[bash] 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?

This question is related to bash unix command-line

The answer is

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

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

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.

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.

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"

pythonp "1 / (1+math.exp(0.5))"

# 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))"     

I have a simple script I use for this:

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


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).

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

echo "3 * 2.19" | bc -l 

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"


$ c '5*5'
$ c 5/5
$ c 3.4/7.9

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


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

Internal Methods

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

$ echo $(( 5 * 5 ))

External Methods

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

$ echo '5 * 5' | /usr/bin/bc

$ /usr/bin/expr 5 \* 5

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

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

Examples related to bash

Comparing a variable with a string python not working when redirecting from bash script Zipping a file in bash fails How do I prevent Conda from activating the base environment by default? Get first line of a shell command's output Fixing a systemd service 203/EXEC failure (no such file or directory) /bin/sh: apt-get: not found VSCode Change Default Terminal Run bash command on jenkins pipeline How to check if the docker engine and a docker container are running? How to switch Python versions in Terminal?

Examples related to unix

Docker CE on RHEL - Requires: container-selinux >= 2.9 What does `set -x` do? How to find files modified in last x minutes (find -mmin does not work as expected) sudo: npm: command not found How to sort a file in-place How to read a .properties file which contains keys that have a period character using Shell script gpg decryption fails with no secret key error Loop through a comma-separated shell variable Best way to find os name and version in Unix/Linux platform Resource u'tokenizers/punkt/english.pickle' not found

Examples related to command-line

Git is not working after macOS Update (xcrun: error: invalid active developer path (/Library/Developer/CommandLineTools) Flutter command not found Angular - ng: command not found how to run python files in windows command prompt? How to run .NET Core console app from the command line Copy Paste in Bash on Ubuntu on Windows How to find which version of TensorFlow is installed in my system? How to install JQ on Mac by command-line? Python not working in the command line of git bash Run function in script from command line (Node JS)