sh变量特性（2）

echo ${#A}

A='Hello world!'

echo ${A:-OK}

结果：Hello wold!

unset A或 A=’’

echo ${A:-OK}

A='Hello world!'

echo ${A:+OK}

结果：OK

unset A 或A=’’

echo ${A:+OK}

A='Hello world!'

echo ${A:=OK}

结果：Hello world!

unset A 或A=’’

echo ${A:=OK}

结果：OK

echo $A

A='Hello world!'

echo ${A:3}

A='Hello world!'

echo ${A:3:4}

sh变量特性（2）

原文：http://blog.51cto.com/lythjq/2073516