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The
following basic commands are necessary to start working with Linux BASH
shell. The Linux commands and the worked out examples are shown one by one.
tty
The Linux
"tty" command display the name of the connected terminal.
Example:
[root@RHEL01
~]# tty
/dev/pts/0
Note: The
above terminal displayed is a pseudo-terminal.
which
The Linux
"which" command prints where in the search path an executable
binary is located.
Example:
[root@RHEL01
~]# which mail
/bin/mail
whoami
The Linux
"whoami" command displays who is the current user
Example:
[root@RHEL01
~]# whoami
root
echo
The Linux "echo"
command is used to print to the terminal.
Example
1 (Prints the given string to the terminal):
[root@RHEL01
~]# echo "hell world"
hell world
Example 2
(Prints the variable $USER to the terminal):
[root@RHEL01~]#echo$USER
root
Example 3
(Prints the variable $PWD to the terminal):
[root@RHEL01~]#echo$PWD
/root
clear
The Linux
"clear" command clears the terminal.
reset
The Linux
"reset" command resets the screen buffer
history
The Linux
"history" command displays the command history. The Linux
"history" command will display the entire command history. To
display a number of previous commands which are remembered, run the history command
with a number. The BASH command history is stored in
".bash_hostory", which is a hidden file at the home directory of
the Linux user. Usually the home directory of normal Linux user is
"/home/<user_name>", and the home directory of the super user
is "/root". Note that the up and down arrow keys can be used to
navigate through your command history.
Example 1
(This command will display ten commands executed previously) :
[root@RHEL01
~]# history 10
387 fdisk /dev/sdb 388 shut 389 fdisk -l 390 shut 391 echo $USER 392 reset 393 echo $PATH 394 reset 395 echo $PWD 396 history 10
Example 2
(This command will run the 387th command stored in history)
[root@RHEL01
~]# !387
fdisk /dev/sdb
The
number of cylinders for this disk is set to 1044.
There is nothing wrong with that, but this is larger than 1024, and could in certain setups cause problems with: 1) software that runs at boot time (e.g., old versions of LILO) 2) booting and partitioning software from other OSs (e.g., DOS FDISK, OS/2 FDISK)
Command
(m for help):
Example 3
(This command will run the previous command in history)
[root@RHEL01
~]# !!
fdisk /dev/sdb
The
number of cylinders for this disk is set to 1044.
There is nothing wrong with that, but this is larger than 1024, and could in certain setups cause problems with: 1) software that runs at boot time (e.g., old versions of LILO) 2) booting and partitioning software from other OSs (e.g., DOS FDISK, OS/2 FDISK)
Command
(m for help):
Note: Another command to manage hitory is fc. Using fc, you open the chosen command from history using the vi editor. The edited command runs when you exit the editor.
find
The Linux
"find" command can be used to find files using search patterns.
Example:
[root@RHEL01
~]# find / -name messages
/var/log/messages
locate
The Linux
"locate" command can be used to find the files fast in a Linux
machine. The locate command make use of a index database,
/var/lib/mlocate/mlocate.db. This index can be made current by using
‘updatedb’ command.
Example:
[root@RHEL01
~]# updatedb
[root@RHEL01 ~]# locate messages /var/log/messages
pwd
The Linux pwd command show
the name of the present working directory
Example:
[root@localhost bin]# pwd
/usr/bin
date
The Linux date command print
or set the system date and time
Example:
[root@localhost bin]# date
Sat Dec 26 11:49:39 IST 2009
shutdown
The Linux
shutdown command can be used to shutdown the system (halt) or restart the
system.
Example
(The first command shuts the computer immediatly and second command restarts
the computer immediatly:
[root@localhost bin]#
shutdown -h now
[root@localhost bin]#
shutdown -r now
cat
The Linux cat command sends
file contents to standard output. This is a way to list the contents of short
files to the screen.
Example:
[root@localhost ~]# cat
.bash_history
cd
The Linux cd command can be
used to change the working directory.
Examples:
[root@localhost ~]#cd /home (Changes the working directory to /home)
[root@localhost ~]#cd .. (Changes the working directory to the parent directory)
[root@localhost ~]#cd~(Changes the working directory to the users home
directory)
mv
The Linux
mv command is used to move a file from one location to another location.
Please refer the following link to learn more about the Linux mv
command.
cp
The Linux
cp command is used to copy a file from one location to another location. Please
refer the following link to learn more about the Linux cp
command.
df
The Linux
df command provides a very quick check of your file system disk space. Type
df -h to get a more easily readable version of the output.
[root@localhost
~]# df -h
Filesystem Size Used Avail Use% Mounted on /dev/sda2 14G 2.3G 11G 18% / /dev/sda1 99M 9.9M 84M 11% /boot tmpfs 252M 0 252M 0% /dev/shm
finger
The Linux
finger command allows you to see who else is on the computer or get detailed
information about a user who has access to the system.
The
following Linux finger command displays the who else are logged in on the
computer currently.
[root@localhost
~]# finger
Login Name Tty Idle Login Time Office Office Phone tintin tty3 Dec 27 12:20
The
following Linux finger commad displays detailed information about the user
tintin.
[root@localhost
~]# finger tintin
Login: tintin Name: (null) Directory: /home/tintin Shell: /bin/bash Never logged in. No mail. No Plan.
uptime
The Linux
uptime command returns useful system utilization information like . current
time, uptime in days, hours and minutes, connected users, load averaged -
1,5,15 minute values.
[root@localhost~]#uptime
12:25:01 up 15 min, 1 user, load average: 0.17, 0.16, 0.16
free
The Linus
free command returns memory utilization like Physical Memory (RAM), . Virtual
Memory (SWAP), The free command with option, “free –m” displays the output in
user friendly format (in MBs)
[root@localhost~]#free
-m
total used free shared buffers cached Mem: 503 466 37 0 34 355 -/+ buffers/cache: 76 426 Swap: 1027 0 1027
more and less
The Linux
"more" and "less" commands are paginators, which display text
one-page at a time. Less allows backward scrolling also.
file
The Linux
file command can be used to determine file type.
[root@localhost
~]# file anaconda-ks.cfg
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