Inside the shell to determine if the string is empty

There are several main ways to do this:

echo "$str" |awk ' {print length ($)} '
Expr Length "$str"
echo "$str" |wc-c
But the third one will be 1 more, maybe the terminator is counted.

There are three ways to determine that a string is empty:
If ["$str" = ""]
If [x "$str" = x]
If [-Z "$STR"] (-n is not null)
Note: You must substitute double quotes, otherwise some commands will complain, develop good habits.

I just always forget to add double quotes, I am really a beginner ...

Original Address http://im00100.blog.163.com/blog/static/76046672008091113817/