How to make the input file of my program start from the 3rd line?

Question

I have a program that reads data from a file in this way

root@root# myprogram < inputfile.txt

Now I want my program to read the input file from the 3rd line and not from the beginning of the file.

I have to use < inputfile.txt. I can not call with pipe because of variable scope issues

Is there a way to do that in Linux?

Answer 1

Maybe this will work for you (process substitution):

program < <(sed -n '3,$p' inputfile.txt)

Answer 2

You can use tail:

tail -n +3 inputfile.txt | myprogram

In bash, you can also use

myprogram < <(tail -n +3 inputfile.txt)

Answer 3

Pure shell, no extra processes:

{ read -r; read -r; program; } < inputfile.txt

The first two calls to read each consume a line of input from input file.txt, so that they are not seen by program.

---

You can generalize this to skip the first $n lines of input.

{ 
  while [ "$((i++))" -lt "$n" ]; do read -r; done
  program
} < inputfile.txt

This becomes a little more readable with the use of some bash extensions:

{ while (( i++ < n )); do read -r; done; program; } < inputfile.txt

Answer 4

try this command: sed -n '3,$p' inputfile.txt | myprogram