Re: ruby tail


#1

Actually, I am not sure how this would work. If I do this, I get no
output from the file:

tail -f sim.out

So there is something basic I am missing here. Any help?

TIA,
Phy

----- Original Message ----
From: Kevin J. removed_email_address@domain.invalid
To: ruby-talk ML removed_email_address@domain.invalid
Sent: Thursday, February 22, 2007 1:33:19 AM
Subject: Re: ruby tail

Is there a gem or perhaps a method I am not aware of that does the similar function of tail? Or is there a way to use tail in ruby? I have a file that I want to process as new data is appended to the file. This is easy enough using tail and tail has the added advantage that it can follow a file if it is “rolled”.

Just call out to tail

def tail(f)
tail f
end

or similar - if tail does what you want, use it

Kev


#2

Actually, I am not sure how this would work. If I do this, I get no output from the file:

tail -f sim.out

So there is something basic I am missing here. Any help?

it shells out to the process and waits for it to return - with -f does
tail ever return? if not you may not be able to use it - AFAIK ` and
exec are the same - someone with better ruby knowledge may be able to
offer a solution - perhaps using threads or something

Kev


#3

Kevin J. wrote:

offer a solution - perhaps using threads or something
Use IO.popen:

IO.popen(‘tail -f sim.out’){|f|
while line = f.gets
p line
end
}


#4

removed_email_address@domain.invalid wrote:

offer a solution - perhaps using threads or something

I haven’t ever done that, but it looks like it from the docs…


#5

exec are the same - someone with better ruby knowledge may be able to
offer a solution - perhaps using threads or something
Use IO.popen:

IO.popen(‘tail -f sim.out’){|f|
while line = f.gets
p line
end
}

Out of interest, the blocking call is “gets” here, right? Can you use
Kernel.select on a bunch of those handles?

Cheers,
Benj


#6

On 22.02.2007 10:59, Alex Y. wrote:

exec are the same - someone with better ruby knowledge may be able to
offer a solution - perhaps using threads or something
Use IO.popen:

IO.popen(‘tail -f sim.out’){|f|
while line = f.gets
p line
end
}

You can do it in pure Ruby:

11:14:14 [Temp]: rm x; for ((i=0;i<30;++i)); do echo $i; sleep 0.2; done

x & ruby tail.rb
removed x' [1] 2252 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 [1]+ Done for ((i=0; i<30; ++i)) do echo $i; sleep 0.2; done > x tail.rb:12:insleep’: Interrupt
from tail.rb:12:in tail' from tail.rb:5:inloop’
from tail.rb:5:in `tail’
from tail.rb:16
11:14:31 [Temp]: cat tail.rb

we never return!

def tail(file)
io = File.open(file)

loop do
while ( line = io.gets )
puts line
end

 # uncomment next to watch what is happening
 # puts "-"
 sleep 1

end
end

tail “x”
11:14:35 [Temp]:

Kind regards

robert


#7

This version is safer and a tad more flexible, just in case there is an
exception (e.g. because of thread interruption):

def tail(file, interval=1)
raise “Illegal interval #{interval}” if interval < 0

File.open(file) do |io|
loop do
while ( line = io.gets )
puts line
end

   # uncomment next to watch what is happening
   # puts "-"
   sleep interval
 end

end
end

Cheers

robert