ruby system command check exit code

问题:

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.

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

I want something like

system("VBoxManage createvm --name test1", 0) <-- where the second parameter checks the exit code and confirms that that system call was successful, and if not, it'll raise an error or do something of that sort.

Is that possible at all?

I've tried something along the lines of this and that didn't work either.

system("ruby test.rb")
system("echo $?")

or

`ruby test.rb`
exit_code = `echo $?`
if exit_code != 0
  raise 'Exit code is not zero'
end

回答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

回答2:

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

回答3:

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.

回答4:

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.

回答5:

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