#!/usr/bin/env bash

# @(#) s1       Demonstrate combinations of 2 from list of strings in file.

# Utility functions: print-as-echo, print-line-with-visual-space, debug.
# export PATH="/usr/local/bin:/usr/bin:/bin"
LC_ALL=C ; LANG=C ; export LC_ALL LANG
pe() { for _i;do printf "%s" "$_i";done; printf "\n"; }
pl() { pe;pe "-----" ;pe "$*"; }
em() { pe "$*" >&2 ; }
db() { ( printf " db, ";for _i;do printf "%s" "$_i";done;printf "\n" ) >&2 ; }
db() { : ; }
C=$HOME/bin/context && [ -f $C ] && $C combination my-columns head tail

FILE=${1-data1}

pl " Input data file $FILE, columnized:"
my-columns $FILE

pl " Results:"
combination 2 $( cat $FILE ) |
tee f1 |
head -3
pe "..."
tail -3 f1

exit 0

$ ./s1

Environment: LC_ALL = C, LANG = C
(Versions displayed with local utility "version")
OS, ker|rel, machine: Linux, 3.16.0-4-amd64, x86_64
Distribution        : Debian 8.4 (jessie) 
bash GNU bash 4.3.30
combination (local) 1.1
my-columns (local) 1.3
head (GNU coreutils) 8.23
tail (GNU coreutils) 8.23

-----
 Input data file data1, columnized:
Black Blue Brown Orange Red Yellow Green White Purple Silver Grey Tan

-----
 Results:
Black Blue
Black Brown
Black Orange
...
Silver Grey
Silver Tan
Grey Tan

perl -w -e '
BEGIN { @a = @ARGV }
use Math::Combinatorics;
print join( "\n", map { join " ", @$_ } combine( 2, @a ) ),
"\n";' $( cat $FILE )