运算符

加减乘除取余  expr
例:
a=1
b=2
c=`expr $a + $b`
echo $c
结果:
3
同时说明:
加减乘除还可以写为:
$(expr $a+$b)
或
$[$a+$b]
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注意乘法需要转义\*
例:
a=2
b=2
c=`expr $a \* $b`
echo $c
结果:
4

剩下以此类推
+-*/%
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赋值运算 =
a=9
b=$a
echo $b
结果:
9
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运算符 ==
a=2
b=2
if [$a == $b]
then
echo "a等于b"
else
echo "a不等于b"
fi

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运算符 !=
a=2
b=2
if [$a != $b]
then
echo "a等于b"
else
echo "a不等于b"
fi
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-o  或运算符
a=2
b=2
if [$a -lt 10 -o $b -gt 20]
then
echo "结果成立"
fi
注解: -lt 和 -gt 请参考预算法列表

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-a 与运算符相当于  && 或 and  与运算
a=2
b=2
if [$a -lt 10 -a $b -gt 20]
then
echo "成立"
else
echo "不成立"
fi
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&&与运算符  逻辑且
a=2
b=2
if [[ $a -lt 10 && $b -gt 20 ]]
then
echo "成立"
else
echo "不成立"
fi
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||与运算符  逻辑或
a=2
b=2
if [[ $a -lt 100 || $b -gt 200 ]]
then
echo "成立"
else
echo "不成立"
fi
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= 判断是否相等
a=2
b=2
if [ $a = $b ]
then
echo "相等"
else
echo "不相等"
fi
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!= 判断是否相等(不等与)
a=2
b=2
if [ $a = $b ]
then
echo "相等"
else
echo "不相等"
fi
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-z 判断字符串长度是否为0
a=2
if [ -z $a ]
then
echo "长度为0"
else
echo "长度不为0"
fi
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-n 判断字符串长度是否为0  和-z刚好相反
a=2
if [ -n $a ]
then
echo "长度不为0"
else
echo "长度为0"
fi
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校验字符串是否为空
a=2
if [$a]
then
echo "长度为空"
else
echo "长度不为空"
fi

附录:

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