You might also want to read some documentation about what the shell you use is actually doing with your command string before executing the command it contains. There is common ground here, but of course the different shells do different things with your command string, so talking of "the shell" is a bit of a simplification here (and that's just talking about Unix/Linux shells, not to mention all this bizarre other stuff).

For a quick and wordy start, why not just read through "info bash", or if you like books, try Learning the bash shell, which contains a nice one-page summary of the process that bash goes through in parsing and evaluating your input. Unix Power Tools also has some nice short articles on what happens when the shell "does" your command string.

Christian Lemburg
Brainbench MVP for Perl
http://www.brainbench.com