Find a String in Text File
findstr /c:YourStringHere FileNameHere.txt && Echo TRUE || Echo FALSE
* you can change the echos to subroutines, and make this pretty powerful
Compare Two Files
The fastest method to diff two files is to use findstr command. It will compare and return the result to a new file.
findstr /vixg:C:\FILE1.txt C:\FILE2.txt > C:\FILE3.txt
Notes
/v : Prints only lines that do not contain a match.
/i : Specifies that the search is not to be case-sensitive.
/x : Prints lines that match exactly.
/g: file : Gets search strings from the specified file.