The most efficient, in terms of moving the task frrom the to-do list to the done list, is:

# at the Unix command line:
$ find $dir -type f -exec grep 'foo bar baz' {} > /dev/nul \; -print
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Search recurcively below the directory $dir, and if a found object is a file, grep for the constant string, 'foo bar baz'; Send the output to dev null, we only want to know if the text was foujnd. If it was, ,print the name of the file.