Category: Scripting

Now that you’ve seen how to use the different ways to create loops in shell scripts, let’s look at some practical examples of how to use them. Looping is a common way to iterate through data on the system, whether it’s files in folders or data...

Sometimes, you may not want to display any output from your script. This often occurs if you’re running a script as a background process. If any error messages occur from the script while it’s running in the background, the shell e-mails them to the owner of the...

Iterating through a series of commands is a common programming practice. Often, you need to repeat a set of commands until a specific condition has been met, such as processing all the files in a directory, all the users on a system, or all the lines...

The until command works in exactly the opposite way from the while command. The until command requires that you specify a test command that normally produces a nonzero exit status. As long as the exit status of the test command is non-zero, the bash shell executes...

The while command is somewhat of a cross between the if-then statement and the for loop. The while command allows you to define a command to test and then loop through a set of commands for as long as the defined test command returns a zero...

So far, all you’ve seen in the if statement line are normal shell commands. You might be wondering if the bash if-then statement has the ability to evaluate any condition other than a command’s exit status code. The answer is no, it can’t. However, there’s a...

So far, you’ve seen two methods for displaying the output from your scripts: Displaying output on the monitor screen Redirecting output to a file Both methods produced an all-or-nothing approach to data output. There are times, however, when it would be nice to display some data...

Two additions to the bash shell provide advanced features that you can use in if-then statements: Double parentheses for mathematical expressions Double square brackets for advanced string handling functions The following sections describe each of these features in more detail.

Sometimes, you need to send the output of one command to the input of another command. This is possible using redirection, but somewhat clunky:

Another tool you have in your bash shell tool belt is the shift command. The bash shell provides the shift command to help you manipulate command line parameters. The shift command literally shifts the command line parameters in their relative positions. When you use the shift...