Re: shells (was Re: Zoom.)

From	rhkramer@gmail.com
Newsgroups	linux.debian.user
Subject	Re: shells (was Re: Zoom.)
Date	2020-10-20 17:00 +0200
Message-ID	<B21hf-1Rm-3@gated-at.bofh.it> (permalink)
References	<B11CF-6Tb-1@gated-at.bofh.it> <B1XdE-7VW-7@gated-at.bofh.it> <B1Y9I-8vu-15@gated-at.bofh.it>
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Top posting intentionally as I don't think any (or much) context is required.

I am always impressed with Greg's knowledge of the Bash shell (maybe all 
shells), but, wow, Bash seems like a convoluted mess to keep track of all the 
little details / gotchas.

Is there a shell that is better in that respect?  Maybe the c-shell?  I don't 
like c (because I have a hard time programming in it), but if the c-shell has 
less intricacies (and is quite consistent with the c language), then maybe 
(for me) it is worth switching to (someday ;-)

Nothing new below this line.

On Tuesday, October 20, 2020 07:36:39 AM Greg Wooledge wrote:
> The weird backslashing tells me you're defining PS1 with double quotes
> instead of single quotes, which is weird, and probably indicates that
> you're doing even worse things, like dynamically generating pieces of
> your PS1... I've seen things... things that no man should see....
> 
> Anyway, in addition to the weird quoting and possible abominations
> unrevealed, your command substitution forks.  Every time the prompt
> is drawn, a new process is forked, just to do that simple "if" check.
> 
> The standard workaround for that is to use an array variable with the
> two possible outcomes, and a bit of arithmetic.
> 
> unicorn:~$ green=$(tput setaf 2) red=$(tput setaf 1) normal=$(tput sgr0)
> unicorn:~$ status=(+ -) statcolor=("$green" "$red")
> unicorn:~$ PS1='\[${statcolor[!!$?]}\]${status[!!$?]}\[$normal\] \h:\w\$ '
> + unicorn:~$ true
> + unicorn:~$ false
> - unicorn:~$ true
> + unicorn:~$
> 
> (You can't see the colors in the mailing list, but they're there.)
> 
> Just remember the basics:
> 
> 1) Use single quotes around your definition of PS1, because you want all
>    of the parts of it to be taken literally, and quoting is already hard
>    enough without making it worse.
> 
> 2) Variable expansions are "free" (do not cost a process fork).  This
>    includes variables that are set by PRMOPT_COMMAND, which is the more
>    efficient way to set variables dynamically if you *really* need that,
>    which you probably don't.
> 
> 3) Color and other terminal escape codes can and should be stored in
>    variables, which you can expand in PS1, as long as the PS1 definition
>    is single-quoted.  Don't store raw terminal sequences, because they
>    are not the same for all terminals.  This is what tput(1) is for.
> 
> 4) Terminal escape sequences that don't change the cursor position should
>    be enclosed in \[ \] so the shell knows where the cursor is at all
>    times.
> 
> 5) When expanding the index of an indexed array variable, the square
>    brackets are a math context.  In a math context, !!$? means "negate
>    the previous command's exit status twice".  So, 0 -> 1 -> 0, or
>    nonzero -> 0 -> 1.  Thus, !!$? always expands to either 0 or 1.  And
>    because it's in single quotes, it shouldn't trip history expansion,
>    if you still have history expansion turned on.  (I don't.)

Thread

Zoom. peter@easthope.ca - 2020-10-17 23:10 +0200
  Re: Zoom. Charles Curley <charlescurley@charlescurley.com> - 2020-10-17 23:40 +0200
  Re: Zoom. Peter Ehlert <peter@sdi-baja.com> - 2020-10-18 00:10 +0200
  Re: Zoom. Carl Fink <carlf@panix.com> - 2020-10-18 01:00 +0200
    Re: Zoom. conover@rahul.net (John Conover) - 2020-10-18 01:40 +0200
  Re: Zoom. David <bouncingcats@gmail.com> - 2020-10-18 01:50 +0200
    Re: Zoom. riveravaldez <riveravaldezmail@gmail.com> - 2020-10-18 05:10 +0200
    Re: Zoom. Tom Dial <tddial@comcast.net> - 2020-10-18 09:20 +0200
  Re: Zoom. Bob McGowan <ramjr0915@gmail.com> - 2020-10-18 03:30 +0200
    Re: Zoom. peter@easthope.ca - 2020-10-19 23:10 +0200
      Re: Zoom. Michael Stone <mstone@debian.org> - 2020-10-19 23:10 +0200
        Re: Zoom. peter@easthope.ca - 2020-10-22 15:30 +0200
          Re: Zoom. Michael Stone <mstone@debian.org> - 2020-10-22 16:40 +0200
      Re: Zoom. John Crawley <john@bunsenlabs.org> - 2020-10-20 04:30 +0200
        Re: Zoom. Dan Ritter <dsr@randomstring.org> - 2020-10-20 12:40 +0200
          Re: Zoom. Nicolas George <george@nsup.org> - 2020-10-20 13:20 +0200
          Re: Zoom. Greg Wooledge <wooledg@eeg.ccf.org> - 2020-10-20 13:40 +0200
            Re: Zoom. Dan Ritter <dsr@randomstring.org> - 2020-10-20 14:10 +0200
            Re: shells (was Re: Zoom.) rhkramer@gmail.com - 2020-10-20 17:00 +0200
              Re: shells (was Re: Zoom.) Nicolas George <george@nsup.org> - 2020-10-20 17:00 +0200
              Re: shells (was Re: Zoom.) Tony van der Hoff <lists@vanderhoff.org> - 2020-10-20 17:40 +0200
  Re: Zoom. A_Man_Without_Clue <love.chaser@gmail.com> - 2020-10-18 05:20 +0200
  Re: Zoom. Stefan Monnier <monnier@iro.umontreal.ca> - 2020-10-18 17:20 +0200
    Re: Zoom. Sven Hartge <sven@svenhartge.de> - 2020-10-18 17:50 +0200
      Re: Zoom. <tomas@tuxteam.de> - 2020-10-19 09:30 +0200
        Re: Zoom. Sven Hartge <sven@svenhartge.de> - 2020-10-19 09:40 +0200
          Re: Zoom. David Wright <deblis@lionunicorn.co.uk> - 2020-10-19 17:10 +0200
          Re: Zoom. Stefan Monnier <monnier@iro.umontreal.ca> - 2020-10-19 17:30 +0200
            Re: Zoom. <tomas@tuxteam.de> - 2020-10-19 17:40 +0200
            Re: Zoom. Stefan Monnier <monnier@iro.umontreal.ca> - 2020-10-19 18:00 +0200
          Re: Zoom. Stefan Monnier <monnier@iro.umontreal.ca> - 2020-10-19 17:40 +0200
        Re: Zoom. "Thomas Schmitt" <scdbackup@gmx.net> - 2020-10-19 10:00 +0200
    Re: Zoom. peter@easthope.ca - 2020-10-20 03:20 +0200
      Re: Zoom. <tomas@tuxteam.de> - 2020-10-20 10:10 +0200
    Re: Zoom. peter@easthope.ca - 2020-10-20 03:30 +0200
    Server for Jitsi; was: Zoom. peter@easthope.ca - 2020-10-22 20:20 +0200
      Re: Server for Jitsi; was: Zoom. Dan Ritter <dsr@randomstring.org> - 2020-10-22 20:40 +0200
      Re: Server for Jitsi; was: Zoom. "der.hans" <deb-user@LuftHans.com> - 2020-10-22 21:00 +0200
      Re: Server for Jitsi; was: Zoom. Stefan Monnier <monnier@iro.umontreal.ca> - 2020-10-23 01:40 +0200

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