Question

I have the following shell script code. Here if I’m using NR==$i in gawk statement, it doesn’t work, while if I simply use NR==1 (or some other integer value) it works perfectly fine.

for ((i=1;i<=5;i++))
 do
    gawk 'NR==$i{//some action}' input.txt
done

Can anyone please let me know what is the issue here?

Answer 1

The problem is that the single quotes around the awk script mean that bash does no substitution inside the string and gawk sees literally $i (which is the same as $0 since i is not initialized in the gawk script).

This time, use double quotes instead:

for ((i=1;i<=5;i++))
do
    gawk "NR==$i{//some action}" input.txt
done

In general, it would probably be better to pass the variable explicitly:

for ((i=1;i<=5;i++))
do
    gawk -v i=$i 'NR==i{//some action}' input.txt
done