Listing 15.1: OS X includes several shells; here we see that sh and tcsh are located in /bin. If we look for other shells in /bin, we find that there are actually five. Finally, we see that sh is really bash, and that csh is actually the same as tcsh.
Listing 15.2: Local variables in tcsh
Listing 15.3: Environment variables in tcsh
Listing 15.4: Using alias and unalias (the first line produces no response because no aliases exist yet)
Listing 15.5: Types of Files in /usr/bin
Listing 15.6: How does OS X finish starting up? It runs an sh script!
Listing 15.7: Sample pipelines
Listing 15.8: Using input/output redirection
Listing 15.9: Using backticks to feed filenames from the which command's standard output to another command as arguments
Listing 15.10: Output from tcpdump when visiting http://www.reppep.com/~pepper/ in a web browser; the right column shows requests to and responses from the server.