Accoring to Damian Conway there is a linear relationship between the length of a piece of code and the munber of bugs it will have and that shell script is shorter...

A better reference for this can be found in Code Complete, chapter 21, "How Program Size Affects Construction", page 523, from a study done in 1977 (Jones, T. Capers. 1977. Program Quality and Programmer Productivity. IBM Technical Report TR 02.764, January, 42-78.).

In short:

Project Size in Lines of Code	Error Density in Errors per 1K lines of code
< 2K	0 - 25
2K - 16K	0 - 40
16K - 64K	0.5 - 50
64K - 512K	2 - 70
> 512K	4 - 100

Page 610 (in Chapter 25, "Unit Testing") cites "15 to 50 errors per 1000 lines of code for delivered software" as "industry average experience".

Note however that this data is very old, and new methods for software construction may give better results. Also, some organizations, most notably NASA projects, have achieved much, much better error rates, mostly by introducing rigorous testing and code review schemes. Also note the enormous variance in the data above.

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