Executing shell command in background from ruby with proper argument escaping

Question

I have to run a command in the background but I want to have proper escaping for its parameter.

system("rake send_mails subject='#{params[:subject]}' 2> /dev/null 1> /dev/null &");

If I write system("rake", "send_mails", params[:subject]) then I don't have "place" for redirections and the & sign. If I don't I do not have escaping for the subject parameter.

How can I resolve this?

I am not sure, but did you try to nest system calls? For example: system(system("rake", "send_mails", params[:subject]), "/dev/null 1> /dev/null &") — fl00r
– fl00r, Commented May 10, 2011 at 11:11
The inner system() call is executed then the outer system() fails without executing anything: TypeError: can't convert true into String — Notinlist
– Notinlist, Commented May 10, 2011 at 11:24

Lars Haugseth · Accepted Answer · 2011-05-10 12:05:29Z

20

In Ruby 1.9, try Process.spawn:

# Spawn a new process and run the rake command
pid = Process.spawn({"subject" => params[:subject]},
                    "rake", "send_mails",
                    :out => 'dev/null', :err => 'dev/null')

# Detach the spawned process
Process.detach pid

edited May 10, 2011 at 12:05

answered May 10, 2011 at 11:33

Lars Haugseth

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7 Comments

Notinlist Over a year ago

The point would be not to wait at all. We have to move on to processing the next web query - as I failed to mention it. But that's the point in redirecting the output to /dev/null and running with & - to reach complete detachment.

Lars Haugseth Over a year ago

Then use Process.detach after you've spawned the new process. I will edit my answer to include this.

Notinlist Over a year ago

Adding that Process.fork do ... end is available and close-to-perfect in 1.8.7.

Notinlist Over a year ago

But I am still hungry for a function like PHP's escapeshellarg().

radiospiel Over a year ago

I know it has been a while, but there is Shellwords: stackoverflow.com/questions/5949008/…

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