Index of the Bash command line for Linux

A
alias		Create an alias
apropos		Search Help manual pages (man -k)
apt-get		Search for and install software packages (Debian/Ubuntu)
aptitude	Search for and install software packages (Debian/Ubuntu)
aspell		Spell Checker
awk		Find and Replace text, database sort/validate/index

B
basename	Strip directory and suffix from filenames
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		Concatenate and print (display) the content of files
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
groupadd	Add a user security group
groupdel	Delete a group
groupmod	Modify a group
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)
help		Display help for a built-in command
history		Command History
hostname	Print or set system name

I
iconv		Convert the character set of a file
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
jobs		List active jobs
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
link		Create a link to a file 
ln		Create a symbolic link to a file
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
mtr		Network diagnostics (traceroute/ping)
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
notify-send	Send desktop notifications
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
readarray	Read from stdin into an array variable
readonly	Mark variables/functions as readonly
reboot		Reboot the system
rename		Rename files
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
suspend		Suspend execution of this shell
sync		Synchronize data on disk with memory

T
tail		Output the last part of file
tar		Tape ARchiver
tee		Redirect output to multiple files
test		Evaluate a conditional expression
time		Measure Program running time
timeout		Run a command with a time limit
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)
uptime   	Show uptime
useradd		Create new user account
userdel		Delete a 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
wait		Wait for a process to complete
watch		Execute/display a program periodically
wc		Print byte, word, and line counts
whereis		Search the user's $path, man pages and source files for a program
which		Search the user's $path for a program file
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)
xdg-open	Open a file or URL in the user's preferred application
yes		Print a string until interrupted
.		Run a command script in the current shell
!!		Run the last command again
###		Comment / Remark