Multiplication on command line terminal

I'm using a serial terminal to provide input into our lab experiment. I found that using

$ echo "5X5" 

just returns a string of "5X5". Is there a command to execute a multiplication operation?

8 Answers

Yes, you can use bash's built-in Arithmetic Expansion $(( )) to do some simple maths

$ echo "$((5 * 5))" 25 

Check the Shell Arithmetic section in the Bash Reference Manual for a complete list of operators.

For sake of completeness, as other pointed out, if you need arbitrary precision, bc or dc would be better.

For more advanced and precise math consider using bc(1).

echo "3 * 2.19" | bc -l 6.57 

Internal Methods

Bash supports arithmetic expansion with $(( expression )). For example:

$ echo $(( 5 * 5 )) 25 

External Methods

A number of utilities provide arithmetic, including bc and expr.

$ echo '5 * 5' | /usr/bin/bc 25 $ /usr/bin/expr 5 \* 5 25 

The classical solution is:

 expr 5 \* 5 

expr will only work with integer operands. Another nice option is:

 echo 5 5\*p | dc 

dc can be made to work with non-integer operands.

A simple shell function (no sed needed) should do the trick of interpreting '5X5'

$ function calc { bc -l <<< ${@//[xX]/*}; }; $ calc 5X5 25 $ calc 5x5 25 $ calc '5*5' 25 

I use this function which uses bc and thus supports floating point calculations:

c () { local a (( $# > 0 )) && a="$@" || read -r -p "calc: " a bc -l <<< "$a" } 

Example:

$ c '5*5' 25 $ c 5/5 1.00000000000000000000 $ c 3.4/7.9 .43037974683544303797 

Bash's arithmetic expansion doesn't support floats (but Korn shell and zsh do).

Example:

$ ksh -c 'echo "$((3.0 / 4))"' 0.75 

I have a simple script I use for this:

me@mycomputer:~$ cat /usr/local/bin/c

#!/bin/sh echo "$*" | sed 's/x/\*/g' | bc -l 

It changes x to * since * is a special character in the shell. Use it as follows:

• c 5x5
• c 5-4.2 + 1
• c '(5 + 5) * 30' (you still have to use quotes if the expression contains any parentheses).

If you like python and have an option to install a package, you can use this utility that I made.

# install pythonp python -m pip install pythonp pythonp "5*5" 25 pythonp "1 / (1+math.exp(0.5))" 0.3775406687981454 # define a custom function and pass it to another higher-order function pythonp "n=10;functools.reduce(lambda x,y:x*y, range(1,n+1))" 3628800