Including text from other files

Use the m4 tool, the gnu macro processor, to
process an include file.
To include a file in a text file, specify the file
to be included on a line of its own, like this:
include(file)

Example

m4 menu > monday.txt

menu file

Diner Menu for Today
Soups
-----
include(soups)
Sandwiches
----------
include(sandwiches)

sandwiches file

BLT
Ham on Rye
Roast Beef

soups file

Clam Chowder
Lobster Bisque
Vegetable

monday.txt file

Diner Menu for Today
Soups
-----
Clam Chowder
Lobster Bisque
Vegetable
Sandwiches
----------
BLT
Ham on Rye
Roast Beef