Shell Programming and Scripting

#!/bin/bash

ret_int()
{
  arg=$1
  num=$(echo $arg | sed 's/[^0-9]//g')
  alp=$(echo $arg | sed 's/[^A-Z]//g')
  alphnum=$(echo $alp | sed 'y/ABCDEFG/1234567/')
  return ${num}${alphnum}
}

read val < infile
val=$(echo $val | sed 's/,/ /g')

for i in $val
do
   ret_int $i
   a[$?]=$i
done

printf "\tA\tB\tC\tD\tE\tF\tG\n"
for i in $(seq 1 7)
do
  printf $i
  for j in $(seq 1 7)
  do
    test ! -z "${a[$i$j]}" && val="X" || val=""
    printf "\t$val"
  done
  echo
done

#!/bin/bash
read val < infile
val=$(echo $val | sed 's/,/ /g')

for i in $val
do
   co=$(echo $i | sed 'y/ABCDEFG/1234567/')   
   a[$co]=$i
done
    
printf "\tA\tB\tC\tD\tE\tF\tG\n"
for i in $(seq 1 7) 
do  
  printf $i
  for j in $(seq 1 7)
  do
    test ! -z "${a[$j$i]}" && val="X" || val=""
    printf "\t$val"
  done
  printf "\n"
done

ret_int $i
a[$?]=$i

co=$(echo $i | sed 'y/ABCDEFG/1234567/')
a[$co]=$i

#!/bin/bash

ret_int() #creating of function
{
 
  #creating a variable with value of the First argument parse in Shell
  #In this case, what will be value of $1?
  arg=$1
 
  #creating an array (What's this array for?)
  num=$(echo $arg | sed 's/[^0-9]//g')
 
  #creating an array (What's this array for?)
  alp=$(echo $arg | sed 's/[^A-Z]//g')
 
  #creating an array (What's this array for?)
  alphnum=$(echo $alp | sed 'y/ABCDEFG/1234567/')
  return ${num}${alphnum}
}

#creating a variable that read file "infile"
read val < infile
 
#creating an array to store the data in "infile" and convert all "," to " "
val=$(echo $val | sed 's/,/ /g')

#I don't understand this part
for i in $val
do
   ret_int $i
   a[$?]=$i
done

#printing A-G with a tab spacing
printf "\tA\tB\tC\tD\tE\tF\tG\n"

#I don't understand this part
for i in $(seq 1 7)
do
  printf $i
  for j in $(seq 1 7)
  do
    test ! -z "${a[$i$j]}" && val="X" || val=""
    printf "\t$val"
  done
  echo
done