Shell Arithmetic

• Use to perform arithmetic operations. Syntax:

  expr op1 math-operator op2
  

  Examples:

  $ expr 1 + 3
  $ expr 2 - 1
  $ expr 10 / 2
  $ expr 20 % 3
  $ expr 10 \* 3
  $ echo `expr 6 + 3`
  

  • Multiplication use $\backslash *$ and not $*$ since its wild card.
  • Before expr keyword we used ` (back quote) sign not the (single quote i.e. ') sign. expr is also end with ` i.e. back quote.
  • If you use double quote or single quote, it will NOT work.
• There are three types of quotes
  1. Double quotes (") - Anything enclose in double quotes removed meaning of that characters (except $\setminus$ and $).
  2. Single quotes (') - Enclosed in single quotes remains unchanged.
  3. Back quote (`) - To execute command

  $ echo "Today is date"
  $ echo "Today is `date`".