Paul Graves <paulgraves@hotmail.com> wrote:

> I keep finding Apple II software with a .shk extension.  It appears to
> be a "ShrinkIt" file -- some sort of compressed file format.

ShrinkIt (.shk) is the standard LZW compression format used on the Apple
II.  It is similar in concept to compressed file formats like Zip and
StuffIt, i.e.  it is an archive format supporting multiple files, rather
than a single file compression format like UNIX compress or gzip.  The
.shk file format isn't compatible with any of the other archive formats.

The original program ("ShrinkIt") was written by Andy Nicholas, and was
freeware.  He published the file format specification, so that others
could implement it as well.

The ShrinkIt program requires a 128K IIe (probably an enhanced IIe at
that) or a later machine.  It supports both compressing and expanding
archives, and has a variety of other file management tools.

Andy also wrote simpler 40-column versions that worked on an Apple II+,
with separate programs for compressing and expanding (IIPlus.ShrinkIt
and IIPlus.Unshrink).

At a later stage, he wrote a IIgs native version (ShrinkIt.GS or GSHK),
which requires IIgs System 5.0.4 or later.

> How can I decompress it?

The best method is to do it on an Apple II with ShrinkIt, or one of its
variants (IIPlus.Unshrink or ShrinkIt.GS).  If the file is specific to
the IIgs, it must be extracted using the IIgs version of ShrinkIt.

There is also a commercial Mac application whose name I forget ("Shrink
II" perhaps?).  I don't know if it is still available.  It was sold by
EGO Systems (publishers of the GS+ magazine).  I bought it but found it
somewhat unreliable and didn't use it very much.

Another option is the cross-platform public domain software called NuLib
(by Andy McFadden, if I remember right).  The main problem with using
NuLib is that you will lose the file system metadata (particularly the
file type and auxiliary type), which may cause problems if you copy the
extracted files to an Apple II and expect them to work.  You will also
lose the resource fork for any IIgs-specific file, which is likely to
render the file useless.

> I found a .sea file which appeared to be the ShrinkIt program, but I
> couldn't get that to self-extract.  Are these Unix or Mac formats or
> something?  Is there anyway to decompress these on a PC?

The usual method of "bootstrap loading" ShrinkIt onto an Apple II is to
start with a small version like IIPlus.Unshrink which is distributed as
an executable text file, or is distributed uncompressed in Binary II or
BinSCII format (assuming you already have a Binary II or BinSCII
decoder, either of which can be implemented in Applesoft BASIC and are
able to be distributed as an executable text file).

Once you have IIPlus.Unshrink, you can use it to extract the full
version of ShrinkIt, which was typically distributed as a .shk file.

The IIgs version (GSHK or ShrinkIt.GS) cannot be extracted with the
8-bit version of ShrinkIt, because it contains a resource fork.  The
usual method of distributing this is as a IIgs self-extracting archive,
transferred in a form which preserves the Apple II file type (Binary II
or BinSCII).  Once you had a version of ShrinkIt.GS, you could use it to
extract later versions which could be distributed in .shk format
(avoiding the overhead of the self extraction code, and simplifying file
type issues).

-- 
David Empson
dempson@actrix.gen.nz