For more on perl's grep try typing

perldoc -f grep

at your command prompt.

For more on your system grep... well, you'll have to consult man or some other system help.

Update below.

Your code is coming along nicely, but the highly verbose output may be (for a guess) why you want to consider grep.

As written, it will spit out the 'not found' message for each line lacking "icecream" as well as correctly acknowledging those lines where the search pattern exists. There are a couple ways around this.

• slurp (use search here) the entire file, if it's not too big for available RAM; concatenate the lines and search them
• Omit the else (considered bad form in an if clause by some... and won't tell you when the file contains no instances of icecream, unless you add some additional code -- say, making the else clause set a flag which you read only after the entire file has been scanned.

There are, of course, many other ways to do this, but exploring those ideas should be useful in the long run.