This is not a Perl question, and
you aren't very clear on what you mean by
changing the font. If you mean changing the
font face, it depends upon your terminal.
I believe it is possible for certain ancient
terminals, and emulators of those terminals.
If you mean changing the weight... if you
send your output through less a sequence like
c^Hca^Hat^Ht
Will show as
cat (cat in bold).
You can output backspace
^H using
\b
print "c\bca\bat\bt\n"
--
I'm not belgian but I play one on TV.