Linux Command Line and Shell Scripting Bible, 3rd Edition

Basic Script Building

IN THIS CHAPTER

Using multiple commands

Creating a script file

Displaying messages

Using variables

Redirecting input and output

Pipes

Performing math

Exiting the script

Now that we've covered the basics of the Linux system and the command line, it's time to start coding. This chapter discusses the basics of writing shell scripts. You need to know these basic concepts before you can start writing your own shell script masterpieces.

Using Multiple Commands

So far you've seen how to use the command line interface (CLI) prompt of the shell to enter commands and view the command results. The key to shell scripts is the ability to enter multiple commands and process the results from each command, even possibly passing the results of one command to another. The shell allows you to chain commands together into a single step.

If you want to run two commands together, you can enter them on the same prompt line, separated with a semicolon:

$ date ; who
Mon Feb 21 15:36:09 EST 2014
Christine tty2         2014-02-21 15:26
Samantha tty3         2014-02-21 15:26
Timothy  tty1         2014-02-21 15:26
user     tty7         2014-02-19 14:03 (:0)
user     pts/0        2014-02-21 15:21 (:0.0)

$

Congratulations, you just wrote a shell script! This simple script uses just two bash shell commands. The date command runs first, displaying the current date and time, followed by the output of the who command, showing who is currently ...