Finding gaps in sequential numbers

Question

I don’t do this stuff for a living so forgive me if it’s a simple question (or more complicated than I think). I‘ve been digging through the archives and found a lot of tip

Answer 1

Given input file, use the numinterval util and paste its output beside file, then munge it with tr, xargs, sed and printf:

gaps() { paste  <(echo; numinterval "$1" | tr 1 '-' | tr -d '[02-9]') "$1" | 
         tr -d '[:blank:]' | xargs echo | 
         sed 's/ -/-/g;s/-[^ ]*-/-/g' | xargs printf "%s\n" ; }

Output of gaps file:

5-8
15-17
25-27

---

How it works. The output of paste <(echo; numinterval file) file looks like:

    5
1   6
1   7
1   8
7   15
1   16
1   17
8   25
1   26
1   27

From there we mainly replace things in column #1, and tweak the spacing. The 1s are replaced with -s, and the higher numbers are blanked. Remove some blanks with tr. Replace runs of hyphens like "5-6-7-8" with a single hyphen "5-8", and that's the output.