Improve command substitution

- .kshrc file isn't special - $ENV can point to any file
- use $MAIL since is available by default
- replace backticks ('`') with '$()' - they both nest and look better
- be consistent about using `[` or `test` - chose the latter here
- use `-n` for the second test case in order to keep the examples'
  logic the same:

	[...] && echo '* '

1 files changed, 4 insertions, 4 deletions

diff --git a/pages/unixtips.md b/pages/unixtips.md
index 3087c04..84b74ad 100644
--- a/pages/unixtips.md
+++ b/pages/unixtips.md
@@ -11,7 +11,7 @@ them up on this shell. So here are some things I do on my local machine
 that work here:
 
 To get the shell to tell you when you have new mail, after command
-executions, add this to your `.profile` or your `.kshrc` files 
+executions, add this to your `.profile` or your `$ENV` files 
 (or other shell RC file) in your home directory.
 
 ```
@@ -20,16 +20,16 @@ export MAILCHECK=0
 
 And, if you want, you can have a persistent notification when
 you have un-incorporated mail, or more specifically, when your
-`/var/mail/<username>` isn't empty.
+`$MAIL` (`/var/mail/$USER` by default)` isn't empty.
 
 ```
-PS1="$([ -s /var/mail/`whoami` ] && echo '* ')$PS1"
+PS1="$(test -s $MAIL ] && echo '* ')$PS1"
 ```
 
 For maildir try this:
 
 ```
-PS1="$(test -z "`ls -A $HOME/Maildir/new`" || echo '* ')$PS1"
+PS1="$(test -n "$(ls -A $HOME/Maildir/new)" && echo '* ')$PS1"
 ```
 
 This works in `/bin/ksh`, I can't speak for other shells.