29.14. Simulated Bourne Shell Functions and Aliases

Until System V Release 2 (circa 1984), the Bourne shell had no way for users to set up their own built-in commands. If you have a Bourne shell with no functions (Section 29.11) or aliases (Section 29.2) and haven't yet turned the host machine into a wet bar, CD/DVD storage case, or some other pragmatic but fun use for a 30-year-old computer, you can do a lot of the same things with shell variables and the eval (Section 27.8) command.

Let's look at an example. First, here's a shell function named cps (copy safely). If the destination file exists and isn't empty, the function prints an error message instead of copying: