Could not execute shell commands in sequence in Ruby script

Question

I have to execute simple shell commands in ruby script one after other. Mys script does the following things in order: check if ABC services running, if true then stop_services; delete directories; copy fresh directories from src to dest. Below is the code:

def stop_ABC_services
     begin
       ABC_service_cnt = "ps -fu #{user} | grep ABC  | grep -v grep | wc -l"

       while exec "#{ABC_service_cnt } >& ABC.log".to_i > 0
           exec "sh stop_ABC.sh stop >>& ABC.log"
       end

     rescue => e
          puts "Error occured in stop_siebel_services - #{e}.".red
          Kernel.exit(false)
     end
end

But it is failing at the very first method stop_ABC_services by giving the following error: Error occured in stop_ABC_services - can't convert false into String. Cannot proceed further. Quitting...

I am not able to figure out the solution for this. Appreciate the guidance to fix this.

Thanks

Well, remove your error handling or add puts e.backtrace to it and post full error message please. — EugZol
– EugZol, Commented Aug 17, 2015 at 15:37
You probably meant while exec("#{ABC_service_cnt } >& ABC.log").to_i > 0 — Sergio Tulentsev
– Sergio Tulentsev, Commented Aug 17, 2015 at 16:10
Note that exec, in accordance with the Unix system call of the same name, replaces the current process; it doesn't spawn a new one. This probably isn't what you want. — Ajedi32
– Ajedi32, Commented Aug 17, 2015 at 16:20
Instead of exec and the quotes, use the `<command> ` syntax. It's that button above the ~. I think exec ends the process after it executes that command. — Charles
– Charles, Commented Aug 17, 2015 at 23:21

Sergio Tulentsev · Accepted Answer · 2015-08-17 16:21:47Z

1

Short answer: use parentheses (and don't use exec).

Longer answer: by not using parentheses you make ruby execute code in an order completely different from what you want. This

exec "#{ABC_service_cnt } >& ABC.log".to_i > 0

is executed in this sequence

"#{ABC_service_cnt } >& ABC.log".to_i # => 0
0 > 0 # => false
exec false # => TypeError: no implicit conversion of false into String

Should be this instead

while exec("#{ABC_service_cnt } >& ABC.log").to_i > 0

Also you might want not to use exec because it replaces the current process. Meaning, your while (and everything inside/after it) will not get a chance to run even once. Most likely you want system() call, which also handles zero/non-zero exit codes.

edited Aug 17, 2015 at 16:21

answered Aug 17, 2015 at 16:16

Sergio Tulentsev

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1 Comment

itsh Over a year ago

Thank you, adding parenthesis helped in fixing the problem.

Community · Accepted Answer · 2017-04-13 12:36:28Z

0

You could do that only executing sh

system("ps aux | grep ABC | grep -v grep  && stop_ABC.sh stop >>& ABC.log")

The meaning of that is.

&& will run stop_ABC.sh stop >>& ABC.log if ps aux | grep ABC | grep -v grep

you could find more info here

edited Apr 13, 2017 at 12:36

CommunityBot

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answered Aug 17, 2015 at 15:58

Horacio

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Comments

itsh · Accepted Answer · 2015-08-17 19:16:05Z

0

def stop_ABC_services
 begin
   ABC_service_cnt = "ps -fu #{user} | grep ABC  | grep -v grep | wc -l"

   while exec("#{ABC_service_cnt } >& ABC.log").to_i > 0
       exec "sh stop_ABC.sh stop >>& ABC.log"
   end

 rescue => e
      puts "Error occured in stop_ABC_services - #{e}.".red
      Kernel.exit(false)
 end
end

answered Aug 17, 2015 at 19:16

itsh

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