总结在Linux终端中进行算数运算的6种方式

echo $((1+20))
a=$((2*4))
echo $a
b=$(($a-3))
echo $b
d=$(($b/2))
echo $d
e=$(($a%5))
echo $e

let a=1+2
echo $a
let b=$a*3
echo $b
let c=$b/4
echo $c

expr 3 + 5
expr 15 % 3
expr 5 \* 3 
expr 5 - 3
expr 20 / 4
NUM=$(( 1 + 2))
echo $NUM
NUM=$(expr $NUM + 2)
echo $NUM

expr 5 = 3
expr 5 = 5
expr 8 != 5
expr 8 \> 5
expr 8 \< 5
expr 8 \<= 5

expr length "hello world!"
#等效于
echo "hello world!" | wc -L

echo '3+4' | bc
echo '3*4' | bc
echo '33/4' | bc
echo '32%6' | bc
echo '33/6' | bc -l

awk 'BEGIN { a = 10; b = 3; print "(a + b) = ", (a + b) }'
awk 'BEGIN { a = 10; b = 3; print "(a - b) = ", (a - b) }'
awk 'BEGIN { a = 10; b = 3; print "(a *  b) = ", (a * b) }'
awk 'BEGIN { a = 10; b = 3; print "(a / b) = ", (a / b) }'
awk 'BEGIN { a = 10; b = 3; print "(a % b) = ", (a % b) }'

factor 21
factor 242
factor 2123
factor 200