WHAT MAKES YOU THINK IT DOES NOT AGREE WITH MY CONCLUSION THAT $a IS SIMPLY IGNORED, AND A WARNING IS PRINTED?

Well, we can rely on the declared principle that warnings do not change anything about the execution of the program. Other than additional output to STDERR (and in the absence of a $SIG{__WARN__}, which this program clearly does not have), a program will always run identically whether warnings are on or off. Warnings do not change program execution flow. They merely turn on additional debugging output.

Second, we can test whether print actually "printed" in two ways. First, it'll return a true value indicating a "successful" print to an open filehandle with no I/O error. Second, we can alter something like $\ to add additional text to the print. I'm sure if you do either of those, you'll see that the undef was treated as the empty string, a warning was sent to STDERR, and the print completed its task. The print was not aborted.

-- Randal L. Schwartz, Perl hacker
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