You have a problem and you want to solve it with regular expressions? Now you have two problems! This is just one of the many regular expression jokes on the Internet.

In this section, you will learn how regular expressions work, as we will be using them in the upcoming chapters. We have prepared a file for our playground and if you want to try the grep commands on your own, you can take it from the GitHub repository.

Let's start by opening our text file so we can see its contents, and then splitting the screen so we can see both the file and the command side by side.

First of all, the simplest and probably the most common regular expression is to find a single word.

For this we will use the grep "joe" file.txt command:

joe is the string we are searching for and file.txt is the file where we perform the search. You can see that grep printed the line that contained our string and the word is highlighted with another color. This will only match the exact...

In this section, we will be looking at ways to improve your productivity using your shell. The Linux command line is great because it has a variety of tools we can use. What makes it even greater is the fact that we can chain these tools together to form greater, more powerful tools that will make us even more productive. We will not go into basic shell commands; instead we will be looking at some cool pipe and subshell combinations that can make our lives easier.

Let's start with a basic pipe; in this example, we are counting the length of the current path using the following command:

pwd | wc -c

pwd, as you probably know, stands for print working directory. The | is the pipe symbol, and what it does is send the output of the command on the left to the command on the right. In our case, pwd is sending its output to wc -c, which counts the number of characters. The coolest thing about pipes is that you can create a chain...

Pipes and subshells are one way of expanding the capabilities of our shell. The ultimate way is by writing shell scripts. These scenarios must be taken into consideration when dealing with complex tasks that can't be automated with a one-line command.

The good news is that almost all the tasks can be automated with the use of shell scripts. We won't go over an introduction to shell scripts. Instead, we will be looking at some more advanced use cases for writing them.

Let's start our journey into shell scripting! First thing, let's open a file called script.sh and split the screen so that we can test while writing. Every shell should start with #!, followed by the interpreter it uses. This line is called a shebang. We will be using bash as our default interpreter.

It's a good idea to use bash, because it's a common interpreter that comes with most Linux distributions and also OS X:

#!/bin/bash

Let's start with a simple use...

To really take advantage of automating tasks using shell scripts, it's important to organize all common tasks into reusable commands and have them available in the path. To do this, it's a good idea to create a bin folder inside the home directory for the scripts, and a bin/lib directory for storing common pieces of code. When working with lots of shell scripts, it's important to reuse large pieces of functionality. This can be achieved by writing library functions for your shell scripts, functions that you can call from multiple places.

Here we will create a library script called util.sh, which will be sourced in other scripts. By sourcing the script, we get access to functions and variables from inside the library script.

We will start by adding the print_ip function from a previous script.

Now we will add another function called getarg, which will be used by other scripts for reading command line arguments and values. We will simply paste it from...