RFC - Korn shell prompt


 
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# 1  
Old 06-14-2014
RFC - Korn shell prompt

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;)' ;;

RFC - Korn shell prompt-promptpng

Last edited by gezley; 06-14-2014 at 03:22 AM.. Reason: Formatting
# 2  
Old 06-14-2014
Quote:
Originally Posted by gezley
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;)' ;;

Attachment 5787
Try changing to:
Code:
ttyhere=$(tty)
ttyhere=${ttyhere##*/}                                               
timenow=$(date +"%H:%M %Y%m%d")                                                   
currshell=${SHELL##*/}                                  
                                                                                  
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)'

The main problem was the missing ; between ]] and then in two places in your if statements.

You have some other ;s that aren't needed, but they wouldn't keep your script from working.

You can use [ expression ] instead of [[ expression ]] with the expressions you're using, but either will work with a 1993 or later version of ksh.

The changes to ttyhere and currshell are just performance improvements.

Keep the ;; I removed at the end of this if it is code that has been extracted from the end of a choice in a case statement; otherwise, it is likely to be a syntax error.
This User Gave Thanks to Don Cragun For This Post:
# 3  
Old 06-14-2014
Quote:
Originally Posted by Don Cragun
Try changing to:
Code:
ttyhere=$(tty)
ttyhere=${ttyhere##*/}                                               
timenow=$(date +"%H:%M %Y%m%d")                                                   
currshell=${SHELL##*/}                                  
                                                                                  
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)'

The main problem was the missing ; between ]] and then in two places in your if statements.
Thank you Don! I am hugely embarrassed to tell you that it now turns out my "bad substitution" problem was down to a bad alias. When I substituted your prompt for mine I still had the error, so I looked more closely at the rest of my .kshrc and .profile and commented out bit by bit till I narrowed it down to the following rogue statement, which is meant to return the version of ksh I am running:
Code:
alias kv="print ${.sh.version}"

Dear oh dear. So sorry! But I am happy you've cleaned up my prompt. I'm now going to go off and figure out what you did with my TTY and SHELL variables.
Quote:
You have some other ;s that aren't needed, but they wouldn't keep your script from working.
This one has me perplexed. I've looked through the prompt and can't really put my finger on the ;s which could be removed. Edit: I see them now, after the else keywords and fi.
Quote:
You can use [ expression ] instead of [[ expression ]] with the expressions you're using, but either will work with a 1993 or later version of ksh.
Done.
Quote:
Keep the ;; I removed at the end of this if it is code that has been extracted from the end of a choice in a case statement; otherwise, it is likely to be a syntax error.
haha! Well spotted. Indeed I do have a case statement, which accommodates Emacs: when I open a shell inside emacs TERM is reported as "dumb", and the first line of the prompt is slightly different, so I just use this case statement to fix the issue that arises. A learning exercise for me really.
Once again, thank you so much for taking the time to fix this for me! Now off for more learning!

Smilie

Last edited by gezley; 06-14-2014 at 07:29 PM..
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