With the enormous amount of enterprise data that is created and stored, there is a pressing need to conserve disk space and optimize data transfer time. There are various tools, utilities, and commands that are used for file compression. Some of the commonly used commands are:
– The compress command
– The gzip command
– The zip command
The compress Command
When compressing a file, the compress command replaces the original file with a new file that has a .Z extension.
$ compress [ -v ] filename
The ownership and modification time of the original file remain intact, but the content of the file changes. The amount of compression depends on the type of file you compress. Typically, compression reduces a text file by 50 to 60 percent.
Compressing a File: compress Command
The following example shows you how to compress a file called test.tar.
# compress -v test.tar test.tar: -- replaced with test.tar.Z Compression: 96.35%
# ls -lrt test.tar.Z -rw-r--r--. 1 root root 373 Dec 7 19:31 test.tar.Z
– The -v (verbose) option provides information about the percentage of reduction or expansion of each file.
– The compressed file, test.tar.Z, replaces the test.tar file.
Viewing a Compressed File: zcat Command
The zcat command prints the uncompressed form of a compressed file to the standard output.
$ zcat filename
To view the content of the data.txt.Z compressed file, enter the following command:
# zcat data.txt.Z northwest NW Joel Craig 10 western WE Sharon Kelly 40 southwest SW Chris Foster 33 northeast NE TJ Nichols 67 north NO Val Shultz 91 central CT Sheri Watson 44
The zcat filename command is functionally identical to the uncompress -c filename command. For example the to view the content of the compressed file data.txt.Z, we can also use the command shown below.
uncompress -c data.txt.Z
Uncompressing a File: uncompress Command
The uncompress command restores a compressed file to an uncompressed state.
$ uncompress options filename
To uncompress the test.tar.Z file and restore it to the test.tar file, enter the following command:
# uncompress -v test.tar.Z test.tar.Z: -- replaced with test.tar
The -v option displays additional messages about the action being performed.
You can use the uncompress command with the -c option to send the content of a compressed file to the stdout, the screen, without changing the compressed .Z file. Otherwise, you can use the pipe (|) character to send the output of the uncompress command to another program.
You can use the tar command to list the content of the file that the uncompress command is reading.
# uncompress -c test.tar.Z | tar tvf - -rw-r--r-- root/root 31 2017-12-02 07:02 test -rw-r--r-- root/root 19 2017-12-02 07:04 test1 -rw-r--r-- root/root 20 2017-12-02 07:04 test2
The dash (-) at the end of the command line indicates that the tar command reads the data from the piped output of the uncompress command rather than a tar file or a disk.
Compressing a File: gzip Command
Alternatively, you can also use the gzip command to compress files.
$ gzip [ -v ] filenames
The gzip command performs the same function as the compress command, but the gzip command generally produces smaller files. For example, to compress a set of files, file1, file2, file3, and file4, enter the following command:
$ gzip file1 file2 file3 file4 $ ls *.gz file1.gz file2.gz file3.gz file4.gz
The compressed files have a .gz extension.
Viewing a Compressed File: gzcat Command
The gzcat command displays files that were compressed with either the gzip or compress commands.
$ gzcat filename
To view the data.txt.gz file, use the following command:
# gzcat data.txt.gz northwest NW Joel Craig 10 western WE Sharon Kelly 40 southwest SW Chris Foster 33 northeast NE TJ Nichols 67 north NO Val Shultz 91 central CT Sheri Watson 44
Uncompressing a File: gunzip Command
The gunzip command uncompresses a file that has been compressed with the gzip command.
$ gunzip filename
To uncompress the file1.gz file, use the following command:
$ gunzip file1.gz
Compressing and Archiving Multiple Files: zip Command
The zip command compresses and archives multiple files into a single file in one go.
$ zip target_filename source_filenames
To compress test1 and test2 into the test.zip archive file, enter the following command:
# zip test.zip test1 test2 adding: test1 (deflated 5%) adding: test2 (stored 0%)
# ls -l test.zip -rw-r--r--. 1 root root 336 Dec 8 05:32 test.zip
By default, the zip command adds the .zip extension to the compressed archive file if you do not assign a new file name with an extension.
Viewing and Uncompressing Archive Files: unzip Command
The unzip command is used for listing the files and also for extracting the content of a compressed .zip file.
$ unzip zipfile
To uncompress the file.zip archive file, use the following command:
$ unzip file.zip