How to save a path with ~ into a variable?

Question

I have these variables in my script:

TARGET=username
TARGET_DIR="~${TARGET}/.ssh"

I want the TARGET_DIR var to hold this path: /home/username/.ssh but to use ~ instead of /home/. But when I run the script and try to make new .ssh dir under username it tells me:

mkdir: cannot create directory ‘~username/.ssh’: No such file or directory

Even though the /home/username dirs exists. If I do: TARGET_DIR="/home/${TARGET}/.ssh" it works. How can I use the ~ sign in the variable?

Answer 1

In bash, ash, mksh and yash tilde expansion occurs before parameter expansion, so that can't work.

You can use ksh93 or zsh instead here, or resort to eval:

user=username # making sure it's a valid username
eval "user_home=~$user"
target_dir=$user_home/.ssh

If your system has a getent command (quite common nowadays), you can also use:

user_home=$(getent -- passwd "$user" | cut -d: -f6)

Or use perl:

user_home=$(perl -le 'for (@ARGV) {
  @u = getpwnam$_ or die "No such user: $_\n";
  print $u[7]}' -- "$user")

Which would also work with users with uncommon characters in their username (like space which zsh's ~$user but not ksh93's ~"$user" would also have a problem with).