About.com: Basic BASH ScriptingMay 28, 2000, 04:14 (0 Talkback[s])
"This article is dedicated to explaining more about the flow control and internal mechanisms useful in producing shell programs. ...Linux shell programming [is] arguably one of the biggest strengths of Linux, since it can be incorporated into most any kind of task one might want to achieve, from network management to keeping a checkbook balanced."
"It's been a long time (over two years) since our feature called Basic BASH for Beginners gave a brief introduction to using the Linux shell. This issue picks up where that issue left off; if you're not familiar with basic use of the shell, please take the time to learn the basics before proceeding with this article."
"One of the most important aspects of flow control is the use of boolean logic in making decisions about where flow will progress next. As is the case in the 'C' language, shell scripting evaluates comparisons to a numeric value (0 or 1), and programs which produce numeric "output" in the form of an exit error level (similar in this case to a function return value) can be used in place of comparison operators."