How do I redirect stderr and stdout to file for a Ruby script?

Question

How do I redirect stderr and stdout to file for a Ruby script?

Answer 1

From within a Ruby script, you can redirect stdout and stderr with the IO#reopen method.

# a.rb
$stdout.reopen("out.txt", "w")
$stderr.reopen("err.txt", "w")

puts 'normal output'
warn 'something to stderr'

$ ls
a.rb
$ ruby a.rb
$ ls
a.rb    err.txt out.txt
$ cat err.txt 
something to stderr
$ cat out.txt 
normal output

Answer 2

Note: reopening of the standard streams to /dev/null is a good old method of helping a process to become a daemon. For example:

# daemon.rb
$stdout.reopen("/dev/null", "w")
$stderr.reopen("/dev/null", "w")

Answer 3

def silence_stdout
  $stdout = File.new( '/dev/null', 'w' )
  yield
ensure
  $stdout = STDOUT
end

Answer 4

./yourscript.rb 2>&1 > log.txt

will redirect stdout and stderr to the same file.