The gzip command is a common way of compressing files within Linux.
By default when you compress a file or folder using the gzip command it will have the same file name as it did before but with the extension .gz.
The screenshots below apply to Ubuntu specifically, but the gzip command works on other Unix-like OSs, too.
How to Compress a File Using gzip
The simplest way to compress a single file using gzip is to run the following command:
gzip filename
To compress a file called mydocument.odt run the following command:
gzip mydocument.odt
If the file name contains spaces, surround it by quotes:
gzip "this is my file.png"
Some files compress better than others. For example documents, text files, bitmap images, and certain audio and video formats such as WAV and MPEG compress very well. Other file types such as JPEG images and MP3 audio files do not compress at all well and the file may actually increase in size after running the gzip command against it.
JPEG images and MP3 audio files are already compressed and therefore the gzip command simply adds to it rather than compressing it.
The gzip command only attempts to compress regular files and folders.
How to Decompress a File Using the gzip Command
Use the following command to decompress a gzip archive:
gzip -d filename.gz
To decompress the mydocument.odt.gz file use the following command:
gzip -d mydocument.odt.gz
Force a File to Be Compressed
Sometimes a file cannot be compressed. To force the gzip command to do its stuff simply run the following command:
gzip -f filename
How to Keep the Uncompressed File
By default when you compress a file using the gzip command you end up with a new file with the extension .gz. To compress the file and keep the original file must specify the -k flag:
gzip -k filename
I you run the following command you would end up with a file called mydocument.odt and mydocument.odt.gz.
gzip -k mydocument.odt
Get Some Stats About How Much Space You Saved
The whole point of compressing files is about saving disk space or to reduce the size of a file prior to sending it over a network. The gzip command provides the kind of statistics you require when checking for compression performance.
To get the list of statistics run the following command:
gzip -l filename.gz
In the above command, the option is a lowercase L, not a 1 or uppercase i.
The information returned by the above command is as follows:
- Compressed size
- Uncompressed size
- Ratio as a percentage
- Uncompressed filename
Compress Every File in a Folder and Subfolders
Compress every file in a folder and its subfolders by using the following command:
gzip -r foldername
This process doesn't create one file called foldername.gz. Instead, it traverses the directory structure and compresses each file in that folder structure.
To compress the folder structure as one file you are better off creating a tar file and then gzipping the tar file.
Use this command to decompress multiple files:
gzip -d *.gz
How to Test the Validity of a Compressed File
To verify that a file is valid, run the following command:
gzip -t filename
If the file is valid there will be no output.
How to Change the Compression Level
You can compress a file in different ways. For example, you can go for a smaller compression which will work faster or you can go for maximum compression which has the tradeoff of taking longer to run.
To get minimum compression at the fastest speed run the following command:
gzip -1 filename
To get maximum compression at the slowest speed run the following command:
gzip -9 filename
You can vary the speed and compression level by picking different numbers between 1 and 9.
Standard Zip Files
The gzip command should not be used when working with standard zip files. You can use the zip command and unzip command for handling those files.