What are .xsh files? How to see its contents?

Question

The synology ipkg installer bootstraps with a file, with name ending .xsh. How can I see what is inside such file?

Answer 1

These are "self-extracting" archives; the first one I found has this code at the top:

#!/bin/sh
echo "Optware Bootstrap for syno-i686."
echo "Extracting archive... please wait"
dd if=$0 bs=205 skip=1 | tar xzv
cd bootstrap && sh bootstrap.sh && cd .. && rm -r bootstrap
exec /bin/sh --login

... which indicates that it's basically a (large) shell script, where the interesting part is the dd ... | tar xzv line; the other lines are specific to that particular package.

The dd command reads from $0 -- the current file -- skipping past the correct number of bytes; that output is then sent to tar who's expecting a compressed archive. A compressed tar file has been inserted exactly at that position in the xsh file.

To view/extract it yourself, just follow the same instructions -- which will vary per xsh file! -- namely:

$ dd if=syno-i686-bootstrap_1.2-7_i686.xsh bs=205 skip=1 > bootstrap.tgz
$ gunzip bootstrap.tgz  ## for example
$ tar tf bootstrap.tar  ## for example
bootstrap/
bootstrap/bootstrap.sh
bootstrap/ipkg-opt.ipk
bootstrap/ipkg.sh
...

As a slightly more general rule for extracting the archives, you could look for that dd signature, telling grep that it's OK to output the match in this "binary" file:

$ grep -a '^dd if=$0' syno-i686-bootstrap_1.2-7_i686.xsh 
dd if=$0 bs=205 skip=1 | tar xzv

... which you can then copy/paste to view or extract the contents as you like. You may also be interested in the other commands being executed; view those similarly, with -- again, specific to this example:

$ dd if=syno-i686-bootstrap_1.2-7_i686.xsh bs=205 count=1
#!/bin/sh
echo "Optware Bootstrap for syno-i686."
echo "Extracting archive... please wait"
dd if=$0 bs=205 skip=1 | tar xzv
cd bootstrap && sh bootstrap.sh && cd .. && rm -r bootstrap
exec /bin/sh --login
1+0 records in
1+0 records out
205 bytes (205 B) copied, 4.7985e-05 s, 4.3 MB/s