$ perl -v

This is perl, version 5.005_03 built for sun4-solaris

Copyright 1987-1999, Larry Wall

...

$ perl -le '$_="abc"; print "ok" if (/^[[:ascii:]]+$/)'

# (no output -- that char.class doesn't work)

$ perl -le '$_="abc"; print "ok" if (/^[\x00-\x7f]+$/)'
ok


##</code><code>##

$ perl5.8.0 -le '$_="abc"; print "ok" if (/^[[:ascii:]]+$/)'
ok