Essential UNIX Commands

File Operations

  • ls: Lists directory contents.
  • cp: Copies files and directories.
  • mv: Moves or renames files and directories.
  • rm: Removes files or directories.
  • mkdir: Creates directories.
  • rmdir: Removes empty directories.
  • touch: Creates an empty file or updates the file's timestamps.
  • ln: Creates links between files.
  • chmod: Changes the file mode (permissions).
  • chown: Changes file owner and group.
  • find: Searches for files in a directory hierarchy.

Text Processing

  • cat: Concatenates and displays files.
  • grep: Searches text using patterns.
  • sed: Stream editor for filtering and transforming text.
  • awk: Programming language for text processing.
  • sort: Sorts lines of text.
  • uniq: Reports or omits repeated lines.
  • cut: Removes sections from each line of files.
  • paste: Merges lines of files.
  • tr: Translates or deletes characters.
  • wc: Prints newline, word, and byte counts for each file.

System Operations

  • ps: Reports a snapshot of current processes.
  • top: Displays tasks and system status dynamically.
  • kill: Sends signals to processes.
  • nice: Modifies process scheduling priority.
  • nohup: Runs a command immune to hangups.
  • df: Reports file system disk space usage.
  • du: Estimates file space usage.
  • free: Displays amount of free and used memory in the system (common but not POSIX).
  • uptime: Shows how long the system has been running.


  • ping: Sends ICMP ECHO_REQUEST to network hosts.
  • ftp: Internet file transfer program.
  • ssh: Secure Shell for logging into and executing commands over a network.
  • scp: Secure copy (remote file copy program).
  • wget: Non-interactive network downloader.

Shell and Scripting

  • echo: Displays a line of text.
  • printf: Formats and prints data.
  • export: Sets or exports environment variables.
  • unset: Unsets a shell variable.
  • alias: Defines or displays aliases.
  • unalias: Removes aliases.

Archiving and Compression

  • tar: Archiving utility.
  • gzip: Compresses files.
  • gunzip: Decompresses files compressed by gzip.
  • zip: Package and compress (archive) files.
  • unzip: List, test, and extract compressed files in a ZIP archive.

System Information

  • uname: Prints system information.
  • man: Displays the manual page for other commands.
  • info: Reads documentation in Info format.
  • which: Locates a command.

POSIX (Portable Operating System Interface)

  • Description: A family of standards specified by the IEEE for maintaining compatibility between operating systems.
  • Scope: Includes definitions for system calls, command-line utilities, and shell scripting to ensure software compatibility.
  • Utilities: Defines a set of standard utilities like awk, sed, grep, cp, and many others.

LSB (Linux Standard Base)

  • Description: A standardization effort by the Linux Foundation to increase compatibility among Linux distributions.
  • Scope: Focuses on APIs, system commands, and libraries to ensure applications can run on any compliant Linux distribution.
  • Utilities: Specifies core utilities and libraries, ensuring a base level of system functionality and compatibility.

GNU Core Utilities (coreutils)

  • Description: A package of GNU software that provides basic file, shell, and text manipulation utilities common to GNU/Linux systems.
  • Scope: Replaces many of the traditional UNIX utilities with GNU versions, providing enhanced functionality and options.
  • Utilities: Includes essential utilities like ls, rm, mv, cat, chmod, and more.

BSD Core Utilities

  • Description: The set of tools and commands that come with BSD-based operating systems.
  • Scope: While not a standard per se, each BSD variant (FreeBSD, OpenBSD, NetBSD) provides a core set of utilities tailored to its environment.
  • Utilities: Includes commands like ps, ls, cp, which may have options or behavior specific to BSD systems.

Single UNIX Specification (SUS)

  • Description: An effort led by the Open Group to define a standard UNIX operating system environment.
  • Scope: Encompasses APIs, commands, and utilities for software compatibility across UNIX systems.
  • Utilities: Defines a wide range of commands and utilities similar to POSIX, as SUS incorporates the POSIX standard.