Multiplication on command line terminal
BashUnixCommand LineBash Problem Overview
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?
Bash Solutions
Solution 1 - Bash
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.
Solution 2 - Bash
For more advanced and precise math consider using bc(1).
echo "3 * 2.19" | bc -l
6.57
Solution 3 - Bash
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
Solution 4 - Bash
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.
Solution 5 - Bash
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
Solution 6 - Bash
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 "$((3.0 / 4))"'
0.75
Solution 7 - Bash
I have a simple script I use for this:
me@mycomputer:~$ 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 5x5c 5-4.2 + 1c '(5 + 5) * 30'(you still have to use quotes if the expression contains any parentheses).
Solution 8 - Bash
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