Linux and other Unix systems have strong scripting support. The whole idea of Unix, from the very beginning, was to make a system easy to develop on. One of these features is to take the output of one program and make it the input of another program—hence building new tools with existing programs. We should always keep this in mind when creating programs for Linux. The Unix philosophy is to make small programs that do one thing only—and do it well. By having many small programs that do only one thing, we can freely choose how to combine them. And by combining small programs, we can write shell scripts—a common task in Unix and Linux.
This chapter will teach us how to make programs that are easy to script and easy to interact with other programs. That way, other people will find them much more useful. It's even likely they will find new ways of using our programs that we haven't even thought of, making the programs more popular and easier to use.
In this chapter, we will cover the following recipes:
- Return values and how to read them
- Exiting a program with a relevant return value
- Redirecting stdin, stdout, and stderr
- Connecting programs using pipes
- Writing to stdout and stderr
- Reading from stdin
- Writing a pipe-friendly program
- Redirecting the result to file
- Reading environment variables
Let's get started!