[R & Unix ..] system("test",...) gives funny results...

[Prof Brian Ripley]

> Date: Thu, 10 Dec 1998 14:57:58 +0100
> From: Martin Maechler <maechler@stat.math.ethz.ch>

> [in an attempt to provide 
> 
> 	  system.test <- 
> 		function(...) { system(paste("test", ...)) == 0 }
> and then 
> 	  file.exists <- 
> 		function(file){sapply(file, function(f)system.test("-e", f))} 
>  
>   (which would provide S-plus [>= 4.x] compatibility)
> ]
> 

But surely that is not the way to do this (and how is it going to work on
Windows?)  S-PLUS uses a system call for file.exists, presumably to
access(), even on Unix.

If you want to use test, do remember that what you get is shell-specific.
If you use

system("/usr/bin/test -e /tmp")

you have some chance of working on different shells. (Even Linux, RH5.2,
has test at /usr/bin/test!)


[still interested to hear about the potential of an R builtin 'test',
 relying on GNU sh-utils].

Why not use POSIX system calls instead?
-- 
Brian D. Ripley,                  ripley@stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272860 (secr)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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