advantages of cpio command? Post: 302226121

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Top Forums UNIX for Dummies Questions & Answers advantages of cpio command? Post 302226121 by buffoonix on Monday 18th of August 2008 09:53:21 AM

08-18-2008

Registered User

As era correctly assumed, tar was initially a tool for creating and extracting tape archives, hence its name.
For instance the manpage for tar on HP-UX still mentions this

Quote:

tar(1) tar(1)

NAME
tar - tape file archiver

And for those historic kind of uses it goes on, informing that indeed the -f option can be omitted,
where it defaults to the first non-rewinding tape device special file

Quote:

DESCRIPTION
The tar command saves and restores archives of files on a magnetic
tape, a flexible disk, or a regular file. The default archive file is
/dev/rmt/0m. See the -f option below. Its actions are controlled by
the key argument.

Of course, on Linux distros bundled with the GNU tar this does not apply
because I think that Linux wasn't targeted in the first place at users who can afford
expensive tape drives and media.

Both tools have their pros and cons.
Of course, we must not confuse the myriad of features the GNU tar offers nowadays
with those spartan tar implementations that you would find on most commercial Unices.

Historically, tar didn't back up special files.
Also you couldn't easily exclude files from being captured in the archive
as well as not restrict the recursion to filesystem boundaries.
(GNU tar today has all sorts of options that let you do this)
On the other hand it is easy to append files to existing tar archives which you can't with cpio.
Another drawback of cpio is that it usually only is useful in combination with find,
which makes two stat() syscalls for each file (albeit the second is read from the buffer cache).
One big strength of cpio draws from the abundance of filter criteria,
which on the other hand can become quite daunting to the average user.
Think of the arcane -prune logic with lots of quoting noise for parens if you want to exclude certain dirs.

But to the remedy came a tool which sadly his often hardly known.
It kind of took its name from the former rivalry of the two, tar vs. cpio.
As pax is the Latin word for peace, so it is aptly named.
pax lets you do much more than a mere tar (e.g. in situ renaming of target paths or stripping) while it maintains tar's ease of use.
pax should really be given more attention.

buffoonix

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git-tar-tree

GIT-TAR-TREE(1) 						    Git Manual							   GIT-TAR-TREE(1)

NAME

       git-tar-tree - Create a tar archive of the files in the named tree object

SYNOPSIS

       git tar-tree [--remote=<repo>] <tree-ish> [ <base> ]

DESCRIPTION

       THIS COMMAND IS DEPRECATED. Use git archive with --format=tar option instead (and move the <base> argument to --prefix=base/).

       Creates a tar archive containing the tree structure for the named tree. When <base> is specified it is added as a leading path to the files
       in the generated tar archive.

       git tar-tree behaves differently when given a tree ID versus when given a commit ID or tag ID. In the first case the current time is used
       as modification time of each file in the archive. In the latter case the commit time as recorded in the referenced commit object is used
       instead. Additionally the commit ID is stored in a global extended pax header. It can be extracted using git get-tar-commit-id.

OPTIONS

       <tree-ish>
	   The tree or commit to produce tar archive for. If it is the object name of a commit object.

       <base>
	   Leading path to the files in the resulting tar archive.

       --remote=<repo>
	   Instead of making a tar archive from local repository, retrieve a tar archive from a remote repository.

CONFIGURATION

       tar.umask
	   This variable can be used to restrict the permission bits of tar archive entries. The default is 0002, which turns off the world write
	   bit. The special value "user" indicates that the archiving user's umask will be used instead. See umask(2) for details.

EXAMPLES

       git tar-tree HEAD junk | (cd /var/tmp/ && tar xf -)
	   Create a tar archive that contains the contents of the latest commit on the current branch, and extracts it in /var/tmp/junk directory.

       git tar-tree v1.4.0 git-1.4.0 | gzip >git-1.4.0.tar.gz
	   Create a tarball for v1.4.0 release.

       git tar-tree v1.4.0^{tree} git-1.4.0 | gzip >git-1.4.0.tar.gz
	   Create a tarball for v1.4.0 release, but without a global extended pax header.

       git tar-tree --remote=example.com:git.git v1.4.0 >git-1.4.0.tar
	   Get a tarball v1.4.0 from example.com.

       git tar-tree HEAD:Documentation/ git-docs > git-1.4.0-docs.tar
	   Put everything in the current head's Documentation/ directory into git-1.4.0-docs.tar, with the prefix git-docs/.

AUTHOR

       Written by Rene Scharfe.

DOCUMENTATION

       Documentation by David Greaves, Junio C Hamano and the git-list <git@vger.kernel.org[1]>.

GIT

       Part of the git(1) suite

NOTES

	1. git@vger.kernel.org
	   mailto:git@vger.kernel.org

Git 1.7.1							    07/05/2010							   GIT-TAR-TREE(1)