csh - Weird C-shell return code for evaluating 1-1 -

csh - Weird C-shell return code for evaluating 1-1 -

i doing in csh

set = `expr 1 - 1` echo $?

it sets it 0, error code returned 1. why error code not 0 if look evaluated correctly , reply set correctly?

on other hand if had

set = `expr 2 - 1` echo $?

then error code 0. problem evaluating 1-1?

because expr weird. same happens look evaluates zero.

quoting man page:

exit status 0 if look neither null nor 0, 1 if look null or 0, 2 if look syntactically invalid, , 3 if error occurred.

shell arithmetic preferable.

@ = 1 - 1 echo $? : $it 0 : 0

shell csh