Thank for your answer.
I think I have expressed myself badly.
What I meant was that i want to read inside the file ( Ligne 5 or Ligne 6 inside, for example) not the name of my file.
In my case I don't know which line is my string : "Infected files: " + a number .
I got NRPE and NSCP install
But i want to read inside the file to found a string : "Infected files: " + a number
If this number is 0 it s OK else Critical
Then i'am back to the beginning