Execute a Command in PS1 w/o Disturbing Previous Return Value?

Execute a Command in PS1 w/o Disturbing Previous Return Value?

[Aaron Davies]

I'm trying to write a prompt that will do two things: include a file 
frequently re-downloaded from the web, and indicate the return status 
of the previous command. The problem is, if I cat out the file, it 
returns 0, overwriting the return status read by the %(0?%) directive, 
and guaranteeing that I will always get a prompt indicating success. 
What can I do about this?

Here's the whole line. The breakdown is: current temperature, pwd, (if 
last command successful, a green smiley, else a red frowny), prompt 
char.

export PS1='`cat /tmp/temperature`'" %m%~ %(0?."`echo 
'%{\e[1;32m%}:)%{\e[0m%}'`"."`echo \
'%{\e[1;31m%}:(%{\e[0m%}'`") %# "

(/tmp/temperature is refreshed every five minutes by a cron job, in 
case you were wondering.)
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Re: Execute a Command in PS1 w/o Disturbing Previous Return Value?

[Philippe Troin]

Aaron Davies <agdavi01@louisville.edu> writes:

> I'm trying to write a prompt that will do two things: include a file
> frequently re-downloaded from the web, and indicate the return status
> of the previous command. The problem is, if I cat out the file, it
> returns 0, overwriting the return status read by the %(0?%) directive,
> and guaranteeing that I will always get a prompt indicating
> success. What can I do about this?
> 
> Here's the whole line. The breakdown is: current temperature, pwd, (if
> last command successful, a green smiley, else a red frowny), prompt
> char.
> 
> export PS1='`cat /tmp/temperature`'" %m%~ %(0?."`echo
> '%{\e[1;32m%}:)%{\e[0m%}'`"."`echo \
> '%{\e[1;31m%}:(%{\e[0m%}'`") %# "
> 
> (/tmp/temperature is refreshed every five minutes by a cron job, in
> case you were wondering.)

What about:

 precmd() { 
   local r=$?
   psvar=()
   psvar=("$(< /tmp/temperature)") 
   (( $r )) && psvar=($psvar $r)
 }

 export PS1="$(print '%1v %m%~ %(2v,%{\e[1;31m%}:( [%2v]%{\e[0m%},%{\e[1;32m%}:%)%{\e[0m%}) %# ')"

I prefer "setopt printexitvalue" myself...

Phil.

Re: Execute a Command in PS1 w/o Disturbing Previous Return Value?

[Bart Schaefer]

On Thu, 12 Aug 2004, Aaron Davies wrote:

> I'm trying to write a prompt that will do two things: include a file 
> frequently re-downloaded from the web, and indicate the return status of 
> the previous command. The problem is, if I cat out the file, it returns 
> 0, overwriting the return status read by the %(0?%) directive

This should probably be considered a bug.

> What can I do about this?

In addition to Philippe's suggestion of using precmd so that $? is saved
and restored for you by the shell -- which is what should be happening 
during command substitutions in prompt expansion, but isn't -- a simple
alternative is to use $(<...) instead of `cat ...`.

You can also use $'...' instead of `echo '...'`

export PS1='$(</tmp/temperature)'" %m%~ %(0?."\
$'%{\e[1;32m%}:)%{\e[0m%}.%{\e[1;31m%}:(%{\e[0m%}'") %# "

Re: Execute a Command in PS1 w/o Disturbing Previous Return Value?

[Aaron Davies]

On Friday, August 13, 2004, at 01:32 PM, Bart Schaefer wrote:

> On Thu, 12 Aug 2004, Aaron Davies wrote:
>
>> I'm trying to write a prompt that will do two things: include a file
>> frequently re-downloaded from the web, and indicate the return status 
>> of
>> the previous command. The problem is, if I cat out the file, it 
>> returns
>> 0, overwriting the return status read by the %(0?%) directive
>
> This should probably be considered a bug.

I dunno, I can see where someone might want a prompt so complicated it 
needed internal error-handling based on return value of executed 
commands (cat foo || cat bar, etc.). Would "fixing" this prevent that?

>> What can I do about this?
>
> In addition to Philippe's suggestion of using precmd so that $? is 
> saved
> and restored for you by the shell -- which is what should be happening
> during command substitutions in prompt expansion, but isn't -- a simple
> alternative is to use $(<...) instead of `cat ...`.
>
> You can also use $'...' instead of `echo '...'`
>
> export PS1='$(</tmp/temperature)'" %m%~ %(0?."\
> $'%{\e[1;32m%}:)%{\e[0m%}.%{\e[1;31m%}:(%{\e[0m%}'") %# "

Thank you, that works perfectly!
-- 
     __                      __
    /  )                    /  )
   /--/ __. .__  ______    /  / __. , __o  _  _
  /  (_(_/|_/ (_(_) / (_  (__/_(_/|_\/ <__</_/_)_

Re: Execute a Command in PS1 w/o Disturbing Previous Return Value?

[Phil!Gregory]

* Aaron Davies <agdavi01@louisville.edu> [2004-08-14 12:07 -0400]:
> I dunno, I can see where someone might want a prompt so complicated it 
> needed internal error-handling based on return value of executed 
> commands (cat foo || cat bar, etc.). Would "fixing" this prevent that?

Shouldn't.  IIRC, the code for precmd is as simple as saving $? at the
beginning and then restoring it at the end.

(I ran into this problem a while ago and solved it by simply moving all
execution into precmd().)

-- 
...computer contrarian of the first order... / http://aperiodic.net/phil/
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