Just use two regexen, and consider a match successful only if the first regex matches but the second doesn’t. For example, to match sequences containing only letters, digits, and hyphens, but not containing all digits:

#! perl
use strict;
use warnings;

my $re1 = qr{ ^ [\w-]+ $ }x;
my $re2 = qr{ ^  \d+   $ }x;

while (<DATA>)
{
    chomp;
    printf "%s : %s\n", $_, /$re1/ && !/$re2/ ? 'yes' : 'no';
}

__DATA__
foo
1foo
foo2
3foo4
foo5bar
87
foo-bar
foo42-baz
foo17@12
[download]

Output:

17:03 >perl 950_SoPW.pl
foo : yes
1foo : yes
foo2 : yes
3foo4 : yes
foo5bar : yes
87 : no
foo-bar : yes
foo42-baz : yes
foo17@12 : no

17:04 >
[download]

Hope that helps,