Well, I'll abstain from diving into your code; you're right, it's quite ugly.
:-)
For the date calculations part of your question the easiest may be to use some
builtins.
The following create the current date and the date "t0" from the current day,
both in seconds...
t_now_s=$( printf "%(%s)T\n" )
t0_s=$( printf "%(%s)T\n" "$(date +%Y)" )
seconds_diff=$(( t_now_s - t0_s ))
(Maybe it's even easier than that to achieve, but I think this is already more
legible then what you have.)
Subject: Re: [ast-users] how to get functionality of bash compatible PS1
without rest of bash compatibility?
From: rlham...@gmail.com
Date: Thu, 12 Mar 2015 17:26:58 -0400
CC: ast-users@lists.research.att.com
To: janis_papanag...@hotmail.com
My code does NOT attempt to provide bash PS1 compatibility, it just plugs in a
time and truncated (leading levels) directory; the time is based on a computed
offset since midnight to add to SECONDS, so it doesn’t need to run builtins
when PS1 is evaluated. It works, and the performance isn’t horrible, but it’s
ugly beyond all recognition.
Some of it’s mine, some of it (the directory part for sure; can’t remember
whether the start of the time code was mine or a scrounge) is scrounged.
Basically I make a PS0 that will later (within function _cd) become part of PS1.
Before, I actually reset SECONDS to be seconds since midnight, but I recently
changed it to be an offset added to SECONDS, so as to leave SECONDS unaltered
and be able to stick it in PS4 along with a set -x at the top of my .profile,
trying to track down an annoying variation from < 1 sec to > 10 sec in how long
it takes to start a new login shell.
cd is aliased to function _cd, which runs real ‘cd’ and diddles the path part
of PS1.
Here’s the PS0 (time) part: eval export _offset="$(( $(/bin/date
'+3600*%H+60*%M+%S') - ${SECONDS} ))" _pad[1]=0;_pad[2]=''
_hh="((SECONDS+${_offset})/3600)%24" _mm="((SECONDS+${_offset})/60)%60"
_ss="((SECONDS+${_offset}))%60"
_time='${_x[(_m=_mm)==(_h=_hh)==(_s=_ss)]}${_pad[${#_h}]}$_h:${_pad[${#_m}]}$_m:${_pad[${#_s}]}$_s'
PS0="$_time[!]${_hostname%%.*}:"
Like I said, I don’t even really understand the line starting with _time=
anymore. The _pad[] part I understand, but not the _x[] part, although I think
that might have been a way to cause the evaluation to happen as I needed it to.
Within _cd, PS1 finally gets set as follows: if (( ${#PWD} > 15 ))
then t1="${PWD%/*???????????????}" t2="${PWD#$t1/}"
if (( ${#PWD} > ( ${#t2} + 3 ) )) then
PS1="${label}$PS0...${t2}${p} " else
PS1="${label}$PS0$PWD${p} " fi else
PS1="${label}$PS0$PWD${p} " fi
$label is (depending on the terminal type) an escape sequence to incorporate
the hostname and current directory into the window title bar. To keep that
from confusing ksh’s idea of display column, it ends with a ^M.
It all works, but the ugliness is OTT. There’s got to be a better way…
On Mar 12, 2015, at 8:51 AM, Janis Papanagnou <janis_papanag...@hotmail.com>
wrote:To understand your situation...
You have already functional code?
Your code works but it has a performance problem building the PS1 prompt?
If you want something "cleaner" and "faster" it would help if you post your
code so that we see where you are.
> From: rlham...@gmail.com
> Date: Thu, 12 Mar 2015 08:20:42 -0400
> To: ast-users@lists.research.att.com
> Subject: [ast-users] how to get functionality of bash compatible PS1 without
> rest of bash compatibility?
>
> Yep, that was the question: more or less bash-compatible PS1 handling without
> the rest of bash compatibility. I like timestamps and other odd things
> (shortened directory) in my prompt, but I’d rather do it without enabling any
> more bash compatibility than that. I’ve got some odd code that even I no
> longer understand that gives the output I want, but it’s very ugly (certainly
> not using a get discipline or anything like that, but computing a date having
> determined an offset to apply to SECONDS to count since midnight). Something
> cleaner and faster might be nice.
>
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