defining real time variables for a shell

defining real time variables for a shell

[Eric Smith]

Hi zshellers

What would be a good way to define in a shell a variable for say currencies
like I want to define $USD as 1.33 and $GBP as 1.44 for example.

These values need to be updated at least daily and must be
available to shells that are already open (I use screen and am
lazy). 

I am thinking maybe to use a preexec function that parses a file
with the values.

Thanks!

-- 
Eric Smith

Re: defining real time variables for a shell

[Bart Schaefer]

On Mar 20,  6:05pm, Eric Smith wrote:
> 
> These values need to be updated at least daily and must be
> available to shells that are already open (I use screen and am
> lazy). 
> 
> I am thinking maybe to use a preexec function that parses a file
> with the values.

You'd want precmd, rather than preexec, I think.  It depends on what
you want to do with the values.  Re-parsing a file before every prompt
or command may be overkill; at the least, look at the zsh/sched module
and consider updating the variables less frequently.

(People tend to ask "How do I train a cat to dance?" when what they
really want to know is "How do I entertain twelve eight-year-olds
for two hours?"  A dancing cat might keep kids happy, but it might
not be the right or best solution.)

You say perhaps parse a file.  Where do the values in the file come
from?  The values will go into shell variables.  Why?  Is it because
you want to export them in the environment so external commands can
reference them?  If not, maybe there's no need for variables at all.
Or maybe $USD could be an expression that computes the number value,
and when you need the number you use ${(e)USD}.

Just food for thought.

Re: defining real time variables for a shell

[Eric Smith - Fruitcom]

Thanks Bart.

According to Bart Schaefer on Sun, Mar 20, 2005 at 11:58:22AM -0800:
}   On Mar 20,  8:08pm, Eric Smith - Fruitcom wrote:
}   > Subject: Re: defining real time variables for a shell
}   > Thanks Bart 
}   
}   (Did you intentionally send this only to me, and not to the list?  No big
}   deal, I just wondered.)

Sorry, just carelessness.

}   > I would like to have the forex rates in vars in order to do
}   > my arithmatic on the command line.
}   
}   Ah, OK.  In that case I think a sched command is indeed the way to go.
}   
}   > This rule in my prexec() make it easy for me to do math fast:
}   > elif [[ $cmd[1] == [\(\)0-9]* ]]; then
}   >     application=calc
}   > ( I think you wrote that one for me :) )

Yeah, when I have a moment, I will write how I apply this command line
"mailcap" to most things I do.  For example entering a pdf file on one machine will
launch a pdf viewer while doing the same thing on my remote server will
submit that pdf to hylafax (which sends it to the fax numbers  in the 
header section of the pdf).

}   Sort of; in fact, I just made reference to that thread in a zsh-workers
}   posting a few minutes ago.
}   
}   > so I might do something like:
}   > 
}   > '(15/$GBP)+(3750/1900)'
}   > .... ooops - I see it is more complicated than i thought
}   > to have all your cake and eat it all :)
}   
}   Just get rid of the $ sign -- it's not necessary in math context unless
}   you're referring to something like the length of a string with $#scalar
}   or the number of arguments $# or a positional parameter like $3.
}   
}   	'(15/GBP)+(3750/1900)'

Huh?  the GBP is a var, how can a bare string be interpolated.
[eric@pepper ~] $ "(15/GBP)+(3750/1900)"
"GBP" is undefined

Re: defining real time variables for a shell

[Bart Schaefer]

On Mar 20,  9:09pm, Eric Smith - Fruitcom wrote:
}
} }   > elif [[ $cmd[1] == [\(\)0-9]* ]]; then
} }   >     application=calc
} }   > ( I think you wrote that one for me :) )
} 
} Yeah, when I have a moment, I will write how I apply this command line
} "mailcap" to most things I do.

I think you did already:  zsh-users/6463 ?

} }   > '(15/$GBP)+(3750/1900)'
} }   
} }   Just get rid of the $ sign -- it's not necessary in math context
} }   
} }   	'(15/GBP)+(3750/1900)'
} 
} Huh?  the GBP is a var, how can a bare string be interpolated.
} [eric@pepper ~] $ "(15/GBP)+(3750/1900)"
} "GBP" is undefined

Um, what's the application "calc"?

When you said "my arithmatic on the command line" I assumed you were
using zsh's built-in arithmetic, in which bare strings are treated as
variable references.

E.g.,

schaefer[509] calc() { print $(( $* )) }
schaefer[510] GBP=1.44
schaefer[511] calc '(15/GBP)+(3750/1900)'
11.416666666666668