Bash Shell Commands

What is a shell?

It is a shell's job to translate commands that a user has typed into a computer and translate it into such a language that the computer can understand.  Once the computer has carried out the instructions passed to it from the shell it then passes the output back to the shell which, in turn, translates this data back to user readable format.  The end result being output from the shell being displayed on the monitor.  It is important to remember that the shell itself is not an operating system - it is merely the interface between the user and the underlying operating system on the computer hard drive.

The shell has a number of pre-programmed commands on which a user can draw upon to complete tasks:

alias   -   Create an alias
awk   -   Find and Replace text, database sort/validate/index

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
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
fakse   -   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
ate   -   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

v   -   Verbosely list directory contents (`ls -l -b')
vdir   -   Verbosely list directory contents (`ls -l -b')
vi   -   Text Editor

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

.   -   Run commands from a file