Of course, I can't say that mine is much clearer in that regard.
It isn't. I felt ickier the more I looked at that code for handling params too.
There is no reason to try to differentiate between undef and the empty string in this case. Interpolated, printed, or otherwise stringified, undef is an empty string. So,
# Cargo-cultish version with a temp variable.
my $_name = param('name') || '';
my ($name) = $_name =~ /^([[:alpha:]]+)$/;
is equivalent to
# BrowserUk's cargo-cultish only version.
my ($name) = (param('name') || '') =~ /^([[:alpha:]]+)$/;
which is also equivalent to
# My preferred version.
my ($name) = param('name') =~ /^([[:alpha:]]+)$/;
Using the construct param('name') || '' at all is questionable. It throws away information. CGI returns an empty string in the case that the parameter was submitted with no value and undef in the case that it wasn't submitted at all. If you need to differentiate between those cases then you can check for undef. If you don't need to, you can ignore the difference (as above.)
"My two cents aren't worth a dime.";