perl -Mstrict -Mwarnings  -MO=Deparse -e 'print M"xxxx";'
Name "main::M" used only once: possible typo at -e line 1.
print M 'xxxx';
-e syntax OK
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...or, in other words, the same thing that 'print STDOUT "xxxx"' does modulo the specific filehandle...what do *you* expect to happen when you print to the filehandle M? Is it open? Is it writable?