a

alias

Create an alias apropos  Search Help manual pages (man -k)

apt-get

Search for and install software packages (Debian)

aspell

Spell Checker

awk

Find and Replace text, database sort/validate/index

b

bash

GNU Bourne-Again SHell

bc

Arbitrary precision calculator language

bg

Send to background

break

Exit from a loop

builtin

Run a shell builtin

bzip2

Compress or decompress named file(s)

c

cal

Display a calendar

case

Conditionally perform a command

cat

Display the contents of a file

cd

Change Directory

cfdisk

Partition table manipulator for Linux

chgrp

Change group ownership

chmod

Change access permissions

chown

Change file owner and group

chroot

Run a command with a different root directory

chkconfig

System services (runlevel)

cksum

Print CRC checksum and byte counts

clear

Clear terminal screen

cmp

Compare two files

comm

Compare two sorted files line by line

command

Run a command – ignoring shell functions

continue

Resume the next iteration of a loop

cp

Copy one or more files to another location

cron

Daemon to execute scheduled commands

crontab

Schedule a command to run at a later time

csplit

Split a file into context-determined pieces

cut

Divide a file into several parts

d

date

Display or change the date & time

dc

Desk Calculator

dd

Convert and copy a file, write disk headers, boot records

ddrescue

Data recovery tool

declare

Declare variables and give them attributes

df

Display free disk space

diff

Display the differences between two files

diff3

Show differences among three files

dig

DNS lookup

dir

Briefly list directory contents

dircolors

Colour setup for `ls’

dirname

Convert a full pathname to just a path

dirs

Display list of remembered directories

dmesg

Print kernel & driver messages

du Estimate file space usage

e

echo

Display message on screen

egrep

Search file(s) for lines that match an extended expression

eject

Eject removable media

enable

Enable and disable builtin shell commands

env

Environment variables

ethtool  Ethernet card settings

eval

Evaluate several commands/arguments

exec

Execute a command

exit

Exit the shell

expect

Automate arbitrary applications accessed over a terminal

expand

Convert tabs to spaces

export

Set an environment variable

expr

Evaluate expressions

f

false

Do nothing, unsuccessfully

fdformat

Low-level format a floppy disk

fdisk

Partition table manipulator for Linux

fg

Send job to foreground

fgrep

Search file(s) for lines that match a fixed string

file

Determine file type

find

Search for files that meet a desired criteria

fmt

Reformat paragraph text

fold

Wrap text to fit a specified width.

for

Expand words, and execute commands

format

Format disks or tapes

free

Display memory usage

fsck

File system consistency check and repair

ftp

File Transfer Protocol

function

Define Function Macros

fuser

Identify/kill the process that is accessing a file

g

gawk

Find and Replace text within file(s)

getopts

Parse positional parameters

grep

Search file(s) for lines that match a given pattern

groups

Print group names a user is in

gzip

Compress or decompress named file(s)

h

hash

Remember the full pathname of a name argument

head

Output the first part of file(s)

history

Command History

hostname

Print or set system name

i

id

Print user and group id’s

if

Conditionally perform a command

ifconfig

Configure a network interface

ifdown

Stop a network interface

ifup

Start a network interface up

import

Capture an X server screen and save the image to file

install

Copy files and set attributes

j

join

Join lines on a common field

k

kill

Stop a process from running

killall  Kill processes by name

l

less

Display output one screen at a time

let

Perform arithmetic on shell variables

ln

Make links between files

local

Create variables

locate

Find files

logname

Print current login name

logout

Exit a login shell

look

Display lines beginning with a given string

lpc

Line printer control program

lpr

Off line print

lprint

Print a file

lprintd

Abort a print job

lprintq

List the print queue

lprm

Remove jobs from the print queue

ls

List information about file(s)

lsof

List open files

m

make

Recompile a group of programs

man

Help manual

mkdir

Create new folder(s)

mkfifo

Make FIFOs (named pipes)

mkisofs

Create an hybrid ISO9660/JOLIET/HFS filesystem

mknod

Make block or character special files

more

Display output one screen at a time

mount

Mount a file system

mtools

Manipulate MS-DOS files

mv

Move or rename files or directories

mmv

Mass Move and rename (files)

n

netstat

Networking information

nice

Set the priority of a command or job

nl

Number lines and write files

nohup

Run a command immune to hangups

nslookup

Query Internet name servers interactively

o

open

Open a file in its default application

op

Operator access

p

passwd

Modify a user password

paste

Merge lines of files

pathchk

Check file name portability

ping

Test a network connection

pkill

Stop processes from running

popd

Restore the previous value of the current directory

pr

Prepare files for printing

printcap

Printer

capability database

printenv

Print environment variables

printf

Format and print data

ps

Process status

pushd

Save and then change the current directory

pwd

Print Working Directory

q

quota

Display disk usage and limits

quotacheck

Scan a file system for disk usage

quotactl

Set disk quotas

r

ram

ram disk device

rcp

Copy files between two machines

read

read a line from standard input

readonly

Mark variables/functions as readonly

reboot

Reboot the system

renice

Alter priority of running processes

remsync

Synchronize remote files via email

return

Exit a shell function

rev

Reverse lines of a file

rm

Remove files

rmdir

Remove folder(s)

rsync

Remote file copy (Synchronize file trees)

s

screen

Multiplex terminal, run remote shells via ssh

scp

Secure copy (remote file copy)

sdiff

Merge two files interactively

sed

Stream Editor

select

Accept keyboard input

seq

Print numeric sequences

set

Manipulate shell variables and functions

sftp

Secure File Transfer Program

shift

Shift positional parameters

shopt

Shell Options

shutdown

Shutdown or restart linux

sleep

Delay for a specified time

slocate

Find files

sort

Sort text files

source

Run commands from a file `.’

split

Split a file into fixed-size pieces

ssh

Secure Shell client (remote login program)

strace

Trace system calls and signals

su

Substitute user identity

sudo

Execute a command as another user

sum

Print a checksum for a file

symlink

Make a new name for a file

sync

Synchronize data on disk with memory

t

tail

Output the last part of files

tar

Tape ARchiver

tee

Redirect output to multiple files

test

Evaluate a conditional expression

time

Measure Program running time

times

User and system times

touch

Change file timestamps

top

List processes running on the system

traceroute

Trace Route to Host

trap

Run a command when a signal is set(bourne)

tr

Translate, squeeze, and/or delete characters

true

Do nothing, successfully

tsort

Topological sort

tty

Print filename of terminal on stdin

type

Describe a command

u

ulimit

Limit user resources

umask

Users file creation mask

umount

Unmount a device

unalias

Remove an alias

uname

Print system information

unexpand

Convert spaces to tabs

uniq

Uniquify files

units

Convert units from one scale to another

unset

Remove variable or function names

unshar

Unpack shell archive scripts

until

Execute commands (until error)

useradd

Create new user account

usermod

Modify user account

users

List users currently logged in

uuencode

Encode a binary file

uudecode

Decode a file created by uuencode

v

v

Verbosely list directory contents (`ls -l -b’)

vdir     Verbosely list directory contents (`ls -l -b’)

vi

Text Editor

vmstat

Report virtual memory statistics

w

watch Execute/display a program periodically

wc

Print byte, word, and line counts

whereis

Report all known instances of a command

which

Locate a program file in the user’s path.

while

Execute commands

who

Print all usernames currently logged in

whoami

Print the current user id and name (`id -un’)

Wget

Retrieve web pages or files via HTTP, HTTPS or FTP

write

Send a message to another user

x

xargs

Execute utility, passing constructed argument list(s)

yes

Print a string until interrupted

. Run a command script in the current shell

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