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shell编程
shell编程
Shell 脚本中的数学运算
bash shell 的基础运算主要有4种形式：
- $(( expression ))
- $[ expression ]
- expr operation
- 使用 let
实例：
#!/bin/bash
set -e
set -u
a=20
echo "a = $a"
b=6
echo "b = $b"
c=4.5
echo "c = $c"
result=$(( a + b ))
echo "The result of '\$(( a + b ))' is $result"
result1=$[ a - b ]
echo "The result of '\$[ a - b ]' is $result1"
result2=`expr $a \* $b`
echo "The result of '\`expr \$a \* \$b\`' is $result2"
let "result3 = $a + $b"
echo "The result of 'let \"result3 = \$a + \$b\"' (result3) is $result3"
result4=$(expr $a / $b )
echo "The result of '\$(expr \$a / \$b )' is $result4"
result5=$(( a + c ))
结果：
#!/bin/bash
set -e
set -u
a=20
echo "a = $a"
b=6
echo "b = $b"
c=4.5
echo "c = $c"
result=$(( a + b ))
echo "The result of '\$(( a + b ))' is $result"
result1=$[ a - b ]
echo "The result of '\$[ a - b ]' is $result1"
result2=`expr $a \* $b`
echo "The result of '\`expr \$a \* \$b\`' is $result2"
let "result3 = $a + $b"
echo "The result of 'let \"result3 = \$a + \$b\"' (result3) is $result3"
result4=$(expr $a / $b )
echo "The result of '\$(expr \$a / \$b )' is $result4"
result5=$(( a + c ))
推荐涉及运算，统一使用,方便区分
$[ expression ]
