Returns tokens that contain the specified string.
Note that if you specify zero for N, it returns the total number of matching tokens.
echo -ag $matchtok(This is a test, is, 0, 32)
This example returns 2, as the string This is a test contains is two times (This and is).
echo -ag $matchtok(This is a test, is, 1, 32)
This example returns This as it's the first string containing is.