TeeRb - Several ways to capture and tee Ruby's standard input and output

Pipe calls to $stdout and $stderr to a file
Pipe calls to $stdout and $stderr to an instance of Ruby's logger class
Pipe calls to an instance of Ruby's logger class to $stdout

Motivation and considerations

I wrote this gem for three reasons:

Have Ruby's logger library output to STDOUT/STDERR in addition to a file
Have the puts statements of external libraries go through my custom logger class
Tee STDOUT/STDERR to a file

In general, I consider redirecting Ruby's STDOUT and STDERR from within the program to be a last resort, because another person using your program might not expect this special behavior.

Most of the time it is possible to use standard Unix tools to accomplish the same task without having to change your program. Here are a few examples:

$: ruby myscript.rb > my_file.log
$: ruby myscript.rb | tee myfile.log

In particular, I consider it good practise to use the operating system's logging facilities (see man logger). This allows to change the logging behaviour without changing the actual program:

$: ruby myscript.rb | logger

If you want to have logs on the console as well:

$: ruby myscript.rb | tee /dev/null | logger

Problems

This only works for $stdout and $stderr and not for STDOUT and STDERR, since they are constants that should not be reassigned/redefined.

Installation

$: gem install teerb

Usage

# Tee $stdout and $stderr to several files
log_file = File.open("debug.log", "a")
tee = TeeRb::Tee.new(log_file)
tee.enable

puts 'puts hello'
$stdout.puts 'stdout hello'
$stderr.puts 'stderr hello'

tee.disable

puts 'puts hello'
$stdout.puts 'stdout hello'
$stderr.puts 'stderr hello'

# same as above but with block syntax
log_file = File.open("debug.log", "a")
TeeRb::Tee.new(log_file) do
  puts 'puts hello'
  $stdout.puts 'stdout hello'
  $stderr.puts 'stderr hello'
end


# Capture $stdout and $stderr and send it through `logger`
require 'logger'
log_file = File.open("debug.log", "a")
logger = Logger.new(log_file)
tee = TeeRb::LoggerTee.new(logger)
tee.enable

logger.warn "hello"
$stderr.puts "stderr hello"
puts "stdout hello"


# Pipe calls to an instance of Ruby's logger class to $stdout
require 'logger'
log_file = File.open("debug.log", "a")
logger = Logger.new(TeeRb::IODelegate.new(log_file, STDOUT))
logger.warn "warn"
$stderr.puts "stderr hello"
puts "stdout hello"

teerb

Development

TeeRb - Several ways to capture and tee Ruby's standard input and output

Motivation and considerations

Problems

Installation

Usage