2-2 shell字符串处理

计算字符串长度

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var5="/usr/local/Cellar/dart/2.5.2/bin:/Users/lihe/Downloads/flutter/bin"
echo ${#var5}

输出结果 66

var5="/usr/local/Cellar/dart/2.5.2/bin:/Users/lihe/Downloads/flutter/bin"
var6=`expr  ${#var5}`
echo $var6

输出结果 66

提取字符串

1 ${字符串变量:提取位置:提取长度}

var1="i love you, do you love me"
var2=${var1:2:10}
echo $var2

输出结果
love you,

2 ${字符串变量:提取位置} 从index开始提取到最后

var1="i love you, do you love me"
var2=${var1:2}
echo $var2

输出结果
love you, do you love me

3 ${字符串变量:-提取位置} 从最后面的index开始向前提取

var1="i love you, do you love me"
var2=${var1:-2}
echo $var2

输出结果
i love you, do you love me