Programming

Autoconf Tutorial
Introduction to programming using GNU's autoconf system. Autoconf simplifies the porting process and provides a consistent build interface for system administrators.
http://www.galassi.org/mark/mydocs/autoconf_tutorial_toc.html

IP Filter
TCP/IP Packet Filtering package
http://coombs.anu.edu.au/~avalon/

Serial Programming Guide for POSIX Operating Systems
Programming serial ports in Unix.
http://www.easysw.com/~mike/serial/

UNIX and Programming Section
Tutorials and manuals for Java and PHP.
http://www.softlab.ece.ntua.gr/facilities/documentation/unix/

Unix programming resources and examples
Annotated source code examples for most Unix system and library calls. Plus working source code examples of some classic algorithms.
http://www.yendor.com/programming/

Wildcard Pattern Matching
C routine to check whether a string matches a unix wildcard. '*', '?', sets of characters, and negated sets of characters are supported.
http://user.cs.tu-berlin.de/~schintke/references/wildcards/index.html