What's with the idea you have to write the solution in a single line of code?
This can be done easily with a few lines of code, why write it in a single line? Are you running with 8MB of ram or something?
1. Open the file IO in read write mode.
2. Read the file into an array.
3. Set up a good old fashioned boolean $foundString
4. Traverse the array til the boolean is true printing stuff to the file.
5. Boolean is true close the file..DONE.
Why not? I never said you have to... Feel free to write as many lines as makes you feel comfortable. I just happen to like one-liners for tasks like these — which doesn't imply anyone else would have to like or use them, too. Yet others like golfing. Just for the fun of it...