ruby - How does the command-line option "W1" differ from "W0"? -

ruby - How does the command-line option "W1" differ from "W0"? -

from within ruby script, verbosity can tested value of $verbose global variable, can have 3 states:

nil in case verbosity level “0” (silence) false level “1” (medium); default true level “2” (verbose); verbose mode.

i started play code understand difference between them:

@ubuntu:~$ ruby -w0 -e 'a=10;a=10;@foo' @ubuntu:~$ ruby -w1 -e 'a=10;a=10;@foo' @ubuntu:~$ ruby -w2 -e 'a=10;a=10;@foo' -e:1: warning: perchance useless utilize of variable in void context -e:1: warning: instance variable @foo not initialized @ubuntu:~$

but not understand difference between w1 , w0. help me understand difference?

to see real difference, have print text on $stderr. i've made next alter on example:

ruby -w0 -e 'a=10;a=10;@foo;warn "hello"'

note running code w0 flag, nil appear in terminal when execute. now, if run w1, see "error" message generated kernel#warn:

ruby -w1 -e 'a=10;a=10;@foo;warn "hello"'

and finally, w2 show error , warnings generated interpreter.

ruby ruby-1.9.3