Re: Inconsistent type magic

[sfeam <sf...@us...>]

On Sunday, 02 March 2014 01:47:57 AM pl...@pi... wrote:
> Hi,
> 
> I'm trying to get a status result back from a system call but am getting 
> inconsistent behaviour from the automatic typecasting magic.
> 
> bash$ test=OK;echo $test; echo $?
> OK
> 0
> 
> gnuplot
>    Version 4.7 patchlevel 0    last modified 2012-10-16
> ....
> 
> gnuplot>   cmd="test=OK;echo $test; echo $?;"
> gnuplot>  res=0;print system (cmd);print res
> OK
> 0
> 0
> 
> gnuplot>  res=0;  res= system (cmd);print res
> OK
> 0
> 
> gnuplot> res=0; if (res==0) {print "test OK"}
> test OK
> 
> gnuplot>  res=0;  res=res+ system (cmd);print res
>           Non-numeric string found where a numeric expression was expected
> 
> gnuplot>  res=0;  res=res || system (cmd);print res
>           non-integer passed to boolean operator
> 
> 
> Now I know automatic typing is _supposed_ to be inconsistent ( it's a 
> feature not a bug). but this seems nonsensical.
> 
> The first and second invocations are as expected and prints integer zero 
> (the status result returned by the shell). So what the heck is it 
> complaining about when I try to add integer zero to integer zero?

gnuplot> help system
  `system "command"` executes "command" using the standard shell. See `shell`.
 If called as a function, `system("command")` returns the resulting character
 stream from stdout as a string.

Your printout above shows exactly this. 
After setting res = system(...) it is a string
containing "OK\n0"

> How is it that it manages to print the zero result directly but when I 
> try to add it , it suddenly becomes a "non numeric" expression? Then a 
> "non integer".

It doesn't print 0.  It prints "OK\n0"

> Is this really what it's supposed to be doing?

Yes.

	Ethan