Shell Programming and Scripting

I am not really sure what you mean by that, but first let us be precise: are you talking about ksh88 (as it is found as the default shell in AIX and HP-UX) or ksh93?

Second, as far as i know there is no "history buffer" - apart from the history file - in ksh. You can have a separate history file for each shell instance (actually i like it that way because usually i need in a certain session the commands i used there before again, not the ones i used elsewhere, but that is a matter of personal taste) or you can have all sessions share a common history file. In each case "history" in the Korn shell is what is in this history file, nothing more, nothing less.

I hope this helps.

bakunin

Hi, bakunin. I'm finding that it is not so simple. If I have ksh running in a terminal emulator and manually edit the history file while the emulator is running, lines that I add to the HISTFILE will be picked up by the emulator. However, lines that I delete from the HISTFILE continue to show up in the terminal emulator's history. So it seems that the shell's idea of the history (which I'm calling its "history buffer") and what's actually in the HISTFILE are two different things. The only way for deleted lines to stop showing is to close the terminal emulator and open a new one.

Maybe my terminal emulator is introducing some unexpected behavior? I'll try a different emulator.

Thank you Jim and Neo. Yes, I'm finding that the only way to understand exactly what's going on will be to look at the source code. Alas, while my sh/bash, python, and perl kung fu is strong, C/C++ looks like gibberish to me, but I'll give it a shot anyway. If switching terminal emulators and/or recompiling ksh don't give me exactly the behavior I want, I may just go back to bash, which feels much more comfortable.

P.S. I'm using the public domain korn shell v5.2.14 (the default shell in OpenBSD 6.4).

Well, pdksh is famous for being barely compatible with any real ksh, so i'd like to put what i said above in perspective: it was meant about "real" ksh-versions, mainly about ksh88 as found in AIX and ksh93 as found in AIX and Linux. The (real, AST) Korn shell was made open source IIRC 2005, so there is IMHO no reason to work with rather inept look-alikes (or, rather, look-similars) like the pdksh at all. Drop it and get a real Korn shell from github or kornshell.com.

I hope this helps.

bakunin

I recommend you open the C/C++ source code in a modern code editor, and having said that, I strongly recommend Visual Studio Code with the CPP extension:

C++ programming with Visual Studio Code

VSC also has extensions to prettify (format, beautify), indent, and to color matching brackets, braces and parens so all of this "cool stuff" makes code easier to read (and colorful, LOL)

Having the IntelliSense for CPP will help you understand the code. I write mostly in Javascript, PHP, CSS and HTML these days (nearly every day). VSC saves me a lot of time debugging syntax and keeping things moving along in a brisk development pace.

Thanks, bakunin. I'm new to the Korn shell, so had no idea about these nuances. I see that ksh93 is in the OpenBSD package repository, so I'll install it and see how it's different from pdksh.

Neo, I will give VSC/IntelliSense a try. If it makes CPP easier to read and work with, I will probably really like it.

In the meantime, I'm back to bash for when I want to work and not play/explore. I find that having this in my .bashrc gives me exactly the behavior I expect (namely, any time I press Enter in a terminal, the shell's idea of the history matches exactly what is in my HISTFILE--no more, no less):

Code:

PROMPT_COMMAND="history -a; history -c; history -r"

Thank you all very much. Happy hacking!

OK, i might be a bit slow but now i get what you want. If this is what you want you can have that in ksh too. There is no PROMPT_COMMAND variable in ksh but the shell prompt itself is capable of executing commands:

Code:

PS1='$(command; command; command; ...) <rest of your prompt here>'

Notice that editing the commad history needs the variable HISTEDIT (in ksh93) or FCEDIT (in ksh88) to be set to your preferred editor, otherwise you end up in ed. The history comamnd in ksh is hist, which by default is aliased to fc and r (for "repeat"). You can search and replace when repeating commands like this:

Code:

r old=new x

which will re-run the last command line starting with "x" but the instances of "old" replaced with "new".

I hope this helps.

bakunin

I had tried that, but apparently pdksh there is no history command: 'history' is just an alias for 'fc -l'

So you're saying the "real" ksh has 'history' command with these flags? Nice! I'm sorry about the ksh version mixup. It's tough being a noob!