The difference between if -n and -z in shell

if [ str1 = str2 ]　　　　　 When two strings have the same content 、 Length is true
if [ str1 != str2 ]　　　　　 Dangchuang str1 and str2 It's true when you don't wait
if [ -n str1 ]　　　　　　 When the length of the string is greater than 0 Time is true ( The string is not empty )
if [ -z str1 ]　　　　　　　 When the length of the string is 0 Time is true ( Empty string )
if [ str1 ]　　　　　　　　 Dangchuang str1 If it's not empty, it's true