#!perl -w
use strict;

my %semanal;

while (<DATA>) {
    chomp;
    foreach my $letra (split //) {
        $semanal{$letra}++;
    }
}

foreach my $pal (sort keys %semanal) {
    print "$pal\t$semanal{$pal}\n";
}


__DATA__
lunes
martes
miercoles
jueves
viernes
sabado
domingo



output:

a   3
b   1
c   1
d   2
e   8
g   1
i   3
j   1
l   2
m   3
n   3
o   4
r   3
s   6
t   1
u   2
v   2