Last active
March 2, 2023 08:48
-
-
Save chrisn/7450808 to your computer and use it in GitHub Desktop.
Ruby example of using Open3.popen3 with a select loop to read a child process's standard output and standard error streams.
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
#!/usr/bin/env ruby | |
require 'open3' | |
# Returns true if all files are EOF | |
# | |
def all_eof(files) | |
files.find { |f| !f.eof }.nil? | |
end | |
command = "ls -l" | |
puts "Running command: #{command}" | |
BLOCK_SIZE = 1024 | |
Open3.popen3(command) do |stdin, stdout, stderr| | |
stdin.close_write | |
begin | |
files = [stdout, stderr] | |
until all_eof(files) do | |
ready = IO.select(files) | |
if ready | |
readable = ready[0] | |
# writable = ready[1] | |
# exceptions = ready[2] | |
readable.each do |f| | |
fileno = f.fileno | |
begin | |
data = f.read_nonblock(BLOCK_SIZE) | |
# Do something with the data... | |
puts "fileno: #{fileno}, data: #{data}" | |
rescue EOFError => e | |
puts "fileno: #{fileno} EOF" | |
end | |
end | |
end | |
end | |
rescue IOError => e | |
puts "IOError: #{e}" | |
end | |
end | |
puts "Done" |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Hi, thanks for sharing this code 😄
Beware that
IO#eof
blocks the current thread until the IO is ready to read(which you may wanted to handle byIO.select
).As result:
all_eof(files)
blocks whenstderr
is flowing butstdout
is stopped.stderr
is never read untilstdout
is ready.ready = IO.select(files)
always return immediately(because at line 23 of your code, you already waited for all thefiles
to be read-ready)I guess what you may want to do is:
Btw, I've managed to write a
wrapper
command(wrapper cat
acts the same ascat
) thanks to your code :)https://github.com/crowdworks/joumae-ruby/blob/master/lib/joumae/command.rb#L32