Mike Flippo, 123RF

Shell scripts: Equal rights for Unix derivatives and Linux

Vive la DiffÈrence

Article from ADMIN 02/2010

By Dr. Udo Seidel

Many system administrators manage Unix derivatives other than Linux, so shell scripts have to work across platforms.

The first lines of a shell script can be enough to cause administrators headaches. Many Linux distributions supply scripts written in Bash (Bourne Again Shell [1]), and, because not all Unix derivatives actually include a Bash shell, porting the scripts additionally means replacing the interpreter.

The Bourne shell is the interpreter of choice for this task. In fact, it should generally be your first choice because only the Bourne shell (Sh) guarantees maximum compatibility. But, again, some attention to detail is recommended.

Shell Game

More recent Linux distributions don't include a separate binary for the Bourne shell. Instead, they provide a subset of Bash. Thus, the pseudo-Sh doesn't react like a genuine Bourne shell.

A script written in this shell isn't really Bourne shell-compatible. You will notice this on Unix systems like Solaris [2], where unexpected results can sometimes confound users (Figure 1).