Practice exercise in Bash Basics Series #4: Arithmetic Operations

Bash Basics Series
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If you are following the Bash Basics series on It’s FOSS, you can submit and discuss the answers to the exercise at the end of the chapter:

Fellow experienced members are encouraged to provide their feedback to new members.

Do note that there could be more than one answer to a given problem.

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@abhishek ,
That link does not work

It says… itsfoss.com host error

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Must have been a temporary glitch? Worked for me this morning, still works…

Note also - a few years back, I started a thread about doing maths in the shell :

Anyway - I’d only just started learning how to use awk to do floating point arithmetic (in preference to using “bc”) - and when I saw this new thread, I went looking for some older shell scripts I might have written using awk to do floats, and couldn’t find a single example!

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Should be temporary but do let me know if it persists :hourglass_flowing_sand:

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9 posts were split to a new topic: It’s FOSS website returns server error 520

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About the ((...)) notation, it should be noted that:

  1. We can omit $ for variables in any arithmetic expression.
    For example, we can write res=$((var1 + var2)) instead of res=$(($var1 + $var2))
    As this rules applies for any arithmetic expression, not only within ((...)). For example, the following are valid:
    • i=3; str="abcdefgh"; echo ${str:i:i+1} (will be evaluated as echo ${str:3:4})
    • declare -i i=3; i=i+2; i+=5 (i value is 10)
  2. the assignments operators (=, +=, <<=, ^= etc…) are valid in ((...)) construction. We can write ((res = var1 + var2)) instead res=$((var1 + var2))
  3. ((...)) can be nested. ((i = 2 + ((j = 4 * 10)))) will give i=42 and j=40.
  4. I think you should give the full list of arithmetic operators, including comma, assignment, comparison, logical, bitwise and expr?expr:expr. They allow to have complex arithmetic expressions, such as ((i=3, j=4, k=i>j? i:j)) (k will be the max of i and j).
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Thanks for the additional inputs.

I should add the first 3,

About the 4th one, logical operators and bitwise operators will be covered separately.

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If you add the first 3, maybe you could also consider to include <</>> (and <<=/>>=) operators, as they are actually a multiplication/division by a power of 2: (( i <<= p )) is (( i *= ( 2 ** p ) )) and (( i >>= p )) is (( i /= ( 2 ** p ) )).
And also add an important warning on overflow, when we try to calculate over LONG_MAX and under LONG_MIN (defined in /usr/include/limits.h).
For example, on my system, LONG_MAX is 9223372036854775807, and we have an overflow with echo $((9223372036854775807 + 1)). bc (or my favorite dc) would be preferable in these cases, when numbers may go high/low.