book

Linux Command Line and Shell Scripting Techniques

by Vedran Dakic, Jasmin Redzepagic

March 2022

Beginner to intermediate

552 pages

11h 26m

English

Packt Publishing

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Technical requirements Accessing the shellGetting readyHow to do it…How it works…See alsoSetting up the user shellGetting readyHow to do it…How it works…Setting up the Bash shell Getting readyHow to do it…How it works…There's more…Using the most common shell commandsGetting readyHow to do it…How it works...Using screen Getting readyHow to do it…How it works…There's more…
Technical requirements Learning the basics of the Vi(m) Editor Getting readyHow to do it…How it works…See alsoLearning the basics of the nano editorGetting readyHow to do it…There's more…Going through the advanced Vi(m) settingsGetting readyHow to do it…How it works…There's more…
Technical requirements Process management toolsGetting readyHow to do it…How it works…See alsoManaging background jobsGetting readyHow to do it…How it works…There's more…Managing process prioritiesGetting readyHow to do it…How it works…There's more…Configuring crondGetting readyHow to do it…How it works…There's more…
Technical requirements Using nmcli and netplanGetting readyHow to do itHow it worksThere's moreUsing firewall-cmd and ufwGetting readyHow to do itHow it worksThere's moreWorking with open ports and connectionsGetting readyHow to do itHow it worksThere's moreConfiguring /etc/hosts and DNS resolvingGetting readyHow to do itHow it worksThere's moreUsing network diagnostic toolsGetting readyHow to do itHow it worksThere's more
Technical requirements Basic file and directory-based commandsGetting readyHow to do it…How it works…See alsoAdditional commands for manipulating file/directory security aspectsGetting readyHow to do it…How it works…See alsoManipulating text files by using commandsGetting readyHow to do it…How it works…There's more…Finding files and foldersGetting readyHow to do it…How it works…There's more…Archiving and compressing files and foldersGetting readyHow to do it…How it works…There's more…Managing services and targetsGetting readyHow to do it…How it works…There's more…
Technical requirements Using dnf and apt for package managementGetting readyHow to do it…How it works…There's more…Using additional repositories, streams, and profilesGetting readyHow to do it…How it works…Creating custom repositoriesGetting readyHow to do it…How it works…There's more…Compiling third-party softwareGetting readyHow to do it…How it works…There's more…
Technical requirements Learning how to use SSH and SCPGetting readyHow to do it…How it works…There's more…Learning how to use rsyncGetting readyHow to do it…How it works…There's more…Using vsftpdGetting readyHow to do it…How it works…There's more
Technical requirements Using text commands to merge file contentGetting readyHow to do it…How it works…There's more…Converting DOS text to Linux text and vice versaGetting readyHow to do it…How it works…There's more…Using cutGetting readyHow to do it…How it works…There's more…Using egrepGetting readyHow to do it…How it works…There's more…Using sedGetting readyHow to do it…How it works…There's more…

Technical requirements Writing your first Bash shell scriptGetting readyHow to do it…How it works…Serializing basic commands – from simple to complexGetting readyHow to do it…How it works…There's more…Manipulating shell script input, output, and errors Getting readyHow to do it…How it works…Shell script hygieneGetting readyHow to do it…There's more…
The for loopGetting readyHow to do it…How it works…See alsobreak and continueGetting readyHow to do it…How it works…See alsoThe while loopGetting readyHow to do it…How it works…See alsoThe test-if loopGetting readyHow to do it…How it works…See alsoThe case loopGetting readyHow to do it…How it works…See alsoLogical looping with and, or, and not Getting readyHow to do it…How it works…See also
Technical requirements Using shell variables Getting readyHow to do it…How it works…See alsoUsing variables in shell scripting Getting readyHow to do it…How it works…See alsoQuoting in the shell Getting readyHow to do it…How it works…See alsoPerforming operations on variables Getting readyHow to do it…How it works…See alsoVariables via external commands Getting readyHow to do it…How it works…See also
Technical requirements Using custom functions in shell script codeGetting readyHow to do it…How it works… See alsoPassing arguments to a function Getting readyHow to do it…How it works…See alsoLocal and global variablesGetting readyHow to do it…How it works…See alsoWorking with returns from a functionGetting readyHow to do it…How it works…See alsoLoading an external function to a shell scriptGetting readyHow to do it…How it works…See alsoImplementing commonly used procedures via functionsGetting readyHow to do it…How it works…See also
Technical requirements Basic array manipulationGetting readyHow to do it…How it works…See alsoAdvanced array manipulationGetting readyHow to do it…How it works…See also
Technical requirements Creating text-based interactive scriptsGetting readyHow to do it…How it works…See alsoUsing expect to automate repetitive tasks based on text outputGetting readyHow to do it…How it works…See alsoUsing dialog for menu-driven interactive scriptsGetting readyHow to do it…How it works…See also
Technical requirements Common scripting mistakesGetting readyHow to do it…How it works…See also…Simple debugging approach – echoing values during script executionGetting readyHow to do it…How it works…See alsoUsing the bash -x and -v optionsGetting readyHow to do it…How it works…See also…Using set to debug a part of the scriptGetting readyHow to do it…How it works…See also…
Technical requirements Creating a file and folder inventoryHow to do it…See alsoChecking if you're running as rootGetting readyHow to do it…See alsoDisplaying server statsGetting readyHow to do it…There's more…Finding files by name, ownership, or content type and copying them to a specified directoryGetting readyHow to do it…There's more…Parsing date and time dataGetting readyHow to do it…Configuring the most common firewall settings interactivelyGetting readyHow to do it…There's more…Configuring network settings interactivelyGetting readyHow to do it…There's more…Backing up the current directory with shell script arguments and variablesGetting readyHow to do it…There's more…Creating a current backup based on the user input for the backup source and destinationGetting readyHow to do it…There's more…
Technical requirements Implementing a web server service and security settingsGetting readyHow to do it…See alsoCreating users and groups and forcing users to change them on the next loginGetting readyHow to do it…See alsoCreating users and groups from a standardized input file and a random password for each userGetting readyHow to do it…See alsoScripted VM installation on KVMGetting readyHow to do it…See alsoUsing a shell script to provision SSH keysGetting readyHow to do it…See alsoA shell script for VM administrationGetting readyHow to do it…See also
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Content preview from Linux Command Line and Shell Scripting Techniques

Chapter 10: Using Loops

In the previous chapter, we started dealing with scripting, and we did a lot of learning about how scripts work and how they are structured. However, we missed a huge topic in scripting – influencing the order in which commands are executed when a script is run. There are a couple of things that we need to cover here, since there are multiple ways we can influence what is going to be the next command executed in a script.

We are going to start with a concept we call iterators or, more commonly, loops. There are a lot of things in everyday tasks that need to be done repeatedly, usually changing just one small thing in every iteration. This is where looping comes in.

We will cover the following recipes in this chapter: ...