l
   -rw-r--r-- scott scott 224425 paradise_lost.txt.gz
   $ gunzip paradise_lost.txt.gz
   $ ls -l
   -rw-r--r-- scott scott 508925 paradise_lost.txt

In the same way that gzip removes the original file, leaving you solely with the gzipped result, gunzip removes the .gz file, leaving you with the final gunzipped result. If you want to ensure that you have both, you need to use the -c option (or --stdout or --to-stdout) and pipe the results to the file you want to create.

   $ ls -l
   -rw-r--r-- scott scott 224425 paradise_lost.txt.gz
   $ gunzip -c paradise_lost.txt.gz > paradise_lost.txt
   $ ls -l
   -rw-r--r-- scott scott 508925 paradise_lost.txt
   -rw-r--r-- scott scott 224425 paradise_lost.txt.gz

It's probably a good idea to use -c, especially if you plan to keep behind the .gz file or pass it along to someone else. Sure, you could use gzip and create your own archive, but why go to the extra work?