# Stderr stdout redirection with Ruby? **URL:** \ **Category:** Ruby\ **Created:** [August 10, 2007, 11:32am UTC](https://www.ruby-forum.com/t/stderr-stdout-redirection-with-ruby/111742 "2007-08-10T11:32:02Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![unbewust](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/u/9d8465/32.png) [@unbewust](https://www.ruby-forum.com/u/unbewust)\ **Post date:** [August 10, 2007, 11:32am UTC](https://www.ruby-forum.com/t/stderr-stdout-redirection-with-ruby/111742/1 "2007-08-10T11:32:02Z")
i do have a shell script doing : `man "#{arg}" 2> "#{tmp}/#{fm}" PIPE man2html > "#{tmp}/#{f1}"` because i want to know if there is “No manual entry for “#{arg}”” then for the time being i’m using an tmp file “#{tmp}/#{fm}” which i read after to know i i get the message : “No manual entry for “#{arg}”” i’m sure there is a more elegant way doing that in Ruby, avoiding shelling, BUT HOW TO ? ---
**Author:** ![unbewust](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/u/9d8465/32.png) [@unbewust](https://www.ruby-forum.com/u/unbewust)\ **Post date:** [August 10, 2007, 1:27pm UTC](https://www.ruby-forum.com/t/stderr-stdout-redirection-with-ruby/111742/2 "2007-08-10T13:27:24Z")
> i’m sure there is a more elegant way doing that in Ruby, avoiding > shelling, BUT HOW TO ? If you want to do it completely within Ruby, you could first slurp the output of man into a Ruby variable, i.e. man\_page=%x(man #{arg}) and if it is OK, i.e. if man\_page.length \> 0 … send this as stdin into man2html, i.e. something like: to\_html=IO.popen(“man2html \>#{f1}”,“w”) to\_html.print(man\_page) to\_html.close From a logical point of view, this solution has the advantage that you don’t overwrite your file f1 if the man page does not exist. For a simpler solution (a bit dirty, but less keystrokes), you might consider the following idea, which however _does_ use a shell: error\_message=%x[(man #{arg}|man2html \>#{f1}) 2\>&1] After this, error\_message contains whatever man and/org man2html spilled out onto stderr, but f1 is always overwritten (even if there is no man page). HTH, Ronald ---
**Author:** ![unbewust](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/u/9d8465/32.png) [@unbewust](https://www.ruby-forum.com/u/unbewust)\ **Post date:** [August 10, 2007, 9:41pm UTC](https://www.ruby-forum.com/t/stderr-stdout-redirection-with-ruby/111742/3 "2007-08-10T21:41:27Z")
On Friday 10 August 2007 04:26:00 am Ronald F. wrote: > > > > if man\_page.length \> 0 > For a simpler solution (a bit dirty, but less keystrokes), you might > > Ronald By using ‘man\_page=%x(man #{arg})’ you’re shelling out as well. It’s the same as writing 'man\_page = `man #{arg}`'. However, it’s probably good to do the checking / conversion stuff inside ruby and shell out multiple times rather than having actual program flow / code in sh scripting :D. ---
**Author:** ![unbewust](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/u/9d8465/32.png) [@unbewust](https://www.ruby-forum.com/u/unbewust)\ **Post date:** [August 10, 2007, 3:06pm UTC](https://www.ruby-forum.com/t/stderr-stdout-redirection-with-ruby/111742/4 "2007-08-10T15:06:41Z")
On 10 août, 13:26, “Ronald F.” [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > if man\_page.length \> 0 > For a simpler solution (a bit dirty, but less keystrokes), you might > consider > the following idea, which however _does_ use a shell: > > error\_message=%x[(man #{arg}|man2html \>#{f1}) 2\>&1] > > After this, error\_message contains whatever man and/org man2html spilled > out onto stderr, but f1 is always overwritten (even if there is no man > page). OK, fine thanks, in fact f1 is never overwritten the way i use it … thanks a lot ! ---
**Author:** ![unbewust](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/u/9d8465/32.png) [@unbewust](https://www.ruby-forum.com/u/unbewust)\ **Post date:** [August 10, 2007, 11:03pm UTC](https://www.ruby-forum.com/t/stderr-stdout-redirection-with-ruby/111742/5 "2007-08-10T23:03:37Z")
On Aug 10, 2007, at 3:30 AM, unbewust wrote: > i’m sure there is a more elegant way doing that in Ruby, avoiding > shelling, BUT HOW TO ? > require ‘rubygems’ require ‘open4’ stdin = ‘’, stdout = ‘’, stderr = ‘’ Open4.spawn cmd, :stdin=\>stdin, :stdout=\>stdout, :stderr=\>stderr there are many example in the dist and postings on this list. a @ [http://drawohara.com/](http://drawohara.com/) ---
**Author:** ![unbewust](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/u/9d8465/32.png) [@unbewust](https://www.ruby-forum.com/u/unbewust)\ **Post date:** [August 11, 2007, 12:44pm UTC](https://www.ruby-forum.com/t/stderr-stdout-redirection-with-ruby/111742/6 "2007-08-11T12:44:28Z")
On 10 août, 23:02, “ara.t.howard” [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > stdin = ‘’, stdout = ‘’, stderr = ‘’ > > Open4.spawn cmd, :stdin=\>stdin, :stdout=\>stdout, :stderr=\>stderr > > there are many example in the dist and postings on this list. > > a @[http://drawohara.com/](http://drawohara.com/) Fine ! thanks a lot !!! ---
**Author:** ![unbewust](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/u/9d8465/32.png) [@unbewust](https://www.ruby-forum.com/u/unbewust)\ **Post date:** [August 11, 2007, 3:25pm UTC](https://www.ruby-forum.com/t/stderr-stdout-redirection-with-ruby/111742/7 "2007-08-11T15:25:42Z")
On 10 août, 23:02, “ara.t.howard” [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > stdin = ‘’, stdout = ‘’, stderr = ‘’ > > Open4.spawn cmd, :stdin=\>stdin, :stdout=\>stdout, :stderr=\>stderr i’ve tested allready, unfortunately i get a " undefined method spawn for main object" after having included it… Yvon ---
**Author:** ![unbewust](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/u/9d8465/32.png) [@unbewust](https://www.ruby-forum.com/u/unbewust)\ **Post date:** [August 11, 2007, 5:28pm UTC](https://www.ruby-forum.com/t/stderr-stdout-redirection-with-ruby/111742/8 "2007-08-11T17:28:03Z")
On 8/11/07, unbewust [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > > require ‘open4’ > > > > stdin = ‘’, stdout = ‘’, stderr = ‘’ > > > > Open4.spawn cmd, :stdin=\>stdin, :stdout=\>stdout, :stderr=\>stderr > > i’ve tested allready, unfortunately i get a " undefined method spawn > for main object" after having included it… Did you do this? include Open4 spawn cmd, … Because that’s not going to work spawn is a singleton method of the Open4 module. Yvon