Standard grep is much faster on multi-gigabyte files than anything you can figure out how to do in your pet language. By the time you get close to matching grep, you would have reimplemented most of grep, in half-assed fashion at that.
Your delusion is assuming standard command line tools are simple in function because they have a simple interface that Average Joe can use.
One liner shell commands often turn complicated quickly.
But has too many weird quirks that it can replace grep for data munging. E.g.
$ ag verb fullform_nn.txt >/tmp/verbs
ERR: Too many matches in fullform_nn.txt. Skipping the rest of this file.
$ grep -c verb fullform_nn.txt
206077
$ ag --max-count 206077 verb fullform_nn.txt >/tmp/verbs
ERR: Too many matches in fullform_nn.txt. Skipping the rest of this file.
Have you rerun your tests in the "C" locale?