Common shell script mistakes

I’ve written a few shell scripts in my time and have read many more, and I see the same issues cropping up again and again (unfortunately even in my own scripts sometimes).

While there are lots of shell programming pitfalls, at least the interpreter will tell you immediately about them. The mistakes I describe below, generally mean that your script will run fine now, but if the data changes or you move your script to another system, then you may have problems.

I think some of the reason shell scripts tend to have lots of issues is that commonly one doesn’t learn shell scripting like “traditional” programming languages. Instead scripts tend to evolve from existing interactive command line use, or are based on existing scripts which themselves have propagated the limitations of ancient shell script interpreters.

It’s definitely worth spending the relatively small amount of time required to learn the shell script language correctly, if one uses linux/BSD/Mac OS X desktops or servers, where it is commonly used.