Monday, April 26, 2010

How to *.tar/ *.tar.gz/ *.tgz/ *.tar.bz2

1. Creating an archive using tar command
Creating an uncompressed tar archive using option cvf
This is the basic command to create a tar archive.
$ tar cvf archive_name.tar dirname/
In the above command:
c – create a new archive
v – verbosely list files which are processed.
f – following is the archive file name
Creating a tar gzipped archive using option cvzf
The above tar cvf option, does not provide any compression. To use a gzip compression on the tar archive, use the z option as shown below.
$ tar cvzf archive_name.tar.gz dirname/
z – filter the archive through gzip
Note: .tgz is same as .tar.gz
Creating a bzipped tar archive using option cvjf
Create a bzip2 tar archive as shown below:
$ tar cvjf archive_name.tar.bz2 dirname/
j – filter the archive through bzip2
gzip vs bzip2: bzip2 takes more time to compress and decompress than gzip. bzip2 archival size is less than gzip.
Note: .tbz and .tb2 is same as .tar.bz2
Note: I like to keep the ‘cvf’ option unchanged for all archive creation, and add additional option at the end, which is easier to remember. i.e cvf for archive creation, cvzf for compressed gzip archive creation, cvjf for compressed bzip2 archive creation etc.,
2. Extracting (untar) an archive using tar command
Extract a *.tar file using option xvf
Extract a tar file using option x as shown below:
$ tar xvf archive_name.tar
x – extract files from archive
Extract a gzipped tar archive ( *.tar.gz ) using option xvzf
Use the option z for uncompressing a gzip tar archive.
$ tar xvzf archive_name.tar.gz
Extracting a bzipped tar archive ( *.tar.bz2 ) using option xvjf
Use the option j for uncompressing a bzip2 tar archive.
$ tar xvjf archive_name.tar.bz2
Note: In all the above commands v is optional, which lists the file being processed.
3. Listing an archive using tar command
View the tar archive file content without extracting using option tvf
You can view the *.tar file content before extracting as shown below.
$ tar tvf archive_name.tar
View the *.tar.gz file content without extracting using option tvzf
You can view the *.tar.gz file content before extracting as shown below.
$ tar tvzf archive_name.tar.gz
View the *.tar.bz2 file content without extracting using option tvjf
You can view the *.tar.bz2 file content before extracting as shown below.
$ tar tvjf archive_name.tar.bz2
4. Extract a single file from tar, tar.gz, tar.bz2 file
To extract a specific file from a tar archive, specify the file name at the end of the tar xvf command as shown below. The following command extracts only a specific file from a large tar file.
$ tar -xvf archive_file.tar /path/to/file
Use the relevant option z or j according to the compression method gzip or bzip2 respectively as shown below.
$ tar -xvzf archive_file.tar.gz /path/to/file

$ tar -xvjf archive_file.tar.bz2 /path/to/file
5. Extract a single directory from tar, tar.gz, tar.bz2 file
To extract a single directory (along with it’s subdirectory and files) from a tar archive, specify the directory name at the end of the tar xvf command as shown below. The following extracts only a specific directory from a large tar file.
$ tar -xvf archive_file.tar /path/to/dir/
To extract multiple directories from a tar archive, specify those individual directory names at the end of the tar xvf command as shown below.
$ tar -xvf archive_file.tar /path/to/dir1/ /path/to/dir2/
Use the relevant option z or j according to the compression method gzip or bzip2 respectively as shown below.
$ tar -xvzf archive_file.tar.gz /path/to/dir/

$ tar -xvjf archive_file.tar.bz2 /path/to/dir/
6. Extract group of files from tar, tar.gz, tar.bz2 archives using regular expression
You can specify a regex, to extract files matching a specified pattern. For example, following tar command extracts all the files with pl extension.
$ tar -xvf archive_file.tar --wildcards '*.pl'
Options explanation:
–wildcards *.pl – files with pl extension
7. Adding a file or directory to an existing archive using option -r
You can add additional files to an existing tar archive as shown below. For example, to append a file to *.tar file do the following:
$ tar rvf archive_name.tar newfile
This newfile will be added to the existing archive_name.tar. Adding a directory to the tar is also similar,
$ tar rvf archive_name.tar newdir/
Note: You cannot add file or directory to a compressed archive. If you try to do so, you will get “tar: Cannot update compressed archives” error as shown below.
$ tar -rvzf archive_name.tgz newfile
tar: Cannot update compressed archives
Try `tar --help' or `tar --usage' for more information.
8. Verify files available in tar using option -W
As part of creating a tar file, you can verify the archive file that got created using the option W as shown below.
$ tar cvfW file_name.tar dir/
If you are planning to remove a directory/file from an archive file or from the file system, you might want to verify the archive file before doing it as shown below.
$ tar tvfW file_name.tar
Verify 1/file1
1/file1: Mod time differs
1/file1: Size differs
Verify 1/file2
Verify 1/file3
If an output line starts with Verify, and there is no differs line then the file/directory is Ok. If not, you should investigate the issue.
Note: for a compressed archive file ( *.tar.gz, *.tar.bz2 ) you cannot do the verification.
Finding the difference between an archive and file system can be done even for a compressed archive. It also shows the same output as above excluding the lines with Verify.
Finding the difference between gzip archive file and file system
$ tar dfz file_name.tgz
Finding the difference between bzip2 archive file and file system
$ tar dfj file_name.tar.bz2
9. Estimate the tar archive size
The following command, estimates the tar file size ( in KB ) before you create the tar file.
$ tar -cf - /directory/to/archive/ | wc -c
20480
The following command, estimates the compressed tar file size ( in KB ) before you create the tar.gz, tar.bz2 files.
$ tar -czf - /directory/to/archive/ | wc -c
508

$ tar -cjf - /directory/to/archive/ | wc -c
428
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