Linux BASH command line

alias    Create an alias
awk      Find and Replace text within file(s)

break    Exit from a loop
builtin  Run a shell builtin

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
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

date     Display or change the date & time
dc       Desk Calculator
dd       Data Dump - Convert and copy a file
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
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
du       Estimate file space usage

echo     Display message on screen
ed       A line-oriented text editor (edlin)
egrep    Search file(s) for lines that match an extended expression
eject    Eject CD-ROM
enable   Enable and disable builtin shell commands
env      Display, set, or remove environment variables
eval     Evaluate several commands/arguments
exec     Execute a command
exit     Exit the shell
expand   Convert tabs to spaces
export   Set an environment variable
expr     Evaluate expressions

factor   Print prime factors
false    Do nothing, unsuccessfully
fdformat Low-level format a floppy disk
fdisk    Partition table manipulator for Linux
fgrep    Search file(s) for lines that match a fixed string
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     Filesystem consistency check and repair.
function Define Function Macros

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)

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

id       Print user and group id's
if       Conditionally perform a command
import   Capture an X server screen and save the image to file
info     Help info
install  Copy files and set attributes

join     Join lines on a common field

kill     Stop a process from running

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
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)

m4       Macro processor
man      Help manual
mkdir    Create new folder(s)
mkfifo   Make FIFOs (named pipes)
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

nice     Set the priority of a command or job
nl       Number lines and write files
nohup    Run a command immune to hangups

passwd   Modify a user password
paste    Merge lines of files
pathchk  Check file name portability
popd     Restore the previous value of the current directory
pr       Convert text 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

quota    Display disk usage and limits
quotacheck Scan a file system for disk usage
quotactl Set disk quotas

ram      ram disk device
rcp      Copy files between two machines.
read     read a line from standard input
readonly Mark variables/functions as readonly
remsync  Synchronize remote files via email
return   Exit a shell function
rm       Remove files
rmdir    Remove folder(s)
rpm      Remote Package Manager
rsync    Remote file copy (Synchronize file trees)

screen   Terminal window manager
sdiff    Merge two files interactively
sed      Stream Editor
select   Accept keyboard input
seq      Print numeric sequences
set      Manipulate shell variables and functions
shift    Shift positional parameters
shopt    Shell Options
shutdown Shutdown or restart linux
sleep    Delay for a specified time
sort     Sort text files
source   Run commands from a file `.'
split    Split a file into fixed-size pieces
su       Substitute user identity
sum      Print a checksum for a file
symlink  Make a new name for a file
sync     Synchronize data on disk with memory

tac      Concatenate and write files in reverse
tail     Output the last part of files
tar      Tape ARchiver
tee      Redirect output to multiple files
test     Evaluate a conditional expression
time     Measure Program Resource Use
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

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

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')

xargs    Execute utility, passing constructed argument list(s)
yes      Print a string until interrupted

.period  Run commands from a file
###      Comment / Remark