R help - Apr 2010 - Linux System Function

How do I pass a filename as an argument to the system command to count the
number of records in that file? I only know how to do it by hardcoding it.

HARDCODING EXAMPLE
> test <- matrix(1:20,ncol=5)
> write(x = test,file = "test.txt")
> records <- as.numeric(system("cat test.txt | wc -l",intern =
TRUE))
> records
[1] 4

??? NON-HARCODING EXAMPLE ???
> file = "test.txt"
> records <- as.numeric(system("cat file | wc -l",intern =
TRUE))
cat: file: No such file or directory
> records <- as.numeric(system("cat" test.txt "| wc
-l",intern = TRUE))
Error: unexpected symbol in "records <-
as.numeric(system("cat" test.txt"

TFYH

-- 
View this message in context:
http://r.789695.n4.nabble.com/Linux-System-Function-tp2063058p2063058.html
Sent from the R help mailing list archive at Nabble.com.

On Apr 23, 2010, at 6:07 PM, Ryan Garner wrote:
> 
> How do I pass a filename as an argument to the system command to count the
> number of records in that file? I only know how to do it by hardcoding it.
> 
> HARDCODING EXAMPLE
>> test <- matrix(1:20,ncol=5)
>> write(x = test,file = "test.txt")
>> records <- as.numeric(system("cat test.txt | wc -l",intern
= TRUE))
>> records
> [1] 4
> 
> ??? NON-HARCODING EXAMPLE ???
>> file = "test.txt"
>> records <- as.numeric(system("cat file | wc -l",intern =
TRUE))
> cat: file: No such file or directory
>> records <- as.numeric(system("cat" test.txt "| wc
-l",intern = TRUE))
> Error: unexpected symbol in "records <-
as.numeric(system("cat" test.txt"
> 
> TFYH

See ?paste

file <- "test.txt"
cmd <- paste("cat", file, "| wc -l")
> cmd
[1] "cat test.txt | wc -l"

Then use:

as.numeric(system(cmd, intern = TRUE))

HTH,

Marc Schwartz