Classic Shell Scripting

Chapter 8. Production Scripts

In this chapter, we move on to some more-complex processing tasks. The examples that we consider are each of general utility, yet they are completely different from one another, and are absent from most Unix toolboxes.

The programs in this chapter include examples of command-line argument parsing, computing on remote hosts, environment variables, job logging, parallel processing, runtime statement evaluation with eval, scratch files, shell functions, user-defined initialization files, and consideration of security issues. The programs exercise most of the important statements in the shell language, and give a flavor of how typical Unix shell scripts are written. We developed them for this book, and they have proved to be solid production tools that we use, and rely on, in our daily work.

Path Searching

Some programs support searching for input files on directory paths, much like the Unix shell searches the colon-separated directory list in PATH for executable programs. This makes it easier for users, who can refer to files by shorter names and need not be aware of exactly where in the filesystem they are found. Unix doesn't provide any special commands or system calls for finding a file in a search path, even though there is historical precedent in other operating systems for such support. Fortunately, it isn't hard to implement a path search, given the right tools.

Rather than implement a path search for one particular program, let's write a new tool ...