Generate all possible dual combinations of file [BASH] - bash

Question

I'm trying to generate all possible dual combinations (in my case, of files) with the following script taken from here:
function get_combs(A,B, i,n,comb) {
n = length(A)
if (r=="") r = 2
comb = ""
for (i=1; i <= r; i++) {
indices[i] = i
comb = (i>1 ? comb OFS : "") A[indices[i]]
}
B[comb]
while (indices[1] < n - r + 1) {
for (i = r; i >= 1; i--) {
if (indices[i] < n - r + i) {
indices[i]++
p = i
break}}
for (i = p + 1; i <= r; i++) indices[i] = indices[i - 1] + 1
comb = ""
for (i=1; i <= r; i++) {
comb = (i>1 ? comb OFS : "") A[indices[i]]
}
B[comb]
}
}
{ A[NR] = $0 }
END {
OFS = "\t"
for (r=NR; r>=2; r--) {
delete B
get_combs(A,B)
PROCINFO["sorted_in"] = "#ind_str_asc"
for (comb in B) {
print comb
}
}
}
Everything works nice but it's generating all combos, not only the dual ones:
$ awk -f combos.awk <(ls *pileup)
348-34_control_MO.sorted.bam.pileup 577_MO.sorted.bam.pileup 822_MO1.sorted.bam.pileup
348-34_control_MO.sorted.bam.pileup 577_MO.sorted.bam.pileup
348-34_control_MO.sorted.bam.pileup 822_MO1.sorted.bam.pileup
577_MO.sorted.bam.pileup 822_MO1.sorted.bam.pileup
I'd like something like that:
348-34_control_MO.sorted.bam.pileup 577_MO.sorted.bam.pileup
348-34_control_MO.sorted.bam.pileup 822_MO1.sorted.bam.pileup
577_MO.sorted.bam.pileup 822_MO1.sorted.bam.pileup
Thanks a lot.

Answer 1

Sample input to simulate ls *pileup:
$ cat ls.out
577_MO.sorted.bam.pileup
348-34_control_MO.sorted.bam.pileup
822_MO1.sorted.bam.pileup
One awk approach:
awk '
BEGIN { OFS="\t" }
{ A[NR]=$0 }
END { for (i=1;i<NR;i++)
for (j=i+1;j<=NR;j++)
print A[i],A[j]
}
' <(sort -V ls.out)
NOTE: in OP's case the sort -V ls.out would be replaced with ls *pileup | sort -V (or whatever sort options are appropriate)
This generates:
348-34_control_MO.sorted.bam.pileup 577_MO.sorted.bam.pileup
348-34_control_MO.sorted.bam.pileup 822_MO1.sorted.bam.pileup
577_MO.sorted.bam.pileup 822_MO1.sorted.bam.pileup