Unix Shell Variables

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In Unix, there are two types of shell variables:

  1. System variables: Created and maintained by Unix itself. This type of variables will be defined in CAPITAL LETTERS.

       Example:

PATH, HOME etc..

  1. User defined variables: Created and maintained by user. This type of variables will be defined in lower letters.

        Example:

a, sum etc..

Examples of Systems Variables

  • HOME=/home/selva
  • PATH=/usr/bin:/sbin:/bin:/usr/sbin
  • SHELL=/bin/bash
  • USERNAME=selva

You can print any of the above variables contains as follows:

 

  • $ echo $USERNAME
  • $ echo $HOME

Ex:


User Variables:

Ex:

$ num=10

       To print the value of num  echo $num

Ex:


  • To define variable called ‘vech’ having value Bus:

               $ vech=Bus

  • To print contains of variable ‘n’ type command as follows:
  • $ echo $num
  • $ echo vech             # prints ‘vech’ instead its value ‘Bus’
  • $ echo num                   # prints ‘num’ instead its value ‘10’
  • You must use $ followed by variable name.

Ex:

Variables containing more than one word:

  • Often a variable has a value that contains space characters in it. If you try to set a variable containing spaces in the normal way, you will get an error message as follows.
  •  You should always use double quotes for the variables which has more than one word.
  • $ NAME=Mike Ron
  • sh: Ron: not found.

Ex:

  • $ NAME=”Mike Ron”
  • $ echo $NAME
  • Mike Ron

Ex:

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