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
Date Command Output


~]$ cal                #To see the current month calendar.
~]$ cal 11 2014            #To display the calendar, Month November (11) and year 2014
Cal Command Output

~]$ 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
ls -l Command output
 ~]$ pwd             #Print working directory
pwd Command output

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

~]$ who             #To see all who is logged in yet this point of time from which IP
~]$ w                  #More details about user related info
who command output
 ~]$ uptime        #To see the server up time, boot time, users and load
uptime Command Output
 ~]$ uname –a     #Verify Operating system version, kernel version and architecture
uname -a Command Output
~]$ 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
touch Command Output
       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
~]$rmdir <directory>    #Delete directories only
rm -rf Command Output
 ~]$ mkdir <Directory Name> #Create an empty directory / directories
~]$ mkdir –p <directory/directory/directory> #to create parent directories
mkdir Command Output
 ~]$ cd <Path of the directory>         #Change directory
cd Command Output and Usage

 ~]$ cat <File Name>              #View content of file
cat Command to read the file content
 ~]$ time             #Calculate response time of the activity / command
time Command Output
 ~]$ hwclock                  #to see detailed date and time with time zone
hwclock Command Output


~]$ 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
cp -v Command Output
 Copying directory must use –R to copy directories
cp -Rv Command Output
 ~]$ mv <source> <destination>       #Move files/directories
~]$ mv <old name> <new name>    #Rename the file and directory
mv Command Output
 ~]$ last                          #Check who logged in and when logged in duration
last Command Output
~]$ arch             #to know architecture
arch Command Output
 ~]$ reboot / init 6                     #Restart server
~]$poweroff / init 0                  #To shut down the server
~]$ dmesg                                 #Check boot process logs
dmesg Command Output
 ~]$ 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
stat Command Output
 ~]$ wc                            #word count, character count and line count
Options:
-l          #Check line count
-c         #Character Count
-w        #Word Count
wc Command Output
 Help relate commands:
~]$ whatis <Command Name>  #It will display single line description about command
whatis Command Usage
 ~]$ whereis <Command Name> #It will provide you path of the command
whereis Command Output
~]$ 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
apropos Command Output

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