ruby system command check exit code

Question

I have a bunch of system calls in ruby such as the following and I want to check their exit codes simultaneously so that my script exits out if that command fails.

Answer 1

From the documentation:

system returns true if the command gives zero exit status, false for non zero exit status. Returns nil if command execution fails.

system("unknown command")     #=> nil
system("echo foo")            #=> true
system("echo foo | grep bar") #=> false

Furthermore

An error status is available in $?.

system("VBoxManage createvm --invalid-option")

$?             #=> #<Process::Status: pid 9926 exit 2>
$?.exitstatus  #=> 2

Answer 2

system returns false if the command has an non-zero exit code, or nil if there is no command.

Therefore

system( "foo" ) or exit

or

system( "foo" ) or raise "Something went wrong with foo"

should work, and are reasonably concise.

Answer 3

One way to do this is to chain them using and or &&:

system("VBoxManage createvm --name test1") and system("ruby test.rb")

The second call won't be run if the first fails.

You can wrap those in an if () to give you some flow-control:

if (
  system("VBoxManage createvm --name test1") && 
  system("ruby test.rb")
) 
  # do something
else
  # do something with $?
end

Answer 4

For me, I preferred use `` to call the shell commands and check $? to get process status. The $? is a process status object, you can get the command's process information from this object, including: status code, execution status, pid, etc.

Some useful methods of the $? object:

   $?.exitstatus => return error code    
   $?.success? => return true if error code is 0, otherwise false
   $?.pid => created process pid

Answer 5

You're not capturing the result of your system call, which is where the result code is returned:

exit_code = system("ruby test.rb")

Remember each system call or equivalent, which includes the backtick-method, spawns a new shell, so it's not possible to capture the result of a previous shell's environment. In this case exit_code is true if everything worked out, nil otherwise.

The popen3 command provides more low-level detail.