Chapter 3. GNU and Unix Commands (Topic 1.3)

This Topic covers the ever-important aspect of working interactively with Linux command-line utilities. While it's true that GUI tools are already available to manage just about everything on a Linux system, a firm understanding of basic use of command-line utilities is essential.

The family of commands that are part of Linux and Unix systems has a long history. Individuals or groups that needed specific tools contributed many of the commands in the early days of Unix development. Those that were popular became part of the system and were accepted as default tools under the Unix umbrella. Today, Linux systems carry new, often more powerful GNU versions of these historical commands.

This section covers LPI Topic 1.3, GNU and Unix Commands. Even the Topic name implies the confusion that may exist regarding the origin of the commands we're using on GNU/Linux systems. Remember that for software to be freely distributed as part of your Linux distribution, it cannot be proprietary and must come with some form of redistribution ability in its licensing terms.

This LPI Topic has seven Objectives:

Objective 1: Work Effectively on the Unix Command Line

This Objective covers the essentials of working at the command line in a shell, including environment variables, using the command history and editing facilities, invoking commands, command substitution, and recursively executing commands. Weight: 4.

Objective 2: Process Text Streams Using Text-Processing Filters

There exists a diverse "toolbox" of interesting and powerful utilities from the GNU textutils package, which can be used to manipulate text in various ways. This Objective covers those utilities and how to use them. Weight: 7.

Objective 3: Perform Basic File Management

If you're used to an entirely GUI computing environment, performing basic file management manually from the command line may be awkward at first. You'll find, however, that after mastering a few simple commands you will achieve much finer control over file management chores. This Objective covers simple and recursive file management, including the use of wildcards (regular expressions). Weight: 2.

Objective 4: Use Unix Streams, Pipes, and Redirects

Among the most powerful concepts in the Linux and Unix worlds is the idea of creating text streams. This powerful tool offers you the ability to succinctly string various commands (such as those described in Objective 2) together into customized editing chains, which modify text in a serial fashion. Objective 4 includes redirection and the use of the tee command. Weight: 3.

Objective 5: Create, Monitor, and Kill Processes

Every running program on a Linux system is a process. Some processes are short-lived, like utility programs such as ls. Other processes, usually called daemons, are intended to run for extended periods or even constantly; these include processes such as web or database server software. Managing these processes is an important activity for a system administrator. This Objective covers foreground and background processing, process monitoring, signaling, and how to "kill" a process. Also covered are some of the commands used to manipulate running processes. Weight: 5.

Objective 6: Modify Process Execution Priorities

When you launch a process, you may wish to instruct the system to lower or raise its scheduling priority relative to the default. This action has the effect of giving more or less CPU time to your process. This is accomplished with the nice command, which modifies the default scheduling priority prior to running your command. This Objective covers these modifications. Weight: 2.

Objective 7: Perform Searches of Text Files Making Use of Regular Expressions

Many tools on your Linux system are capable of using regular expressions. At the most basic level, regular expressions are simply wildcard-matching mechanisms, such as you've probably used at the command line many times. While detailed use is beyond the scope of this book and the LPI exams, regular expressions are a powerful solution to a range of problems. This Objective covers basic regular expression usage with command-line tools such as sed and grep. Weight: 3.

The tools and concepts discussed here represent important and fundamental aspects of working with Linux, and are essential for your success on Exam 101.