Rescue ruby command in shell script

Question

I have a simple sh script (file.command) which connects to an Amazon EC2 instance and afterwards performs a command twurl.... (in ruby).

#!/bin/sh

#Connect to Amazon EC2
ssh -i ~/.ssh/research.pem [email protected] twurl -t -d track=keyword  -H stream.twitter.com /1.1/statuses/filter.json

This command sometimes throws a timeout error. How can I rescue this error so that the command doesn't cancel?

Error:

/usr/lib/ruby/1.8/timeout.rb:64:in `rbuf_fill': execution expired (Timeout::Error)
from /usr/lib/ruby/1.8/net/protocol.rb:134:in `rbuf_fill'
from /usr/lib/ruby/1.8/net/protocol.rb:104:in `read_all'
from /usr/lib/ruby/1.8/net/http.rb:2228:in `read_body_0'
from /usr/lib/ruby/1.8/net/http.rb:2181:in `read_body'
from /usr/lib/ruby/gems/1.8/gems/twurl-0.8.3/bin/../lib/twurl/request_controller.rb:14:in `perform_request'
from /usr/lib/ruby/1.8/net/http.rb:1054:in `request'
from /usr/lib/ruby/1.8/net/http.rb:2144:in `reading_body'
from /usr/lib/ruby/1.8/net/http.rb:1053:in `request'
from /usr/lib/ruby/1.8/net/http.rb:1037:in `request'
from /usr/lib/ruby/1.8/net/http.rb:543:in `start'
from /usr/lib/ruby/1.8/net/http.rb:1035:in `request'
from /usr/lib/ruby/gems/1.8/gems/twurl-0.8.3/bin/../lib/twurl/oauth_client.rb:80:in `perform_request_from_options'
from /usr/lib/ruby/gems/1.8/gems/twurl-0.8.3/bin/../lib/twurl/request_controller.rb:13:in `perform_request'
from /usr/lib/ruby/gems/1.8/gems/twurl-0.8.3/bin/../lib/twurl/request_controller.rb:9:in `dispatch'
from /usr/lib/ruby/gems/1.8/gems/twurl-0.8.3/bin/../lib/twurl/abstract_command_controller.rb:7:in `dispatch'
from /usr/lib/ruby/gems/1.8/gems/twurl-0.8.3/bin/../lib/twurl/cli.rb:38:in `dispatch'
from /usr/lib/ruby/gems/1.8/gems/twurl-0.8.3/bin/../lib/twurl/cli.rb:21:in `run'
from /usr/lib/ruby/gems/1.8/gems/twurl-0.8.3/bin/twurl:4
from /usr/bin/twurl:19:in `load'
from /usr/bin/twurl:19
    logout

Thanks a lot for your help!

08/26/2013 EDIT:

I have written a ruby script which should catch the error, but it seems the method "twurl" isn't recognized in the script, although when running "twurl... " directly on the instance (and not via a script) everything works..

execute_twurl.rb

begin
   twurl -t -d track=keyword -H stream.twitter.com /1.1/statuses/filter.json)
rescue Exception=>e
    e.inspect
end

called with filename.sh

   #!/bin/sh

    #Connect to Amazon EC2
    ssh -i ~/.ssh/research.pem [email protected] ruby execute_twurl.rb

gives Error:

execute_twurl.rb:2: syntax error, unexpected tUMINUS, expecting kDO or '{' or '('
   twurl -t -d track=keyword -H stre...
             ^
execute_twurl.rb:2: syntax error, unexpected tIDENTIFIER, expecting kDO or '{' or '('
...track=keyword -H stream.twitter.com /1.1/statuses/fil...
                              ^
execute_twurl.rb:2: unknown regexp options - tat
execute_twurl.rb:2: syntax error, unexpected ')', expecting kEND

Write a Ruby script that will make use of twurl. There you can write your custom rescue handling. — Konrad Reiche
– Konrad Reiche, Commented Aug 25, 2013 at 19:08
Is the ruby script yours? Because to catch a ruby exception you either have to rewrite the twurl code, or you have to write a ruby program that executes the twurl program and then catches the exception thrown by twurl. You can't catch a ruby exception in a shell script. You can certainly check the exit status of the ssh command in your shell script and re-execute your shell command if the remote command failed. — 7stud
– 7stud, Commented Aug 26, 2013 at 1:43
The twurl code is not from me - that's the point. Thanks for the hint! — yumba
– yumba, Commented Aug 26, 2013 at 12:37

Erica Tripp · Accepted Answer · 2013-09-06 09:00:07Z

3

to run system commands within ruby, you can do the following:

system 'twurl -t -d track=keyword -H stream.twitter.com /1.1/statuses/filter.json'

this gives you the global variable $? for the exit status of the process which should be 0 if the process didn't succeed. so your ruby script would be something like:

system 'twurl -t -d track=keyword -H stream.twitter.com /1.1/statuses/filter.json'
if $? == 0
   #retry, throw exeption, etc. 
end

you can also use backticks to run the command and get output status. the following may work for the timeout error.

output=`twurl -t -d track=keyword -H stream.twitter.com /1.1/statuses/filter.json` ;
result=$?.success?

edited Sep 6, 2013 at 9:00

answered Aug 27, 2013 at 6:35

Erica Tripp

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2 Comments

yumba Over a year ago

Your idea would be perfect but it doesn't work.. seems like $? isn't 0 when the execution expires and the timeout::error is thrown..

Erica Tripp Over a year ago

I added an option to use backticks that may solve your problem

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