Basic and Common commands

Before you turn over to the next chapter where you are going to meet a plethora of commands, remember a few things that apply to all UNIX commands.

•      All UNIX commands must always be entered in small case letters

•      Between the command name and the options that may be available with the command there must always be a space or a tab, for example, ls –l. Here is the command whereas –l is the option and the two have been separated by space. The option is usually preceded by a minus (-) sign. The option available with a command are often known as switches

•       Two or more options available with command can usually be combined, for example, the command ls –l –a is same as ls –la

•        If you make a typing mistake, press backspace to erase characters Don’t try back using arrow keys and then attempt deleting using the del key

•      To cancel the entire command before you press Enter, press ctrl+c Or del key

Basic Commands:

~]$ date             #To see the date of the system.

~]$ date +%d-%Y-%H-%M  #To see particular date format you always use date options

~]$ cal                #To see the current month calendar.

~]$ cal 11 2014            #To display the calendar, Month November (11) and year 2014


cal
      May 2016
Su Mo Tu We Th Fr Sa
 1  2  3  4  5  6  7
 8  9 10 11 12 13 14
15 16 17 18 19 20 21
22 23 24 25 26 27 28
29 30 31

~]$ clear            #To clear the screen

~]$ ls –l            #List files, directories with their properties

~]$ ls                   #To list files and directories

~]$ ls –a            #To list all hidden files and directories

~]$ ls –d            #To list only directories

 ~]$ pwd             #Print working directory

~]$ who am I    #To see from which user you have logged in

~]$ who             #To see all who is logged in yet this point of time from which IP

~]$ w                  #More details about user related info

 ~]$ uptime        #To see the server up time, boot time, users and load

 ~]$ uname –a     #Verify Operating system version, kernel version and architecture

~]$ touch <File Name>         #Create an empty file / Multiple empty files yet a time

Options:

~]$ touch –am                                   #it will change a file time to current time

~]$ touch –r file1 –B 30 file2  #it will create two files with 30 seconds time difference

~]$ cat /dev/null > file                       #To empty the data file

~]$ cat > <File Name>                      #Create an single file with text

       In above example two files 'kumar' and 'ravi' where created because we have provided the space in between 'kumar' and 'ravi' file names.

~]$ rm –rf <File / Directory Name>    #Delete files and directories forcefully

~]$rmdir <directory>    #Delete directories only

 ~]$ mkdir <Directory Name> #Create an empty directory / directories

~]$ mkdir –p <directory/directory/directory> #to create parent directories

 ~]$ cd <Path of the directory>         #Change directory

 ~]$ cat <File Name>              #View content of file

 ~]$ time             #Calculate response time of the activity / command

 ~]$ hwclock                  #to see detailed date and time with time zone

~]$ cp <Source path> <Destination path>  #Copy the files from one path to another path

~]$cp –Rv <source> <destination> #copy directories from source to destination

Options:

-R, -r,              #copy directories recursively

-v                     #verbose to see progress of copy job

-p                     #preserve

-f                      #forcefully

-I                     #interactive: Ask before overwriting file

 Copying directory must use –R to copy directories

 ~]$ mv <source> <destination>       #Move files/directories

~]$ mv <old name> <new name>    #Rename the file and directory

 ~]$ last                          #Check who logged in and when logged in duration

~]$ arch             #to know architecture

 

 ~]$ reboot / init 6                     #Restart server

~]$poweroff / init 0                  #To shut down the server

~]$ dmesg                                 #Check boot process logs

 ~]$ nsloookup <Server Address>    #check dns resolution

~]$ dig  <server address>      #check dns resolution to debug

~]$ tree <directory>               #it will show the tree of parent directory

~]$ stat <file name>               #detailed information about file

 ~]$ wc                            #word count, character count and line count

Options:

-l          #Check line count

-c         #Character Count

-w        #Word Count

 Help relate commands:

~]$ whatis <Command Name>  #It will display single line description about command

 ~]$ whereis <Command Name> #It will provide you path of the command

~]$ man <command>                 #manual page of the command

~]$ info <command>              #information about the command

~]$ <command> --help           #it will gives a command options and there usage

~]$ apropos <keyword>         #to know about the command use