UPDATE! Oops!! I were wrong...

I didn't take care of
$a=~'a' is correct
I thought that it would be
$a=~m'a' instead
But

perl -e "$a='b}b';print 'Mached!' if $a=~'}'"
[download]

runs as expected.

It's not necessary the backslash in '{'
Update In response to drinkd post, I've to say that both

perl -e "$a='b}b';print 'Mached!' if $a=~'}'"
perl -e "$a='b}b';print 'Mached!' if $a=~'}'"
[download]

are correct. I don't have to write backlashes.
Hopes