PROBLEM:

• Using echo “20+5” literally produces the text “20+5”.
• What command you use to get the numeric sum, 25 in this case?
• Also, what’s the easiest way to do it just using bash for floating point? For example, echo $((3224/3807.0)) prints 0 :(.
• You are looking for answers using either the basic command shell (‘command line’) itself or through using languages that are available from the command line.

SOLUTION 1:

You could use bc. E.g.,

$ echo "25 + 5" | bc
30

Alternatively bc <<< 25+5 will also work.

Or interactively, if you want to do more than just a single simple calculation:

$ bc
bc 1.06.95
Copyright 1991-1994, 1997, 1998, 2000, 2004, 2006 Free Software Foundation, Inc.
This is free software with ABSOLUTELY NO WARRANTY.
For details type `warranty'. 
25 + 5
30

bc -q will jump into bc right away without the header/copyright info. For more information see the bc man page

This page also shows how to set up an alias or function to do calculation like this:

•  get the result

c "25 + 5" 

SOLUTION 2:

You can use calc:

If you just enter calc with no other arguments it enters an interactive mode where you can just keep doing math.

You exit this by typing exit:

C-style arbitrary precision calculator (version 2.12.3.3)
Calc is open software. For license details type:  help copyright
[Type "exit" to exit, or "help" for help.]
; 2+4
6
; 3+5
8
; 3.4+5
8.4
; 2^4
16
; exit

Or you use it with the expression as an argument and it will provide the answer and then exit

$calc 2 + 4
    6
$

calc is similar to bc

SOLUTION 3:

There are many ways to calculate.

For simple expressions you can use bash itself:

echo $((20+5))

or expr:

expr 20 + 5

And for complex cases there is great tool bc:

    echo "20+5" | bc

bc can calculate even very complex expression with roots, logarithms, cos, sin and so on.

SOLUTION 4:

Integer Math:

Performing Math Calculation in Bash:

First way to do math with integer (and only integer) is to use the command “expr — evaluate expression”.

Mac-n-Cheese:~ nicolas$ expr 1 + 1
2
Mac-n-Cheese:~ nicolas$ myvar=$(expr 1 + 1)
Mac-n-Cheese:~ nicolas$ echo $myvar
2
Mac-n-Cheese:~ nicolas$ expr $myvar + 1
3
Mac-n-Cheese:~ nicolas$ expr $myvar / 3
1
Mac-n-Cheese:~ nicolas$ expr $myvar \* 3
9

When doing a “multiply by” make sure to backslash the “asterisk” as it’s a wildcard in Bash used for expansion.

Another alternative to expr, is to use the bash builtin command let.

Mac-n-Cheese:~ nicolas$ echo $myvar
6
Mac-n-Cheese:~ nicolas$ let myvar+=1
Mac-n-Cheese:~ nicolas$ echo $myvar
7
Mac-n-Cheese:~ nicolas$ let myvar+1
Mac-n-Cheese:~ nicolas$ echo $myvar
7
Mac-n-Cheese:~ nicolas$ let myvar2=myvar+1
Mac-n-Cheese:~ nicolas$ echo $myvar2
8

Also, you can simply use the parentheses or square brackets :

Mac-n-Cheese:~ nicolas$ echo $myvar
3
Mac-n-Cheese:~ nicolas$ echo $((myvar+2))
5
Mac-n-Cheese:~ nicolas$ echo $[myvar+2]
5
Mac-n-Cheese:~ nicolas$ myvar=$((myvar+3))

This allow you to use C-style programming :

Mac-n-Cheese:~ nicolas$ echo $myvar
3
Mac-n-Cheese:~ nicolas$ echo $((myvar++))
3
Mac-n-Cheese:~ nicolas$ echo $myvar
4
Mac-n-Cheese:~ nicolas$ echo $((++myvar))
5
Mac-n-Cheese:~ nicolas$ echo $myvar
5

SOLUTION 5:

Floating point arithmetic:

You can’t do floating point arithmetic natively in bash, you will have to use a command line tool, the most common one being “bc – An arbitrary precision calculator language”.

Mac-n-Cheese:~ nicolas$ bc
bc 1.06
Copyright 1991-1994, 1997, 1998, 2000 Free Software Foundation, Inc.
This is free software with ABSOLUTELY NO WARRANTY.
For details type `warranty'.
3*5.2+7/8
15.6
15.6+299.33*2.3/7.4
108.6

you can use the STDIN to send your formula to “bc” then get the output on STDOUT.

Mac-n-Cheese:~ nicolas$ echo "3.4+7/8-(5.94*3.14)" | bc
-15.25

using the here-doc notation:

Mac-n-Cheese:~ nicolas$ bc <<< "3.4+7/8-(5.94*3.14)"
-15.25

The “scale” variable is really important for the precision of your results, especially when using integers only (Note: you can also use “bc -l” to use mathlib and see the result at max scale) .

Mac-n-Cheese:~ nicolas$ echo "2/3" | bc
0
Mac-n-Cheese:~ nicolas$ echo "scale=2; 2/3" | bc
.66
Mac-n-Cheese:~ nicolas$ echo "(2/3)+(7/8)" | bc
0
Mac-n-Cheese:~ nicolas$ echo "scale=2;(2/3)+(7/8)" | bc
1.53
Mac-n-Cheese:~ nicolas$ echo "scale=4;(2/3)+(7/8)" | bc
1.5416
Mac-n-Cheese:~ nicolas$ echo "scale=6;(2/3)+(7/8)" | bc
1.541666
Mac-n-Cheese:~ nicolas$ echo "(2/3)+(7/8)" | bc -l
1.54166666666666666666

Another way to do floating point arithmetic is to use AWK:

Mac-n-Cheese:~ nicolas$ awk "BEGIN {print 100/3}"
33.3333

You can use printf to adjust the precision of the results:

Mac-n-Cheese:~ nicolas$ awk "BEGIN {printf \"%.2f\n\", 100/3}"
33.33

When using negative values, make sure to leave a white space between signs.

Mac-n-Cheese:~ nicolas$ awk "BEGIN {print -8.4 - -8}"
-0.4