XZ Utils on DOS
===============
DOS-specific filename handling
xz detects at runtime if long filename (LFN) support is
available and will use it by default. It can be disabled by
setting an environment variable:
set lfn=n
When xz is in LFN mode, it behaves pretty much the same as it
does on other operating systems. Examples:
xz foo.tar -> foo.tar.xz
xz -d foo.tar.xz -> foo.tar
xz -F lzma foo.tar -> foo.tar.lzma
xz -d foo.tar.lzma -> foo.tar
When LFN support isn't available or it is disabled with LFN=n
environment setting, xz works in short filename (SFN) mode. This
affects filename suffix handling when compressing.
When compressing to the .xz format in SFN mode:
- Files without an extension get .xz just like on LFN systems.
- *.tar files become *.txz (shorthand for *.tar.xz). *.txz
is recognized by xz on all supported operating systems.
(Try to avoid confusing this with gzipped .txt files.)
- Files with 1-3 character extension have their extension modified
so that the last character is a dash ("-"). If the extension
is already three characters, the last character is lost. The
resulting *.?- or *.??- filename is recognized in LFN mode, but
it isn't recognized by xz on other operating systems.
Examples:
xz foo -> foo.xz | xz -d foo.xz -> foo
xz foo.tar -> foo.txz | xz -d foo.txz -> foo.tar
xz foo.c -> foo.c- | xz -d foo.c- -> foo.c
xz read.me -> read.me- | xz -d read.me- -> read.me
xz foo.txt -> foo.tx- | xz -d foo.tx- -> foo.tx !
Note that in the last example above, the third character of the
filename extension is lost.
When compressing to the legacy .lzma format in SFN mode:
- *.tar files become *.tlz (shorthand for *.tar.lzma). *.tlz
is recognized by xz on all supported operating systems.
- Other files become *.lzm. The original filename extension
is lost. *.lzm is recognized also in LFN mode, but it is not
recognized by xz on other operating systems.
Examples:
xz -F lzma foo -> foo.lzm | xz -d foo.lzm -> foo
xz -F lzma foo.tar -> foo.tlz | xz -d foo.tlz -> foo.tar
xz -F lzma foo.c -> foo.lzm | xz -d foo.lzm -> foo !
xz -F lzma read.me -> read.lzm | xz -d read.lzm -> read !
xz -F lzma foo.txt -> foo.lzm | xz -d foo.lzm -> foo !
When compressing with a custom suffix (-S .SUF, --suffix=.SUF) to
any file format:
- If the suffix begins with a dot, the filename extension is
replaced with the new suffix. The original extension is lost.
- If the suffix doesn't begin with a dot and the filename has no
extension and the filename given on the command line doesn't
have a dot at the end, the custom suffix is appended just like
on LFN systems.
- If the suffix doesn't begin with a dot and the filename has
an extension (or an extension-less filename is given with a dot
at the end), the last 1-3 characters of the filename extension
may get overwritten to fit the given custom suffix.
Examples:
xz -S x foo -> foox | xz -dS x foox -> foo
xz -S x foo. -> foo.x | xz -dS x foo.x -> foo
xz -S .x foo -> foo.x | xz -dS .x foo.x -> foo
xz -S .x foo. -> foo.x | xz -dS .x foo.x -> foo
xz -S x.y foo -> foox.y | xz -dS x.y foox.y -> foo
xz -S .a foo.c -> foo.a | xz -dS .a foo.a -> foo !
xz -S a foo.c -> foo.ca | xz -dS a foo.ca -> foo.c
xz -S ab foo.c -> foo.cab | xz -dS ab foo.cab -> foo.c
xz -S ab read.me -> read.mab | xz -dS ab read.mab -> read.m !
xz -S ab foo.txt -> foo.tab | xz -dS ab foo.tab -> foo.t !
xz -S abc foo.txt -> foo.abc | xz -dS abc foo.abc -> foo !
When decompressing, the suffix handling in SFN mode is the same as
in LFN mode. The DOS-specific filenames *.lzm, *.?-, and *.??- are
recognized also in LFN mode.
xz handles certain uncommon situations safely:
- If the generated output filename refers to the same file as
the input file, xz detects this and refuses to compress or
decompress the input file even if --force is used. This can
happen when giving an overlong filename in SFN mode. E.g.
"xz -S x foo.texinfo" would try to write to foo.tex which on
SFN system is the same file as foo.texinfo.
- If the generated output filename is a special file like "con"
or "prn", xz detects this and refuses to compress or decompress
the input file even if --force is used.
Bugs
xz doesn't necessarily work in Dosbox. It should work in DOSEMU.
Pressing Ctrl-c or Ctrl-Break won't remove the incomplete target file
when running under Windows XP Command Prompt (something goes wrong
with SIGINT handling). It works correctly under Windows 95/98/98SE/ME.