Command Line Interface

The Bash shell provides a history feature that records commands entered during previous sessions. This allows you to quickly recall, reuse, and manipulate commands from the past without having to type them again. The history feature is incredibly useful for streamlining your work in the terminal and for quickly repeating or modifying past commands. 1. What is Bash History? The Bash history refers to the list of commands that have been executed in the terminal. These commands are stored in a history file, which by default is located in the user's home directory as .bash_history. Location of history file: ~/.bash_history This file stores the commands you enter, allowing you to recall or search them later.

Environment variables in Bash are variables that define the environment in which processes run. They store system-wide values like system paths, configuration settings, and user-specific data, and can be accessed or modified within a Bash session. Environment variables are essential for: Configuring system settings. Customizing the behavior of scripts and programs. Storing configuration values for users and applications. Here’s an overview of how to work with environment variables in Bash. 1. Viewing Environment Variables To see all the current environment variables, use the env or printenv command: env or printenv This will print a list of all environment variables and their values.

The Bash prompt is the text that appears in your terminal before you type a command. By default, it displays minimal information, such as your username and current directory. Customizing your Bash prompt can enhance productivity by providing quick access to important information and making your terminal visually appealing. What is the Bash Prompt? The Bash prompt is controlled by the PS1 variable, which defines its appearance. For example: PS1="\u@\h:\w\$ " \u: Username. \h: Hostname. \w: Current working directory. \$: Displays $ for normal users and # for the root user. Enhanced Information: Display details like the current Git branch, exit status of the last command, or time.

Package managers are essential tools in modern operating systems (OS) that help automate the process of installing, updating, and removing software packages. These tools manage the software installed on a system, making it easier for users and administrators to keep their systems up-to-date with the latest versions of software. They provide a streamlined and efficient way to manage dependencies, handle software updates, and ensure system stability by preventing compatibility issues.

Signals are used to interact between processes and can occur at anytime, typically they are kill signals however processes can opt to handle them programatically unless they are SIGKILL or SIGSTOP signals.

A computer doing more than one thing at a time is using processes, these require resources, CPU time, memory and access to other devices like CD/DVD/USB drives, etc. Each process is allocated an amount of system resources to perform its function which is controlled by the operating system whose job it is to facilitate these processes. Signals have an important part to play on the interaction of the processes, usually these send exit signals and other information to each other, or to itself. Programs, Processes, and Threads A program is a set of instructions to be carried out which may local data such as information for output to the terminal via read or external data which may come from a database.

After reading this document you should be able to identify why Linux defines its filesystem hierarchy in one big tree and explain the role of the filesystem hierarchy standard, explain what is available at boot in the root directory (/), explain each subdirectory purpose and typical contents. The aim here is to be able to create a working bash script which knows where to put its different data stores including lockfiles, database(s) or temporary files; including the script itself. One Big Filesystem As with all Linux installations there is a set protocol to follow which could be looked at as one big tree starting from its root, /.

When it happens that your VPS is eating data by the second and there is disk read/write issues one port of call you are bound to visit is searching and identifying large files on your system. Now, you would have been forgiven for thinking this is a complicated procedure considering some Linux Bash solutions for fairly simple things, but no. Linux Bash wins again! du -sh /path/to/folder/* | sort -rh Here, du is getting the sizes and sort is organising them, -h is telling du to display human-readable format. The output should be something like this: 2.3T /path/to/directory 1.8T /path/to/other It does take a while to organise as it is being done recursively however given 3-5mins and most scenarios will be fine.

So yeah, getting used to Bash is about finding the right way to do things. However, learning one-liners and picking up information here and there is all very useful, finding something you don't need to Google in order to recall is extremely important. Take the case of recursive find and replace. We've all been there, it needs to be done frequently but you're either a) scared or b) forgetful. Then you use the same snippet from a web resource again and again and eventually make a serious error and boom, simplicity is now lost on you! So here it is, something you can remember so that you don't use different methods depending on what Google throws up today. grep -Rl newertext .