Compression and Archiving

File Compression and Archiving

• An archive file is a collection of files and directories that are stored in one file. The archive file is not compressed — it uses the same amount of disk space as all the individual files and directories combined.

• A compressed file is a collection of files and directories that are stored in one file and stored in a way that uses less disk space than all the individual files and directories combined. If you do not have enough disk space on your computer, you can compress files that you do not use very often or files that you want to save but do not use anymore. You can even create an archive file and then compress it to save disk space.

Note : An archive file is not compressed, but a compressed file can be an archive file.

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Compression Only

Compression Tool	File Extension	Uncompression Tool	Example
gzip	.gz	gunzip	Compress : gzip fileName Decompress gunzip fileName.gz
bzip2	.bz2	bunzip2	Compress : bzip2 fileName Decompress bunzip2 fileName.bz2

• Some of the options used with the gzip/bzip2 are:

  • -c, --stdout — Write output to standard output and keep the original file.

  • -d, --decompress — Decompress. This causes gzip to act like gunzip.

  • -f, --force — Force compression even if a compressed version of the original file already exists.

  • -l, --list — List compression statistics for each file compressed.

  • -r, --recursive — Recursively compress files contained within a directory.

    available for gzip only.

  • -t, --test — Test the integrity of a compressed file.

  • -1 .. -9 — Set ammount of compression. range from 1 (fastest, least compression) to 9 (slowest, most compression). Default value is 6.

  • -1, --fast — Compress faster.

  • -9, --best — Compress better.

  • -v — Tell the program to be verbose and let us see what it's doing.

• You can compress multiple files :

  • gzip file1 file2 file3 ⇾ Output : file1.gz file2.gz file3.gz
  • bzip2 file1 file2 file3 ⇾ Output : file1.bz2 file2.bz2 file3.bz2

  gzip and bzip2 can't add multiple files into one archive.

• You can decompress multiple files :

  • gunzip file1.gz file2.gz file3.gz
  • bunzip2 file1.bz2 file2.bz2 file3.bz2

  -k, --keep — Don't delete input files.

• You can decompress a file to stdout :

  • zcat file1.gz — is identical to gunzip -c file1.gz

    On some systems, zcat may be installed as gzcat.

  • bzcat file1.bz2 — is identical to bunzip2 -c file1.bz2

• You can decompress a file and pipe its content to less :

  • zless file1.gz — is identical to gunzip -c file1.gz | less
  • bless file1.bz2 — is identical to bunzip2 -c file1.bz2 | less

You can compress multiple files and directories :

• bzip2 file1 file2 file3 /usr/work/school/*

• gzip -r file1 file2 file3 /usr/work/school ⇾ Output : file1.gz file2.gz file3.gz /usr/work/school/AllFiles.gz

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Archiving and Compression zip

Tool	File Extension	Decompression Tool	Example
zip	.zip	unzip	Compress : zip file.zip fileName Decompress unzip fileName.zip

• To compress multiple files : zip files.zip file1 file2 file3 ⇾ Output : files.zip

  .zip can be omitted.

• To decompress multiple files : unzip '*.zip'

• To list compression statistics for a zip file contents (short format) : unzip -l files.zip

  add -v for long format.

• To decompress a specific file : unzip -j files.zip path/to/file -> Output : file

• To decompress a specific file to stdout : unzip -p files.zip file1

  -p — extract file to stdout.

• To decompress a file to stdout: unzip -c file1.zip

• To compress multiple files and directories : zip -r filename.zip file1 file2 file3 /usr/work/school

  • The above command compresses file1, file2, file3, and the contents of the /usr/work/school directory and places them in a file named filename.zip.

• To decompress a specific directory : unzip files.zip 'path/to/dir/**/*' 'path/to/dir/*'

  • Extracts dir to the current directory.

If you need to transfer files between Linux and other operating system such as MS Windows, you should use zip because it is more commonly used on those other operating systems.

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Creating Archives with tar

• A tar file is a collection of several files and/or directories in one file. When you create an archive using tar, it will have a .tar extension.

• tar command syntax : tar -mode[options] pathname...

  - can be omitted : tar mode[options] pathname...

• tar modes:

  • -c — create a new archive.

  • -x — extract files from an archive.

  • -r — append specified pathanmes to the end of an archive.

  • -t, --list — list the contents of an archive.

• Some of the options used with the tar are:

  • -f — when used with the

    • -c mode, use the filename specified for the creation of the tar file.
    • -x mode, unarchive the specified file.
    • -t mode, list the contents of the specified archive.
    • -r mode, append specified pathanmes to the end of the specified archive.

  • -v — tell the program to be verbose and let us see what it's doing.

  • -t — show the list of files in the tar file.

  • -z — compress the tar file with gzip.

  • -j — compress the tar file with bzip2.

  • -O, --to-stdout — extract files to stdout.

• To create a tar file : tar -cvf filename.tar files/directories

  • tar -cvf filename.tar /home/mine/work /home/mine/school
    • The above command places all the files in the work and the school subdirectories of /home/mine in a new file called filename.tar in the current directory.

• To list the contents of a tar file : tar -tvf filename.tar or tar -tf filename.tar

• To extract the contents of a tar file : tar -xvf filename.tar

• To extract a specific file from a tar file : tar -xvf filename.tar path/to/file

• To extract a specific directory from a tar file : tar -xvf filename.tar path/to/directory

Remember, the tar command does not compress the files by default.

• To create a tarred and gzipped compressed file, use the -z option: tar -czvf filename.tgz files/directories

  • tar files compressed with gzip are conventionally given the extension .tgz or tar.gz.

  • This command creates the archive file filename.tar and then compresses it as the file filename.tgz. If you uncompress the filename.tgz file with the gunzip command, the filename.tgz file is removed and replaced with filename.tar.

• To extract a gzip tar archive : tar xzvf filename.tar.gz

• To extract a specific file from a gzip tar archive : tar -xvf filename.tgz path/to/file

• To extract a specific directory from a gzip tar archive : tar -xvf filename.tgz path/to/directory

• To create a tarred and bzipped compressed file, use the -j option : tar -cjvf filename.tbz files/directories

  • tar files compressed with bzip2 are conventionally given the extension .tbz.

  • This command creates an archive file and then compresses it as the file filename.tbz. If you uncompress the filename.tbz file with the bunzip2 command, the filename.tbz file is removed and replaced with filename.tar.

• To extract a bzip2 tar archive : tar xjvf filename.tar.tbz

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↗ List of archive formats