Hello Julia, I guess I have understood you correctly. If I had to do it, I would have done like this. Read the text file and explode it from the two points (start of line 20 and end of line 40), using the explode() function. Then between the 2 exploded arrays insert what I wanted to. Hope this replies your question, but if not, do let me know.
Regards
T. A. Barry
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