W3Professors

login       Access computer; start interactive session

Syntax:  login [username]

logout    Exits the current session

Syntax:  logout

shutdown        Shuts down your Linux system in a way that prevents damage to the file system

Syntax: shutdown [options] time [message]

Options

-f         reboots quickly without checking the filesystem
-h         halt the system after shutdown
-r         restart the computer

su             Creates a new shell session with a different user id and privileges

Syntax:  su [username]

tty                        Displays the number of terminal devices that are currently in use

Syntax:  tty

cal            Displays a calendar of the current year

Syntax:  Cal [option][month][year]

Options

-j         displays the calendar using Julian dates, with the days numbered from 1 sequentially to the end of the year

-y        Display a calendar for the entire year

date                     Displays the current date and time as traced by the system clock

Syntax:  date [option][date]

Options

-u         displays the date and time in GMT format
-s          set the date

hostname        Displays the system’s network identification name (hostname)

Syntax:  hostname [option][hostname]

Options

-a        displays the hostname alias
-i         display the ip address
-d        displays the name of the domain to which the host belongs

man        Displays text only manual pages and is the quick way to get information of most of the utilities installed to the system.

Syntax: man[options][section][title]

Options

-a         list all the man pages that match the title
-d        displays debugging information
-k         lists short description of all the man pages that match the specified string

pwd   This command shows the full path of the current directory

Syntax:        pwd

uname         Provides the wealth of information about the system you are using i.e it returns the name of the OS

Syntax:        uname[option]

Option                    

-a        all available information
-m       type of processor in use
-n        Displays the computer’s host name

uptime         Displays the current time, The amount of time the system has been running in the current session

users              Displays the total number of users currently working in the current session

who               Displays the name of the users currently logged into the system.

Syntax:        Who[option]

Options

-h                     display column heading
--help             lists available options

whoami                   Displays the username of the user currently logged in to the terminal session

bash Starts the bash shell.

Syntax:        Bash[option][filename]

Options

-c          Read commands from the specified string
-i         Starts bash as an interactive shell

bg       places the process in the background

Syntax:        bg[jobid]

env    It  displays or sets the specified variables.

Syntax:        env[option][variable=value][command]

Options

-u        unset the specified variable
-i         ignore the current environment

jobs   Lists all running or suspended jobs

Syntax:        Jobs[option][jobid]

Options

-l         list job Ids and Process ids
-n        lists all altered jobs
-p        lists process ids only

kill     Terminates the specified process

Syntax:        kill[option][id]

Options

-l            list the available signal names and numbers
-s            Specifies the signal by name

killall           kills all the processes

Syntax:        killall[option][name]

Options

-e        Require an exact match of long names
-i         Asks for confirmation before killing

ps                Displays the list of running processes

Syntax:        Ps[option][sort key][output field]

Options
-a        shows all processes on the current terminal
-e        shows all processes
-h        Shows the process hierarchy

suspend      suspends a command

Syntax:        suspend

tee     accepts output from the specified command and “splits” the output to the standard output

Syntax:        command|tee[option]filename

Options

-a        Append to the file
-i         ignore interrupt signal

cd       Change the current directory

Syntax:        cd [directory|path name]

dir      Lists the files in the current directory in case-sensitive,alphabetical order,using a columnar format.

Syntax:        dir [option][pattern]

Options

-1        list entries using one line for each filename
-a        shows all files including hidden files
-c         lists files sorted by the time of the last modification to the file’s status

find   This command searches the current directory for files with names that match the specified shell pattern.

Syntax:        find pattern

ls        Lists the files in the current directory in case sensitive alphabetical order using a columnar format.

Syntax:        ls [option][pattern]

Options

-l            Lists files in long listing format

chgrp            Change the ownership of the specified file to the specified group.

Syntax:        chgrp [option] group file

Options

-c                     Display message only when changes are made
-f                     hide messages
--help            display available options
   

chmod         changes the permission settings of the filename to the mode.

Syntax:        chmod [option] mode filename

Options

-c               Display message only when changes are made
-f                hide messages
--help      display available options

chown                Change the ownership of the specified file to the specified user.

Syntax:  chown [option] user [.group] file

Options

-c                      Display message only when changes are made
-f                     hide messages
--help            display available options

cp             copies one source file to the destination file

Syntax:  cp [option][source][destination]

Options

-a         create archive copies of the files.
-b         makes a backup copy
-f          remove existing destination file

dd             Copies the file and performs various conversations at the same time.

Syntax:  dd [option]

Options

bs        specify the size of the input and output bit streams in bytes.
Cbs      specify the number of bytes to convert at a time

ln              Creates a hard link to the specified target file.

Syntax:  ln [option] target [link name]

Options

-b          make a backup copy
-d         creates hard links to directories
-f         remove existing destination files.

Mkdir     Creates a specified directory.

Syntax:  mkdir [option] directory

Options

-m       creates the directory with the specifie permissions.
-p        makes parent directory.

mv           renames or moves one source file to a destination file or moves multiple source file to a destination that must be an existing directory.

Syntax:  mv [option][source][destination]

Options

-b         backup copy
-f          remove existing destination file
-i         prompt before overwriting existing destination file.

Rm           removes the specified file

Syntax:  rm [option] [file]

Options

-d         unlink the directory even if it is non empty.
-f         ignore non existent files
-i          prompt before overwriting existing destination file.

Rmdir    removes the specified directory but only if it is empty.

Syntax:  rmdir[option] directory

Options

-p        removes associated parent directory

Touch     It changes the time of the last access or modification of the specified filename to the current time.

Syntax:  touch [option] filename

Options

-a              changes the access time but no other times
-c               do not create any file.

Undelete    restores files deleted earlier using safedelete command

Syntax:  undelete [option][filename]

Options

-i          Displays information about the file
-l         Display a list of safedeleted files that can be restored.

Wc     Display line, word  and character count for the specified filename.

Syntax:  wc [option][filename]

Options

-c          Show the character count only
-l         Show the line count only
-w       Show the word count only

Df                   Displays the amount of disk space used and remaining on all mounted filesystems.

Syntax:  df [option] [filename]

Options

-a        include all filesystems
-h        displays sizes in a human readable format

Du      Displays the amount of disk space used in the current directory.

Syntax:  du [option][filename]

Options

-a        Show sizes of individual file
-c         Print the grandtotal of all arguments after all have been processed.

Fdisk                        Launches a menu driven program that partitions a hard disk

Syntax:  fdisk [option] device

Options

-l         List the current partition table
-s         Display the size of the specified partition
-v         Display the version number.

Mount          Attaches the device to the specified directory, which will serve as the filesystem’s mount point.

Syntax:  mount [option] device [directory]

Options

-a              Mount all the filesystems listed in /etc/fstab, except those set to noauto
-r               Mount the device as read only
-h              Display the available options.

Cat     Displays the specified filename on the standard output.

Syntax:  cat [option] [filename]

Options

-e        Display control and non-printing characters
-n        Number all output lines

Cmp  Compares the two specified files to determine whether any difference exist.

Syntax:  cmp [option] filename1 filename2

Options

-l         Print the Byte numbers of each difference and show the differing values
-s         Indicate nothing but generate the exit codes.
-c          Print the differing bytes as characters.

Cut     Displays a range of characters from the specified filename.

Syntax:  cut [option][filename]

Options

-b        output only the bytes specified by range
-c         Output only the character specified by range

Grep  Searches filename for lines that match a regular expression.

Syntax:  grep [option] regexp [filename]

Options

-a        Display n lines of trailing context after matching lines
-b        Display the byte offset in the input file before each line of output.

Sort   Sorts the specified filename line by line in character order.

Syntax:  sort [option][filename]

Options

-b         Ignore leading blanks
-d         Use only alphanumeric characters in keys
-f         converts lowercase to uppercase characters in keys

Uniq  Removes duplicate lines from a sorted input file and writes to the output file.

Syntax:  Uniq [option][input file][output file]

Options

-c         Prefix lines by the number of occurrences
-d        print the duplicate lines
-i   ignore case

PARAMETER EXPANSION

A shell parameter is an entity that stores a value(which is null). Among the various types of shell parameters are variables. You can create your own variable. Besides this there are several Built in variables as well.

How to create a variable?

Name=value    Create a variable called name and assign value to this variable.
$name               Insert the value of name

BUILT IN VARIABLES

$BASH                      The location of bash
$BASH_ENV              The location of the current .bashrc file in use
$BASH_VERSION       The version number of bash
$CDPATH                  The path to be used when cd is used
$DIRSTACK                An array variable containing the current contents of the directory stack
$FCEDIT                    The text editor used by default for the fc command
$FIGNORE                 A colon-separated list of suffixes to ignore when performing filename     completion

Standard Directory Structure

Directory          Purpose
/                          The root directory
/bin                     Start-up programs and commands used in single-user mode
/boot                  Files used to start the system
/dev                    Special files representing system files
/etc                    System – level configuration files and scripts
/home                 The user’s home directory
/lib                      Shared library files
/mnt                   The mount point for temporary file systems
/opt                    The installation directory for commercial software
/root                   The home directory for home user.
/tmp                   The storage space for temporary file
/usr                     The storage space for files that need to be made available system wide
/var                     Data file of variable length.

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