# Piping two shell commands together **URL:** \ **Category:** Ruby\ **Created:** [August 2, 2007, 6:41pm UTC](https://www.ruby-forum.com/t/piping-two-shell-commands-together/111106 "2007-08-02T18:41:38Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![Hans\_F](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/a587f6/32.png) [@Hans\_F](https://www.ruby-forum.com/u/Hans_F)\ **Post date:** [August 2, 2007, 6:41pm UTC](https://www.ruby-forum.com/t/piping-two-shell-commands-together/111106/1 "2007-08-02T18:41:38Z")
I want to pipe two system commands together from within ruby. cmd1 and cmd2 are arrays, e.g. cmd1 = [‘oggdec’,’-o’,’-’,oldpath] cmd2 = [‘lame’,’-’,newpath] I think I can do the following, IO.popen(’-’,‘r’) do |p1| exec cmd1 unless p1 IO.popen(’-’,‘w’) do |p2| exec cmd2 unless p2 p2.write(p1.read) end end but I don’t like the line “p2.write(p1.read)”, because I think it will read into memory from p1 before turning around and writing it to p2. This may work for the above example, but it’s not very pipelike and I worry that read might return early (I’m not sure what the semantics of that are in Ruby, but in C I’d have to account for that). Plus I don’t like the popen ‘-’/exec combination. I’d love a more elgant, efficient, and/or safer idiom if anyone can think of one. ---
**Author:** ![Hans\_F](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/a587f6/32.png) [@Hans\_F](https://www.ruby-forum.com/u/Hans_F)\ **Post date:** [August 2, 2007, 6:49pm UTC](https://www.ruby-forum.com/t/piping-two-shell-commands-together/111106/2 "2007-08-02T18:49:39Z")
`#{cmd1.join(' ')} | #{cmd2.join(' ')}` Those are backticks. Let the system handle piping with the ‘|’ character. Jason ---
**Author:** ![Hans\_F](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/a587f6/32.png) [@Hans\_F](https://www.ruby-forum.com/u/Hans_F)\ **Post date:** [August 2, 2007, 7:36pm UTC](https://www.ruby-forum.com/t/piping-two-shell-commands-together/111106/3 "2007-08-02T19:36:54Z")
Hans F. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > I want to pipe two system commands together from within ruby. cmd1 and > cmd2 are arrays, e.g. > > cmd1 = [‘oggdec’,‘-o’,‘-’,oldpath] > cmd2 = [‘lame’,‘-’,newpath] I don’t know about the arrays, but you can say IO.popen (“oggdec | lame”)… m. ---
**Author:** ![Hans\_F](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/a587f6/32.png) [@Hans\_F](https://www.ruby-forum.com/u/Hans_F)\ **Post date:** [August 2, 2007, 7:40pm UTC](https://www.ruby-forum.com/t/piping-two-shell-commands-together/111106/4 "2007-08-02T19:40:54Z")
matt neuburg wrote: > Yeah, that won’t work here (unless there’s a reliable way to shell-quote/escape oldpath and newpath). ---
**Author:** ![Hans\_F](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/a587f6/32.png) [@Hans\_F](https://www.ruby-forum.com/u/Hans_F)\ **Post date:** [August 2, 2007, 8:52pm UTC](https://www.ruby-forum.com/t/piping-two-shell-commands-together/111106/5 "2007-08-02T20:52:08Z")
Hans F. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > > lame")… m. > > Yeah, that won’t work here (unless there’s a reliable way to > shell-quote/escape oldpath and newpath). I’m a little confused about oldPath. Once you have told IO.popen to generate an IO instance (let’s call it ios), whatever you write to ios passes thru the process. So you don’t actually need to tell IO.popen about oldpath; you just write the data. As for quoting, I just put quotes around it. So, for example, a way to do LAME encoding with Ruby is like this: oldpath = “/Users/mattneub/some sound file.aif” newpath = “/Users/mattneub/some sound file.mp3” s = “lame --preset standard - ‘#{newpath}’” IO.popen(s, “r+”) do |ios| ios.write(File.read(oldpath)) end So maybe you could say: s = “oggdec -R -o - - | lame … - ‘#{newpath}’” I’ve suggested -R because the oggdec man page warns not to write WAV to stdout. But then I’ve omitted some lame params (…) because you’ll probably need to tell lame what kind of raw data it’s receiving. I haven’t tried this, though. m. ---
**Author:** ![Hans\_F](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/a587f6/32.png) [@Hans\_F](https://www.ruby-forum.com/u/Hans_F)\ **Post date:** [August 2, 2007, 9:22pm UTC](https://www.ruby-forum.com/t/piping-two-shell-commands-together/111106/6 "2007-08-02T21:22:12Z")
On Aug 2, 2007, at 10:40 AM, Hans F. wrote: > end > end an alternative: cfp:~ \> ruby a.rb 1073741824 1073741824 cfp:~ \> cat a.rb require ‘open4’ cmd1 = ‘ruby -e" (2 \*\* 10).times{ STDOUT.write 0.chr \* 2\*\*20 } "’ cmd2 = ‘ruby -e" puts ARGF.read.size "’ stdin = IO.popen cmd1 stdout, stderr = ‘’, ‘’ status = Open4.spawn cmd2, 0=\>stdin, 1=\>stdout, 2=\>stderr puts stdout puts 2 \*\* 30 a @ [http://drawohara.com/](http://drawohara.com/) ---
**Author:** ![Hans\_F](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/a587f6/32.png) [@Hans\_F](https://www.ruby-forum.com/u/Hans_F)\ **Post date:** [August 3, 2007, 3:30am UTC](https://www.ruby-forum.com/t/piping-two-shell-commands-together/111106/7 "2007-08-03T03:30:42Z")
matt neuburg [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > s = “oggdec -R -o - - | lame … - ‘#{newpath}’” > > I’ve suggested -R because the oggdec man page warns not to write WAV to > stdout. But then I’ve omitted some lame params (…) because you’ll > probably need to tell lame what kind of raw data it’s receiving. I > haven’t tried this, though. Yes, I just tried it. (Had to download and compile and install the ogg stuff first.) I started with a mono aiff file; then I ogg’ed using the default setting. Then I said: oldpath = “/Users/mattneub/some sound file.ogg” newpath = “/Users/mattneub/some sound file.mp3” s = “oggdec -R -o - - | lame -r -x -m m --preset standard - ‘#{newpath}’” IO.popen(s, “r+”) do |ios| ios.write(File.read(oldpath)) end Worked great. If your file isn’t mono, leave out the “-m m”. If your native endianity does not require it, leave out the “-x”. Looks pretty “pipey” to me! m. ---
**Author:** ![Hans\_F](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/a587f6/32.png) [@Hans\_F](https://www.ruby-forum.com/u/Hans_F)\ **Post date:** [August 5, 2007, 8:11pm UTC](https://www.ruby-forum.com/t/piping-two-shell-commands-together/111106/8 "2007-08-05T20:11:27Z")
matt neuburg wrote: > > > I don’t know about the arrays, but you can say IO.popen ("oggdec | > > > As for quoting, I just put quotes around it. > > > So maybe you could say: > > s = “oggdec -R -o - - | lame … - ‘#{newpath}’” > > I’ve suggested -R because the oggdec man page warns not to write WAV to > stdout. But then I’ve omitted some lame params (…) because you’ll > probably need to tell lame what kind of raw data it’s receiving. I > haven’t tried this, though. What happens when you try to encode to newpath = “Beethoven’s 5th” or something with an apostrophe? I did come up with a working solution, which you can read about here: [http://hans.fugal.net/blog/articles/2007/08/02/pipelining-processes-in-ruby](http://hans.fugal.net/blog/articles/2007/08/02/pipelining-processes-in-ruby) Cheers ---
**Author:** ![Hans\_F](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/a587f6/32.png) [@Hans\_F](https://www.ruby-forum.com/u/Hans_F)\ **Post date:** [August 3, 2007, 4:29am UTC](https://www.ruby-forum.com/t/piping-two-shell-commands-together/111106/9 "2007-08-03T04:29:51Z")
Hi, At Fri, 3 Aug 2007 01:40:00 +0900, Hans F. wrote in [ruby-talk:263040]: > I want to pipe two system commands together from within ruby. cmd1 and > cmd2 are arrays, e.g. > > cmd1 = [‘oggdec’,’-o’,’-’,oldpath] > cmd2 = [‘lame’,’-’,newpath] IO.popen(’-’,‘r’) do |p1| exec(\*cmd1) unless p1 IO.popen(’-’,‘w’) do |p2| unless p2 STDIN.reopen(p1) exec(\*cmd2) end end end