I am using the following one liner to list the occurrences of combinations of `ATCG`, forming string of length 6. It works fine aside from not printing the occurrence of 0 matches. Is there a way to change the regex, or another part, to where it will print something like "0 ATTTAG"? 

```
#!/bin/bash
for file in e_coli.fa
do
    base=$(basename $file .fa)
    cat $file | perl -nE 'say for /(?<=([ATCG]{6}))/g' \
        | sort | uniq -c >> ${base}_hexhits_6mer.txt
done

stdout:
    465 AAAAAA
    607 AAAAAC
    661 AAAAAG
    581 AAAAAT
    563 AAAACA
    807 AAAACC
    770 AAAACG
    373 AAAACT
    663 AAAAGA
   1213 AAAAGC

```