1, test operation symbols all strings must be enclosed in double quotes;
2, both ends must be a space symbol comparison;
Common string test operators
the -Z "String" If the string length is zero True 0
-n "string" If the length is not 0 True no zero
"String 1" = "String 2" if the string is equal to 1 True 2 strings, can be used instead of = ==
"String 1"! = "String 2" if the string is not equal to 1 True 2 strings, not! == instead of! =
