标签：sh变量特性
echo ${#A}
结果：12A='Hello world!'
echo ${A:-OK}
结果：Hello wold!
unset A或 A=’’
echo ${A:-OK}
结果：OKA='Hello world!'
echo ${A:+OK}
结果：OK
unset A 或A=’’
echo ${A:+OK}
结果：A='Hello world!'
echo ${A:=OK}
结果：Hello world!
unset A 或A=’’
echo ${A:=OK}
结果：OK
echo $A
结果：OKA='Hello world!'
echo ${A:3}
结果：Hello world!A='Hello world!'
echo ${A:3:4}
结果：Hello world!标签：sh变量特性
原文地址：http://blog.51cto.com/lythjq/2073516
