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I'm trying to obtain the current version of nginx in Ruby. I've tried all of these, and nothing seems to work:

a = `nginx -v`
puts a             # ==> nil
a = `nginx -V`
puts a             # ==> nil again
a = system('nginx -v')
puts a             # ==> nil

Anybody know how I can obtain this data? Strange behaviour. Same for postgres and ruby work fine.

razvans
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Rich_F
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1 Answers1

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There are a handful of methods that can run system commands and all of them are working differently. For example `date` works different than system('date'). More here.

Also, some commands write to STDOUT, some to STDERR and, apparently nginx -v writes to STDERR. For this scenario there's another option which gives access to more info: Open3

require 'open3'
stdout, stderr, status = Open3.capture3("nginx -v")
# ["", "nginx version: nginx/1.21.6\n", #<Process::Status: pid 22253 exit 0>] 

stdout, stderr, status = Open3.capture3("date")
# ["Sun Jan 30 12:55:29 EET 2022\n", "", #<Process::Status: pid 22264 exit 0>]

stdout, stderr, status = Open3.capture3("ruby -v")
["ruby 2.7.5p203 (2021-11-24 revision f69aeb8314) [arm64-darwin21]\n", "", #<Process::Status: pid 22571 exit 0>]
razvans
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  • OK, I have that in my arsenal. Even so, if the `CLI` (`zsh`) shows that output, would it not be returned to the `method` for the first two? – Rich_F Jan 30 '22 at 14:45
  • You are right, the output will not be returned to the variable even if you see it in the terminal. – razvans Jan 30 '22 at 20:40