Hi, Prof. Ripley,
Thanks for the reply. Mostly I want to capture output as it is written
to the stream. For example, I quite often do the following to view the
progress of a log file from a computationally intensive script.
1. Open a console and type:
Rscript script.R >& script.log
which directs both stdout and stderr to "script.log"
2. Open another console and type:
tail -f script.log
This way I get both the script's log file and its current progress.
I guess my question is: Is there a way to accomplish the "tail -f"
command in R?
Thanks,
--sundar
Prof Brian Ripley said the following on 11/20/2008 11:43 PM:
I am not sure what the issue is here. Do you want to capture both stderr
and stdout (use 2>1 in the command with an sh-like shell), or is the
problem that you don't get immediate output?
The latter is a Perl issue: you need to circumvent output buffering.
See e.g
http://perl.plover.com/FAQs/Buffering.html
Sundar Dorai-Raj wrote:
Hi,
I have an application in perl that prints some output to either stderr
or stdout.
Here's an example:
# tmp.pl
print STDERR "starting iterator\n";
for(my $i = 0; $i < 1000000; $i++) {
print $i . "\n";
}
# tmp.R
con <- pipe("perl tmp.pl")
r <- readLines(con, n = -1)
close(con)
However, the second line stalls until the perl for-loop finishes. What
I would like is to process each line as it comes. E.g. something like:
while(TRUE) {
r <- readLines(con, n = 1) # read one line
if(r == "10000") print(r)
if(length(r) == 0) break
}
Of course, this won't work since I'm not calling readLines
appropriately. Answers must work on Windows but may include cygwin
utilities if necessary. Any advice would be appreciated. Version info
at the end if it matters.
Thanks, --sundar
> version
_
platform i386-pc-mingw32
arch i386
os mingw32
system i386, mingw32
status
major 2
minor 8.0
year 2008
month 10
day 20
svn rev 46754
language R
version.string R version 2.8.0 (2008-10-20)
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