sub g {blah}

print "Closest value is ",g(@list,$number);
# or
print "Closest value is ",g($number,@list);
# or
print "Closest value is ",g(\@list,$number);
# or
print "Closest value is ",g($number,\@list);
# OR
print "Closest value is ",$list[g(@list,$number)];
# or
print "Closest value is ",$list[g($number,@list)];
# or
print "Closest value is ",$list[g(\@list,$number)];
# or
print "Closest value is ",$list[g($number,\@list)];