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comp.lang.ruby

backticks asynchronous?

Giles Bowkett

11/19/2006 11:06:00 PM

sorry, dumb question possibly, I just want to make sure. if I call
some Unix command using backticks, that invokes the command, launches
a new process, and waits until that process terminates before resuming
program execution, right? especially if I do this:

shell_output = `some process`

which should capture the output of the process. right? it isn't possible to say

shell_output = `some process`

and accidentally see execution fork, is it?

--
Giles Bowkett
http://www.gilesg...
5 Answers

Logan Capaldo

11/19/2006 11:13:00 PM

0

On Mon, Nov 20, 2006 at 08:05:45AM +0900, Giles Bowkett wrote:
> sorry, dumb question possibly, I just want to make sure. if I call
> some Unix command using backticks, that invokes the command, launches
> a new process, and waits until that process terminates before resuming
> program execution, right? especially if I do this:
>
> shell_output = `some process`
>
> which should capture the output of the process. right? it isn't possible to
> say
>
> shell_output = `some process`
>
> and accidentally see execution fork, is it?
>
Right, ruby will wait for the process to complete.
> --
> Giles Bowkett
> http://www.gilesg...

Paul Lutus

11/20/2006 2:32:00 AM

0

Giles Bowkett wrote:

> sorry, dumb question possibly, I just want to make sure. if I call
> some Unix command using backticks, that invokes the command, launches
> a new process, and waits until that process terminates before resuming
> program execution, right? especially if I do this:
>
> shell_output = `some process`
>
> which should capture the output of the process. right? it isn't possible
> to say
>
> shell_output = `some process`
>
> and accidentally see execution fork, is it?

That depends on what you put between the back-ticks.

This:

`command > /dev/null &`

will almost certainly fork. There are any number of forking contingencies,
depending on what you try to run, and how.

--
Paul Lutus
http://www.ara...

Joel VanderWerf

11/20/2006 3:39:00 AM

0

Jason Mayer wrote:
> Sorry, reading this email reminded me of my project. Say I wanted to do a
> bunch of pings using backticks (you may have asked my stupid n00b questin
> about ``). If I wanted to do a bunch of pings, which would take some small
> amount of time, would it be better(faster) to start new threads before
> doing
> the `ping whatever`, or is there a better/different way?

Sure, why not use threads:

t0 = Time.now

threads = (1..10).map do |i|
Thread.new do
addr = "192.168.0.#{i}"
[addr, `ping -w3 -nq #{addr}`]
end
end

values = threads.map {|thread| thread.value}
t1 = Time.now
puts "Finished in #{t1 - t0} seconds"

require 'yaml'
y values.select {|addr, out| out !~ / 0 received/}

__END__

Output:

Finished in 3.011614 seconds
---
- - 192.168.0.1
- |
PING 192.168.0.1 (192.168.0.1) 56(84) bytes of data.

--- 192.168.0.1 ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2001ms
rtt min/avg/max/mdev = 2.032/3.052/4.750/1.210 ms

...

--
vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407

Giles Bowkett

11/20/2006 4:46:00 AM

0

> That depends on what you put between the back-ticks.
>
> This:
>
> `command > /dev/null &`
>
> will almost certainly fork. There are any number of forking contingencies,
> depending on what you try to run, and how.

well, that's probably it. the command I'm using is a very long,
involved command to a complex utility that handles media files, and
apparently takes an infinite number of command-line arguments, but the
final args are "2>&1". I inherited this code, as I understand it that
just pipes standard error and standard out to the same place --
however, now I think that might be what's going wrong.

--
Giles Bowkett
http://www.gilesg...

Giles Bowkett

11/20/2006 4:59:00 AM

0

ok never mind about that last post. it does appear to be pipe commands
for standard out and standard err and that shouldn't result in
backgrounding.

On 11/19/06, Giles Bowkett <gilesb@gmail.com> wrote:
> > That depends on what you put between the back-ticks.
> >
> > This:
> >
> > `command > /dev/null &`
> >
> > will almost certainly fork. There are any number of forking contingencies,
> > depending on what you try to run, and how.
>
> well, that's probably it. the command I'm using is a very long,
> involved command to a complex utility that handles media files, and
> apparently takes an infinite number of command-line arguments, but the
> final args are "2>&1". I inherited this code, as I understand it that
> just pipes standard error and standard out to the same place --
> however, now I think that might be what's going wrong.
>
> --
> Giles Bowkett
> http://www.gilesg...
>


--
Giles Bowkett
http://www.gilesg...