UPDATED: I just remove "case insensitive" as default and now I got better results (https://github.com/golang/go/issues/13288)

Not "lot faster", but, some faster :).

For instance, search for pattern "better" in project repo:

_grep_

---------------------------------------------------------

$ time grep better -rn *

...

0.04 real 0.03 user 0.00 sys

---------------------------------------------------------

_sif_

---------------------------------------------------------

$ time sif better

...

0.01 real 0.00 user 0.00 sys

---------------------------------------------------------

_ack_

---------------------------------------------------------

$ time ack better

...

0.10 real 0.06 user 0.01 sys

---------------------------------------------------------

_ag_

---------------------------------------------------------

$ time ag better

...

0.01 real 0.00 user 0.00 sys

---------------------------------------------------------

I'll try to make tests with goroutines in next week's