Shell - Print values in a comma separated string

With bash you could do

ordinals=( first second third fourth fifth sixth )
n=0
while IFS=, read -ra cols; do
    echo "line $((++n))"
    for i in "${!cols[@]}"; do
        echo "${ordinals[i]} col=${cols[i]}"
    done
done < file

That reads the words in each line into an array named cols, then we interate over the indices of that array so we can correlate the value to the ordinal.

For the first 3 lines, we get

line 1
first col=abc
second col=def
third col=ghi
line 2
first col=abc
second col=ghi
line 3
first col=def
second col=abc
third col=ghi

Assuming that the input file only has at most three columns, the following uses a while-read loop to read the comma-separated values from standard input and outputs them in a format similar to what you showed:

#!/bin/sh

while IFS=, read -r first second third
do
    printf 'Line %d:\n' "$(( ++n ))"
    ${first:+printf 'First:\t%s\n' "$first"}
    ${second:+printf 'Second:\t%s\n' "$second"}
    ${third:+printf 'Third:\t%s\n' "$third"}
done

The parameter expansion ${variable:+word} expands to word if variable is set and non-empty. The code uses this to execute printf for output if the corresponding variable contains data to be printed.

Testing on the provided data:

$ ./script.sh <file
Line 1:
First:  abc
Second: def
Third:  ghi
Line 2:
First:  abc
Second: ghi
Line 3:
First:  def
Second: abc
Third:  ghi
Line 4:
First:  def
Second: abc
Line 5:
First:  abc
Second: def
Line 6:
First:  abc
Second: def
Third:  ghi