Simulated Bourne Shell Functions and Aliases (Unix Power Tools, 3rd Edition) 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: test Section 35.26 cps( ) { if test ! -s "$2" then cp "$1" "$2" else echo "cps: cannot copy $1: $2 exists" fi } If you use the same cps twice, the first time you'll make bfile. The second time you try, you see the error: $ cps afile bfile ... $ cps afile bfile cps: cannot copy afile: bfile exists Here's the same cps -- stored in a shell variable instead of a function: cps=' if test ! -s "$2" then cp "$1" "$2" else echo "cps: cannot copy $1: $2 exists" fi ' Because this fake function uses shell parameters, you have to add an extra step: setting the parameters. Simpler functions are easier to use: set Section 35.25 $ set afile bfile $ eval "$cps" ... $ eval "$cps" cps: cannot copy afile: bfile exists -- JP 29.13. Propagating Shell Functions30. The Use of History Copyright © 2003 O'Reilly & Associates. All rights reserved.