Shell Scripting: Expert Recipes for Linux, Bash, and More

Summary

Variables are an essential part of any programming language, and while the shell’s syntax is sometimes complicated, it provides powerful capabilities, which in other languages are treated as arithmetic or string specific features. The shell’s variable syntax allows you to get substrings, do basic regular expressions, and so on with variables, by operating directly on the variables themselves. This means that there is no need for many functions, such as substr(), strlen(), and the like.

Chapter 3 explored almost all of the predefined variables, including variables such as PATH and PS1; COLUMNS and ROWS; RANDOM, $0, $1, $2, and so on; $* and $@, and all the things that they can be used for. This chapter has gone further into what can be done with user-defined variables, and the powerful transformations that the shell itself can do to their values.

Variables are used in any non-trivial script, so a good understanding of the basics is essential. For the more complex syntax, it is useful to have a basic reference to hand.

The next chapter looks at functions and libraries, which regularly make great use of variables. By combining variables with functions, serious computation is possible.