Nobody really knows what the Bourne shell's grammar is. Even examination of the source code is little help.
Shared libraries are the work of the devil, the one true sign that the apocalypse is at hand.
Whenever possible, steal code.
With diligence it is possible to make anything run slowly.
The first step in fixing a broken program is getting it to fail repeatably [on the simplest example possible].
Don't use hands to do things that can be efficiently done by the computer.
How many seconds are there in a year? If I tell you there are 3.155 x 10^7, you won't even try to remember it. On the other hand, who could forget that, to within half a percent, pi seconds is a nanocentury.