问题
When I set my PS1='$PWD' the command line shows me the path to the current directory:
/home/myname and it changes when I change the directory.
But when I change it to "$PWD" ( double quotes ) it always shows me the /home/myname no matter where I am at the moment. From what I've read it says that single quotes prints exactly what it is in it and don't expand special symbols like $. So why is it working that way?
回答1:
The "$PWD" resolves immediately. So you're essentially setting PS1 to a fixed value (the value of PWD at the time it's set). When you set to '$PWD', it does not resolve immediately, so it resolves when used, and changes when you change directories. Thus the double quotes are expanding (to a fixed string) as expected, while single quotes are not.
回答2:
PS1 is a special variable. From the ksh man page:
PS1 The value of this variable is expanded for parameter expansion,
command substitution, and arithmetic substitution to define the
primary prompt string which by default is ``$''. [...]
So, the value of PS1 gets special treatment before the prompt is displayed. When using single quotes, the value of PS1 is merely the string $PWD but when a prompt is required, ksh will further expands variables so the prompt gets your current directory.
来源：https://stackoverflow.com/questions/16902814/single-double-quotes-ksh