Bash Implementation of B.R. Heaps' Permutation Algorithm

#!/bin/bash 

  ######################################################################
 ######################################################################
## Author: Adam Michael Danischewski 
## GitHub: https://github.com/AdamDanischewski/hpermutate
## Created Date: 2019-11-08
## Name: hpermutate.bsh 
## Version: v0.00
## Last Modified: 2019-11-08
## Issues: If you find any issues emai1 me at <my first name> (dot) 
##         <my last name> (at) gmail (dot) com. 
## 
## This is a Bash implementation of Heap's algorithm which generates all 
## possible permutations of n objects, as first proposed by B. R. Heap 
## in 1963. Speed is reasonable for a recursive shell script. 
##
## This program is distributed in the hope that it will be useful,
## but WITHOUT ANY WARRANTY; without even the implied warranty of
## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  
##
## Released under Creative Commons License: CC BY-SA 4.0
## https://creativecommons.org/licenses/by-sa/4.0/
 ######################################################################
  ######################################################################
_=$BASH_ARGC
OLDIFS=$IFS 

declare    arr=""
declare -i length=0

## Arg 1 - index 1: First swap index
## Arg 2 - index 2: Second swap index
function swap() { 
 local -a my_array 
 local    tmpval="" 
 local -i index1=${1} 
 local -i index2=${2}  
 OLDIFS=$IFS
 IFS=" " read -ra my_array <<< "${arr}"
 tmpval=${my_array[${index1}]}
 my_array[${index1}]=${my_array[${index2}]}
 my_array[${index2}]=${tmpval}
 IFS=$OLDIFS
 arr="${my_array[@]}"
}

## Arg1 - Integer: size
function heappermutation() { 
 local -i size=${1}
 local -i i=0
 if((${size}==1)); then  
  echo "${arr}"
  return
 fi 
 for((i=0;i<${size};i++)) { 
  heappermutation $((${size}-1)) 
  if(((${size}%2)==1)); then    
   swap 0 $((${size}-1))
  else 
   swap ${i} $((${size}-1))
  fi 
 } 
}

function init() { 
 arr="${BASH_ARGV[@]}"
 length=${BASH_ARGC}
}

function main() { 
 init 
 heappermutation ${length}
} 

if(($#<1))||[[ "${1}" =~ ^- ]]; then 
cat<<EOF 

Usage: ${0##*/} <args=eg. 1 2 3 4 5>
 
 Eg. $> ${0##*/} 1 2 3 
        3 2 1
        2 3 1
        1 3 2
        3 1 2
        2 1 3
        1 2 3
EOF
 exit 1
fi

main
exit 0

Get the latest, replete with an iterative algorithm, on GitHub.