Creating Global Functions with the Korn Shell

Rainer Raab

Scripting and UNIX systems administration go hand in hand. Writing scripts to automate repetitive tasks is necessary if you want to find the time to work on other things, such as tightening security on the systems you manage, migrating applications to promote server utilization, capacity planning, and system tuning. These types of tasks often fall at the bottom of the food chain if you are in a typical shop, constantly putting out the fires started by buggy applications, compounded by poor vendor support, and unreliable hardware. They also lose priority if you are supporting a development team with a time to market of 3-6 months for their application and the developers expect you to manage the test, staging, and production environments, along with application deployment and installation scripts. Fortunately, most UNIX variants provide an ideal tool for developing and deploying scripts -- the Korn shell.

The Korn shell is not just a command interpreter; it provides a powerful and versatile programming language for the rapid development of automation scripts and the capability to write globally accessible functions. In its basic form, a Korn shell script is a series of shell commands, strung together in an executable file. In its most advanced form, a Korn shell script may utilize built-in shell commands that provide support for arrays, integer arithmetic and arithmetic conditions, advanced UNIX I/O redirectors, and functions. It is the support for functions that allows the rapid development of scripts that provide solutions to the tasks of routine UNIX systems administration.

Defining Global Functions

Korn shell functions, known as procedures or subroutines in other programming languages, allow for the organization of related shell commands by name. By organizing shell commands into functions, long shell scripts are easier to read and follow, and thus maintain.