Search Text File For String

I am needing to search a text file and paras a line of text but have been unsuccessful. I have read the sdk for using the different methods like left, right, mid and even the ifRegex but with no positive results. I know the particular string of text but the location in the text file may vary. The text file could contain up to 130 lines. Once I am able to find the particular string I could use the left, right to extract the desired string. Can somebody tell me the easiest way to search the file for string.
Thanks for any help

The file is a tmp file on the roku.

BrightScript Debugger> ? inStr(1, "some really big string coming from a file perhaps", "ring")
 19

See 8.5 Instr(start as Integer, text as String, substring as String) as Integer
Also 7.7 ReadAsciiFile(filepath as String) as String

Thanks, was able to locate string with your help using instr.