Jenkins on Linux build (from Execute Shell read file and write a file)

be able to give me the instructions of what is needed from "EXECUTE SHELL" in a Jenkins job. You will test on your Jenkins and provide to me instructions,. check if a number 1234 exists in a file Yes or No or 0 or 1? add a record to a file - this is the layout field one mynumber field two mystring file contents will be like this 1234 mystring is here 2234 mystring is this 3234 mystring is that 4234 mystring is other 4235 mystring is thing