This is the source used for Slackware 3.5.0.

To look for a particular bit of source (let's say for 'cp'), first you
would look for the full path:

fuzzy:~# which cp
/bin/cp

Then, you grep for the package it came from. Note that the leading '/'
is removed:

fuzzy:~# grep bin/cp /var/adm/packages/*
/var/adm/packages/bin:bin/cp
/var/adm/packages/cpio:bin/cpio
/var/adm/packages/perl:usr/bin/cppstdin

From this, you can see that 'cp' came from the bin.tgz package. The source 
will be found in a corresponding subdirectory. In this case, that would be
./a/bin.  Don't be fooled into thinking that the _bin.tar.gz in this directory
is the package with the source code -- anything starting with '_' is just a
framework package full of empty files with the correct permissions and 
ownerships for the completed package to use.

Most of these packages now have scripts that untar, patch, and compile the
source automatically.  These are the 'SlackBuild' scripts.  Moving back to
the example above, you can figure out which package the bin/cp source came
from by examining the SlackBuild script.

Have fun!

---
Patrick J. Volkerding
volkerdi@ftp.cdrom.com