cjkim,
There are two possibilities that I can think of:
- M is a filehandle
- M should have been a little m
In the first case,
print M "foo" would have printed "foo" to the file that M was opened to. It does not make any sense by itself (without the print), so it is very unlikely that this is what you mean.
In the second case, it is used to change the delimiters of a regex. Typically used to get rid of the leaning toothpick problem.
print "matched" if /\/foo\/bar\/index\.html/;
# vs
print "matched if m"foo/bar/index\.html";