Hi,

I am learning shell scripting for the first time. I use AT&T Korn Shell, Version AJM 93u+ 2012-08-01, compiled from source on NetBSD.

So far I have managed to set up what I think is a useful and pleasing shell prompt, which can be seen in the image attached to this post.

The prompt is a multi-line prompt, as follows:

Line 1 (reverse video) shows the TERM variable, together with TTY, SHELL, and the date and time as it was when the prompt was updated.
(The print -f statement formats this line so that the text is right-aligned and the reverse-video bar takes up the whole width of the terminal, even if it is resized. It uses the COLUMNS variable to achieve this.)

Line 2 shows the host I am connected to (obscured for security).

Line 3 shows the job number and current working directory.

Line 4 shows the user name and the prompt itself.

I have just one problem: unless I symlink /bin/ksh93 to /bin/sh (the default shell on NetBSD) I get errors about "bad substitution". I am certain my prompt is causing this problem, but I still don't know enough to say what is wrong. Would somebody be so kind as to look at my PS1 and tell me where I am going wrong, and where I can improve it? I have learned quite a bit about if...then and case statements while learning how to do this prompt, but I am still unclear about brackets, single quotes and double quotes.

The following is the relevant part of my .kshrc file. I have split the PS1 lines for readability but they are all on one line in the file.

Code:

                                                                         
ttyhere=$(tty | sed -e "s:/dev/::")                                               
timenow=$(date +"%H:%M %Y%m%d")                                                   
currshell=$(print "$SHELL" | sed -e "s:/bin/::")                                  
                                                                                  
PS1='$(print -f "\n\E[1;7m%${COLUMNS}s\E[0m\n" "[$TERM] \
[$ttyhere] [$currshell] [Time at prompt: $timenow] "; \
print "[$(hostname)]"; \
print -n "[\E[1;36m!\E[0m]"; \
if [[ "${PWD#$HOME}" != "$PWD" ]] then; \
print "[\E[1;35m~${PWD#$HOME}\E[0m]"; \
else; print "[\E[1;35m$PWD\E[0m]"; fi; \
if [[ $(id -u) -ne 0 ]] then; \
print "[\E[1;36m$(id -un)\E[0m]$ "; \
else; print "[\E[1;35m$(id -un)\E[0m]# "; \
fi;)' ;;