The most popular Unix File compression command is
gzip repalces the original file with a compressed version, which has a .gz file extension.
$ ls -l -rw-r--r-- 1 JohnDoe staff 285 May 9 13:27 README.md -rw-r--r-- 1 JohnDoe staff 6459 May 9 13:27 index.html -rw-r--r-- 1 JohnDoe staff 5341 May 9 13:27 todo.txt $ gzip README.md todo.txt index.html $ ls -l -rw-r--r-- 1 JohnDoe staff 56 May 9 13:27 README.md.gz -rw-r--r-- 1 JohnDoe staff 2626 May 9 13:27 index.html.gz -rw-r--r-- 1 JohnDoe staff 2113 May 9 13:27 todo.txt.gz
As you can see, the files have been individually compressed. Note, however, that you can't
gzip a folder.
To reverse a file back to its uncompressed form, use
gunzip. The uncompressed file will have the same permissionas and timestamp as when it was gzipped.
$ gunzip README.md index.html todo.txt -rw-r--r-- 1 JohnDoe staff 285 May 9 13:27 README.md -rw-r--r-- 1 JohnDoe staff 6459 May 9 13:27 index.html -rw-r--r-- 1 JohnDoe staff 5341 May 9 13:27 todo.txt
Note how we don't need to specify the .gz in the filename, as that is already assumed.
There are several options you can use with
gzip. Here are a list of the most common ones - be sure to check the man page for more.
Suppose you want to keep the original files, and make an extra copy for the gzipped ones. Simply pass in the
$ gzip -k README.md $ ls ... README.md README.md.gz ...
We can view the compression ratio with the
$ gzip index.html.gz $ gzip -l index.html.gz compressed uncompressed ratio uncompressed_name 2626 6459 59.3% index.html $ gzip -l README.md.gz compressed uncompressed ratio uncompressed_name 56 285 80.3% README.md
Seeing our ratio, we can tell that our README.md file must have a lot of repeated elements!
zcat is the same as using
gunzip -c. It will unzip your file and print to standard out.
$ zcat README.md.gz | less # unzipped and now you can read with less $ zless # same function as above
Make sure you don't compress an already compressed format. File types such as .mp3 and .jpeg have already been compressed, so a further compression may cause the file to become larger.
As you can tell,
gzip was not meant to compress a group of multiple files - we use the
tar command for that, which we'll see in the next lesson.
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