This is the source used for Slackware 3.4.0.

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.

Most of these packages now have scripts that untar, patch, and compile the
source automatically.

Have fun!

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