Linux Shell - Basics

Introduction

In this document, the basics of a Linux shell will be explained. There will also be some usefull basic command’s listed, so you can start using the Linux shell immediately.

Background

What is a Shell?

A shell is the program that lets you interact with the operating system by typing commands. Bash (Bourne Again Shell) is the most common on Linux. The shell translates what you type into system calls that Linux understands.

The shell can run in different “modes”. For example, logging in through SSH starts a login shell, while opening a new terminal window in GNOME or KDE usually gives you a non-login shell. Understanding these differences matters because different startup files are read depending on the type of shell.

Note: Read Linux Shell - Scripting for more information about startup files.

What is TTY?

You’ll often see “tty” in Linux (for example /dev/tty1). TTY stands for teletypewriter. Back in the early days of UNIX, people interacted with big computers through physical terminals that worked like electric typewriters. Modern Linux still uses the word “tty” to mean “a terminal session.” Each virtual console (like pressing Ctrl+Alt+F3) is a different TTY.

So when we say login shell on a TTY, think: “a full user login, usually on a physical or SSH terminal.”

Startup Files

Different files are loaded when you log in. They are simply shell scripts that set environment variables, define aliases, or configure prompts.

• /etc/profile
  System-wide config for all users. Runs once at login. Sets PATH, umask, and other global defaults.

• ~/.profile
  User-specific login file for POSIX shells. Works for sh, dash, and sometimes Bash.

• ~/.bash_profile
  Bash-specific login file. Commonly used to load environment variables. Most people configure it to also source .bashrc.

• ~/.bashrc
  Runs for every interactive non-login shell. This is where you normally put aliases, functions, and prompt tweaks.

How They Work Together

Typical setup:

~/.bash_profile

export PATH=$PATH:$HOME/bin
[[ -f ~/.bashrc ]] && . ~/.bashrc

This way, when you log in, .bash_profile ensures .bashrc is also loaded.

💡 Rule of thumb:

• Use .bash_profile for environment variables that you want to be available everywhere (e.g., PATH changes).
• Use .bashrc for things like aliases, functions, and interactive tweaks.

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Usefull command’s

Command	Description
cp <source> <target>	Copy a file or directory
cp -r <source> <target>	Copy recursively, including subdirectories
mv <source> <target>	Move or rename a file/directory
rm <target>	Remove (delete) a file
rm -r <target>	Remove recursively, including subdirectories (DANGER!)
touch <target>	Create an empty file
mkdir <dir>	Create a new directory
rmdir <dir>	Remove an empty directory
grep <pattern> <file(s)>	Search for a pattern in file(s) Example: grep error /var/log/messages (Search for “error” in /var/log/messages)
find <path> -name <name>	Find files by name starting from a path Example: find / -name "*.log" (Find all .log files starting from root)