$ perl -le 'open F, "gobbledegook" or print "WARN1: $!"; print "PRINT: $!"; readlink "test" or print "WARN2: $!";  print "PRINT: $!'
WARN1: No such file or directory
PRINT: No such file or directory
WARN2: Invalid argument
PRINT: Invalid argument

##</code><code>##

$ perl -e 'print "BANG: $!"'
BANG:

$ perl -Mstrict -e 'print "BANG: $!"'
BANG: Bad file descriptor