Master Essential Linux Shell Commands: A Complete Guide

Linux shell is a command interpreter that provides an interface between the user and the operating system, operating in a text‑based environment unlike graphical X Window.

Common Shells

Bourne shell (sh) : the default Unix shell, powerful for scripting but lacks interactive features.

C shell (csh) : adds interactive features like command completion and history; tcsh is its enhanced version.

Korn shell (ksh) : combines features of Bourne and C shells; pdksh is an enhanced variant.

Bash (bash) : the default shell on most Linux systems, compatible with Bourne shell and adds many improvements such as command completion, wildcard support, history, and aliases.

Typical Bash Features

Command line completion using Tab.

Wildcard patterns * and ? for flexible matching.

Command history stored in .bash_history, configurable via HISTSIZE.

Aliases defined with alias and removed with unalias.

Common Commands

Account and password : passwd Online help : man <command> Remote login : rlogin, telnet File and directory handling :

List files: ls with options -a, -t, -F, -l, -R Change directory: cd <path> Copy files/directories: cp (use -r for directories)

Move/rename: mv Create/remove directories: mkdir, rmdir, rm -r Delete files: rm with patterns ?, * File permissions : chmod (numeric or symbolic modes)

Ownership : chown, chgrp File timestamps : touch Links : ln, ln -s Search : grep, whereis, which, whatis, find Comparison : diff (use -r for directories)

Compression : compress, uncompress Pipelines : command1 | command2 Input/Output redirection : < file, > file, >> file, >& file Process control :

List processes: ps (options -aux, -x)

Terminate: kill (use -9 for force)

Background execution: command & Job control: jobs, kill %n Shell variables : view with set, access with echo $VAR, set with set VAR=value, unset with unset VAR Aliases : define with alias name='command', list with alias, remove with unalias History : configure length with set history=n, view with history, repeat with !!, !n, !string, or edit with ^old^new Network utilities : ping, talk Email : mail for sending messages, /usr/magedu/sendmail -bp to check queue

User and System Information

Current users: who, finger, w Switch user: su <user> Show current username: who am i, whoami List all logged‑in users on the network:

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