$ perl -MO=Deparse -e 's/http://example.com/[404 Not Found]/g'
Bareword found where operator expected at -e line 1, near "404 Not"
	(Missing operator before Not?)
Regexp modifiers "/a" and "/l" are mutually exclusive at -e line 1, at end of line
syntax error at -e line 1, near "404 Not Found"
-e had compilation errors.