It’s only words, and words are all I have…

Using printf in BASH

In Linux we write a lot of shell scripts to help us automate things or ease complex tasks. Sometimes we need to display some information on the screen, so it’s pretty common to find quite a few echo statements lying about, like so:

echo $USERNAME
echo "I'm sorry Dave, I can't do that."

The command is also useful when we want to examine the contents of a variable from the command line. For example, to see the exit code of the most recently run command:

$ echo $?

The Baker Street Regulars

The Basics of Regular Expressions

Introduction

Unix administrators have long used regular expressions to help them locate files, modify data, and manage system configurations. Tools like grep and sed are designed to process regular expressions to provide the administrator with exactly the information he wants. While versions of these tools have been ported to Windows, most Windows administrators are unaware that they exist. Because of the limitations of the Windows command shell, Windows administrators typically stick with slower, more complicated graphical tools to manage the operating system.

Enter PowerShell. PowerShell is designed to be a replacement for the standard Windows shell, and it is far more powerful and flexible than its predecessor. Among the many command enhancements PowerShell offers is built-in support for regular expressions. It borrows this capability heavily from Perl, a scripting language that was developed specifically for processing text.

Regular expressions are used to search for character sequences inside text strings or files. Programs that process regular expressions look for text that matches a given pattern. The components of a regular expression are not complicated, but the available combinations are many and varied, making it possible to perform some very sophisticated matches. Whether you’re administering Windows, Linux, or the Unix-based macOS, you should invest some time learning the cryptic syntax of regular expressions so that you can manage systems and automate common tasks.

This tutorial will introduce regular expressions. It is not aimed at a particular operating system. Students of both Linux and PowerShell will come away with a basic knowledge of how regular expressions work and how to craft their own. Specific tools such as Linux’s grep command and PowerShell’s -match operator are covered in those respective classes at Centriq Training.