Extracting the contents of a folder in a CPIO archive to another folder

Refractor · 05-29-2012, 02:49 PM

Greetings,
since my English is not that good and maybe the title is a bit(lot) confusing, I'll give an example:
I have a CPIO archive with the following structure:

Code:

/folder1
|- file1
|- file2
/folder2
|-/subfolder1
|-|-file3
|-|-file4
|-/subfolder2
|-|-file5

Is there a way to extract only the contents of a folder with CPIO (either GNU or BSD) without extracting the folder itself?
when I try cpio -idv folder2/* < archive.cpio
I get a folder2 and all files in it, but what I need is the contents of folder2 without creating the parent folder itself.

I hope that cleared it. Thanks in advance!

colucix · 05-29-2012, 04:54 PM

cpio cannot do that, unless you use the -r option to rename files interactively. It could be very annoying, anyway. Use pax instead that works similarly to cpio but in addition has an option to rename the archived files based on ed regexp. Here we go:

1. to list the content of the archive use pax without options

Code:

$ pax < archive.cpio
folder1
folder1/file1
folder1/file2
folder2
folder2/subfolder2
folder2/subfolder2/file5
folder2/subfolder1
folder2/subfolder1/file4
folder2/subfolder1/file3

this is just to show the archive I previously created in order to resemble your example. The output is similar to what you can obtain by running cpio -t < archive.cpo.

2. to list a partial content based on a pattern:

Code:

$ pax < archive.cpio folder2/*
folder2/subfolder2
folder2/subfolder2/file5
folder2/subfolder1
folder2/subfolder1/file4
folder2/subfolder1/file3

this is similar to cpio -t < archive.cpio folder2/*.

3. extract the content of folder2 in the current working directory (and this actually answers your question):

Code:

$ pax -r -s '/\<folder2\>\///' < archive.cpio folder2/*
$ ls
archive.cpio  subfolder1  subfolder2
$ ls -R
.:
archive.cpio  subfolder1  subfolder2

./subfolder1:
file3  file4

./subfolder2:
file5

and the trick is done!

Refractor · 05-30-2012, 03:32 PM

Thanks a bunch, was wondering for ages how to get it working without scripts to move folders around!

colucix · 05-30-2012, 03:59 PM

You're welcome!

Indeed, the -s option of pax is very powerful, since you can really extract files and sub-directories wherever you want. Just substitute the unwanted path with another and pax will create any non-existent directory tree. In addition, changing the / delimiter with another character, let you easily manage slashes in long paths, e.g.

Code:

pax -r -s ':\<folder2\>/:deep/path/where/i/want/to/extract/my/files/:' < archive.cpio folder2/*

The only caveat is the regexp that must be carefully designed to match the portion (and only that portion) of the original path we want to change or remove.

ruario · 07-10-2012, 06:12 PM

Or you could use bsdtar, it also supports substitution with -s and can read and output in cpio format. Additionally many distros have it preinstalled as part of the libarchive package (e.g. Slackware, Arch, etc.).

Additionally bsdtar (libarchive) is more actively maintained than most of the pax implementations floating around.