Shell Programming and Scripting

a b c d 
E F G H
....

a b
a c
a d
b c
b d
c d
E F
E G
E H
F G
F H
G H
..

import itertools
paralog = ['a','b','c','d']
for L in range(2, len(paralog)-1):
  for subset in itertools.combinations(paralog, L):
    print(subset)

awk '{for (i=1; i<=NF; i++) for (j=i+1; j<=NF; j++) print $i, $j}' file
a b
a c
a d
b c
b d
c d
E F
E G
E H
F G
F H
G H

import fileinput
import itertools

for line in fileinput.input():
    fields = line.split()
    for L in range(2, len(fields)-1):
        for subset in itertools.combinations(fields, L):
            print ' '.join(subset)

while(<>) {
    my @fields = split;
    while(@fields) {
        my $lead = shift @fields;
        for(@fields) {
            print "$lead $_\n";
        }
    }
}

$ 
$ cat list_comb.txt
a b c d
E F G H
$ 
$ perl -lne 'sub comb {return if !$#_;
                 print for glob join "", map "{$_}", map {join ",", @$_}([shift],\@_);
                 comb(@_)}
             comb(split)' list_comb.txt
ab
ac
ad
bc
bd
cd
EF
EG
EH
FG
FH
GH
$ 
$