my @list = grep /\btest\b/, <DATA>;
chomp @list;
print "$_\n" foreach @list;

__DATA__
This is only a test.
Here's a line that doesn't contain the trigger text.
This line contains test and test again.
Now you see it, now you don't.
Testing one two three.
Test or not to test?
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This passes a filehandle to grep, along with a simple regexp that tells it to find only those lines that contain the word "test" (rejecting words like 'testing').

For matches across multiple lines you have to set the $/ special variable to paragraph or slurp mode and use an /s modifier on your regexp.