Printing evaluated prompt placeholders to screen

Question

Is there a way to print interpreted PS1 variable placeholders to console? Something like

$ echo `%u`

for printing a username or

$ echo `%h`

for printing a host. I do know about environment variables I just want to know if there is a way to get same information through PS1 variable.

Answer 1

In zsh, use the % parameter expansion flag.

tmp='%n@%m'; echo ${(%)tmp}

In bash, there doesn't seem to be an easy way, but there's a sneaky way:

tmp=$(set +x; (PS4='+.\u@\h'; set -x; :) 2>&1); tmp=${tmp#*.}; echo ${tmp%:}

In tcsh, I don't think there's a way. (But who uses (t)csh these days anyway?)