Doing math on the Linux command line

You can also assign values to variables and use those variable names in your calculations as shown in the examples below.

$ num1=11
$ num2=17
$ expr $num1 + $num2
28

The expr command can also work to some extent with strings. The expressions below reports the length of the string provided, but not counting the quotes.

$ expr length "hello"
5
$ expr length "Don't spend a day without having a little fun!"
46

Comparing strings with expr

The expr command also provides a way to compare strings, but note how the longer string must be provided first.

$ expr Linux : Linux
5
$ expr LinuxNow : Linux
5
$ expr Linux : LinuxNow
0

Getting help

You can get some help on using the expr command by using the –help option (expr –help). The bulk of this will explain how the various expressions work. It includes explanations such as these:

Print the value of EXPRESSION to standard output.  A blank line below
separates increasing precedence groups.  EXPRESSION may be:

  ARG1 | ARG2       ARG1 if it is neither null nor 0, otherwise ARG2
  ARG1 & ARG2       ARG1 if neither argument is null or 0, otherwise 0
  ARG1 < ARG2       ARG1 is less than ARG2
  ARG1 <= ARG2      ARG1 is less than or equal to ARG2
  ARG1 = ARG2       ARG1 is equal to ARG2
  ARG1 != ARG2      ARG1 is unequal to ARG2
  ARG1 >= ARG2      ARG1 is greater than or equal to ARG2
  ARG1 > ARG2       ARG1 is greater than ARG2
  ARG1 + ARG2       arithmetic sum of ARG1 and ARG2
  ARG1 - ARG2       arithmetic difference of ARG1 and ARG2
  ARG1 * ARG2       arithmetic product of ARG1 and ARG2
  ARG1 / ARG2       arithmetic quotient of ARG1 divided by ARG2
  ARG1 % ARG2       arithmetic remainder of ARG1 divided by ARG2
  STRING : REGEXP   anchored pattern match of REGEXP in STRING

The commands below are examples of expr commands.

$ expr 60 / 30 * 100
200
$ expr 20 / 30 * 100
0

Oops! What happened in the second example above? The expr command is not going to hold onto numbers less than 0. So, you need to use some other command.