Question

I expected these values to match. They did not match when the shell script exited due to some error condition (and thus returned a non-zero value). Shell $? returned 1, ruby $? returned 256.

>> %x[ ls kkr]
ls: kkr: No such file or directory
=> ""
>> puts $?
256
=> nil
>> exit
Hadoop:~ Madcap$ ls kkr
ls: kkr: No such file or directory
Hadoop:~ Madcap$ echo $?
1 

Answer 1

In Ruby $? is a Process::Status instance. Printing $? is equivalent to calling $?.to_s, which is equivalent to $?.to_i.to_s (from the documentation).

to_i is not the same as exitstatus.

From the documentation:

Posix systems record information on processes using a 16-bit integer.
The lower bits record the process status (stopped, exited, signaled)
and the upper bits possibly contain additional information (for
example the program’s return code in the case of exited processes).

$?.to_i will display this whole 16-bit integer, but what you want is just the exit code, so for this you need to call exitstatus:

$?.exitstatus