hiding system command results in ruby

Question

How easy is it to hide results from system commands in ruby? For example, some of my scripts run

system "curl ..."

and I would not prefer to see the results of the download.

possible duplicate of [Suppressing the output of a command run using 'system' method while running it in a ruby script](http://stackoverflow.com/questions/1960838/suppressing-the-output-of-a-command-run-using-system-method-while-running-it-i) — Ciro Santilli OurBigBook.com, Oct 17 '14 at 19:59

score 16 · Answer 1 · answered May 15 '18 at 14:12

16

To keep it working with system without modifying your command:

system('curl ...', :err => File::NULL)

answered May 15 '18 at 14:12

noraj

2

+1 Definitely the most elegant and simplest solution, since it uses the `system` function still, and isn't OS-specific. – Noldorin Apr 20 '19 at 16:58
2

You can also use `[ :out, :err ] => File::NULL` if you want to redirect both `out` and `err`. – Joshua Pinter Dec 30 '20 at 04:45

score 11 · Answer 2 · answered Jun 06 '12 at 20:51

11

You can use the more sophisticated popen3 to have control over STDIN, STDOUT and STDERR separately if you like:

Open3.popen3("curl...") do |stdin, stdout, stderr, thread|
  # ...
end

If you want to silence certain streams you can ignore them, or if it's important to redirect or interpret that output, you still have that available.

answered Jun 06 '12 at 20:51

tadman

3

You may need to "require 'open3'". Use "myvarname = stdin.read" if you want to process output. – DanielaWaranie Nov 20 '14 at 03:11
To use advanced outputs like stdin, stderr etc. it's okay, but just to get the output of the console it's a dependency which can be eliminated with e.g. `%x{bash-command arg1 arg2}` – siegy22 May 12 '16 at 11:41
1

@RaVeN One advantage of `popen3` or `system` is you can properly break out arguments: `system("example", "--file", user_supplied_filename)` is safe from shell injection. `system("example --file #{user_supplied_filename}")` is **extremely dangerous** and should not be done. – tadman May 12 '16 at 16:23

score 5 · Answer 3 · answered Jun 06 '12 at 21:04

Easiest ways other than popen:

Use %x instead of system. It will automatically pipe

rval = %x{curl ...}       #rval will contain the output instead of function return value

Manually pipe to /dev/null. Working in UNIX like system, not Windows
```
system "curl ... > /dev/null"
```

fl00r · Answer 4 · 2012-06-06T21:10:18.457

2

The simplest one is to redirect stdout :)

system "curl ... 1>/dev/null"
# same as
`curl ... 1>/dev/null`

edited Jun 06 '12 at 21:10

answered Jun 06 '12 at 20:56

fl00r

4 Answers4