Add or Insert a Heading Extra Line after Every nth Line of File in Unix / Linux

Here is my input data file and see the output as per the requirements below.

cat inp.txt

clark            2450

king             5000

miller           1300

smith             800

jones            2975

scott            3000

adams            1100

1. Add extra line to every line

awk '{$0 = $0"\n"} 1' inp.txt

awk '{$0 = $0"\n"} { print }' inp.txt

clark            2450

king             5000

miller           1300

smith             800

jones            2975

scott            3000

adams            1100

2. Add Extra line after every 2 lines. You can change the value of 2 which is marked in red below as per your requirement. Suppose if you wanted to add a new line after 3 you can use 3 instead of 2 in below example.

awk '!( NR % 2) {$0 = $0"\n"} 1' inp.txt

or

awk '!( NR % 2) {$0 = $0"\n"} { print }' inp.txt

clark            2450

king             5000

miller           1300

smith             800

jones            2975

scott            3000

adams            1100

3. Add heading line every n lines

awk '!( NR % 2) {$0 = "Name             SAL\n---------------------\n"$0} 1' inp.txt

or

awk '!( NR % 2) {$0 = "Name             SAL\n---------------------\n"$0} { print }' inp.txt

clark            2450

Name             SAL

-------------------

king             5000

miller           1300

Name             SAL

-------------------

smith             800

jones            2975

Name             SAL

-------------------

scott            3000

adams            1100

4. Add Column titles to every lines

awk  '{print "Name: "$1 "\t Sal:" $2}' inp.txt

Name: clark      Sal:2450

Name: king       Sal:5000

Name: miller     Sal:1300

Name: smith      Sal:800

Name: jones      Sal:2975

Name: scott      Sal:3000

Name: adams      Sal:1100

You can achieve these goals using a lengthy shell script as below.

#!/bin/sh

cntr=0

while read line

    do

    ((chk=cntr%3))

    if [ "$chk" -eq 0 ]; then

        echo -e "\n$line"

    else

        echo "$line"

    fi

    ((cntr=cntr+1))

done < inp.txt