Re: A system administration use case for git

["Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>]

Hello Jon,

On Wed, Apr 22, 2009 at 06:33:12PM +1000, Jon Seymour wrote:
> * calculate the git hashes of the tree (without making copies of the
> files in the tree)
You can hand-craft a tree object:

	for f in $filelist; do
		printf "100644 %s\x00" $f;

		git hash-object $f |
			perl -n -e 'chomp; for $c (split(/(.{2})/)) { printf("%c", hex($c)) if $c }';
	done |
		git hash-object -t tree --stdin


You get some extra points for directories that include subdirs :-)

There is a problem though, I think it has to do with the order of the
files in the tree object.  Here is a real-life example from the Linux
kernel (I choosed the usr subdirectory, because it's small and doesn't
contain subdirs):

	ukleinek@cepheus:~/gsrc/linux-2.6/usr$ for f in .gitignore Kconfig Makefile gen_init_cpio.c initramfs_data.S initramfs_data.bz2.S initramfs_data.gz.S initramfs_data.lzma.S; do printf "100644 %s\x00" $f; git hash-object $f | perl -n -e 'chomp; for $c (split(/(.{2})/)) { printf("%c", hex($c)) if $c }'; done | git hash-object -t tree --stdin
	64f2ca854bc19fd29479b198be11beba56a26b1e

	ukleinek@cepheus:~/gsrc/linux-2.6/usr$ git rev-parse HEAD:usr
	64f2ca854bc19fd29479b198be11beba56a26b1e

There is a practical problem though:  The filelist has to be sorted in a
way that is not provided by ls, so:

	ukleinek@cepheus:~/gsrc/linux-2.6/usr$ for f in $(ls -A); do printf "100644 %s\x00" $f; git hash-object $f | perl -n -e 'chomp; for $c (split(/(.{2})/)) { printf("%c", hex($c)) if $c }'; done | git hash-object -t tree -w --stdin
	a0a6efb3f1de956badc7607c7d372cc325a18846

	ukleinek@cepheus:~/gsrc/linux-2.6/usr$ git ls-tree a0a6efb3f1de956badc7607c7d372cc325a18846 | wc -l
	0

doesn't work :-/

This would make a nice plumbing:

	git hash-tree $directory

Best regards
Uwe

-- 
Pengutronix e.K.                              | Uwe Kleine-König            |
Industrial Linux Solutions                    | http://www.pengutronix.de/  |