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
Name=value Create a variable called name and assign value to this variable.
$name Insert the value of name
$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
/ 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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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.
Click Here to download the above commands with detail
