80 lines
1.9 KiB
Bash
80 lines
1.9 KiB
Bash
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# Working with numbers in bash
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Bash interprets everything by default as a string, however it can also work with
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numbers, just be careful with your conditional operators
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## Storing numbers
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`declare` and `local` both can make integer variables with the `-i` flag
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```bash
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declare -i a=2
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f () { local -i a=3 ;}
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```
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Variables can be manipulated in double parenthesis, very similar to c/python.
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Use `$(())` to return the value instead. Edges and centers seem whitespace
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insensitive. No need to `$` in front of variables inside `(())`
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Work as expected: `+ - * %`
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Exponent: `**`
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Floored division: `/`
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```bash
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declare -i a=2 b=3 # Multiple on the same line are fine
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(( a++ )) # a == 3
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(( a+=b )) # a == 6
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(( a = 2 )) # a == 2
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((a=4+b)) # a == 7
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(( a = 4 + b )) # Spacing is optional, same as above
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declare -i c=$((a**b + 4)) # c == 7**3 + 4 == 347
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```
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## Using numbers
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Conditionals are different for numbers in bash. Mapping c to bash:
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```
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C | Bash
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----|-----
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== | -eq
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!= | -ne
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> | -gt
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< | -lt
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>= | -ge
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<= | -le
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```
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```bash
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declare -i a=3 b=2
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if [[ $((a**b)) -ge 1000 ]]; then
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echo "Exponentiation with ${a}^${b} is pretty big"
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elif [[ $a -lt $b ]]; then
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echo "$a is smaller than $b"
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else
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echo "$a isn't smaller than $b"
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fi
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echo "You rolled a: $(( RANDOM % 6 + 1 )) on a 6 sided dice"
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```
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## Floats
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Bash has no support for floats, don't even try. If you need floats, use awk,
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which has full support. To still sort of use rational numbers in bash, store a
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numerator and denominator, then pass both to awk when you need the float
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```bash
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declare -i num_1=4 denom_1=9
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declare -i num_2=2 denom_2=9
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(( num_1 += num_2 ))
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awk -v n1=$num_1 -v d1=$denom_1 -v n2=$num_2 -v d2=$denom_2 \
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'BEGIN { printf "%.2f\n", n1/d1 + n2/d2 }'
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```
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Bash has floored division `/` and remainders `%`, though the awk approach is
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easier. Note awk's syntax is identical to c, so it uses `^` for exponentiation
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and the standard `==`, `<=`... for comparison
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