On Monday 17 June 2013 16:37:06 Rick "Zero_Chaos" Farina wrote:
> On 06/17/2013 04:19 PM, Diego Elio Pettenò wrote:
> > On 17/06/2013 17:54, Rick "Zero_Chaos" Farina wrote:
> >> I make all my files with "tar cJf"
> >> 
> >> zero@ozzie ~ % file /usr/portage/distfiles/gr-osmosdr-0.0.2.tar.xz
> >> /usr/portage/distfiles/gr-osmosdr-0.0.2.tar.xz: XZ compressed data
> > 
> > cJ with _current_ tar will generate XZ
> > cJ with _past_ tar could generate lzma
> > xJ with _current_ tar will extract both XZ and lzma
> > zJ with _past_ tar will only extract lzma
> 
> tar for the last several years properly and automatically detects the
> format of the input using just 'x'.  This is true for gnu and bsd tar
> which should cover all of gentoo.

and that relies on the magic being in the output format which, as we pointed 
out, wasn't the case.  it's one of the reasons why the XZ format came to be.

build lzma-utils and compress some files and see how well tar & file handle it:
	http://tukaani.org/lzma/
-mike