I just found a case where grep and git grep yield different results. Inside the ixgbe directory of the Linux kernel I did:

$ grep enter_lplu *.[ch]

And got the following:

ixgbe_main.c:	if (adapter->hw.phy.ops.enter_lplu) {
ixgbe_main.c:		adapter->hw.phy.ops.enter_lplu(&adapter->hw);
ixgbe_type.h:	s32 (*enter_lplu)(struct ixgbe_hw *);
ixgbe_x550.c:/** ixgbe_enter_lplu_x550em - Transition to low power states
ixgbe_x550.c:static s32 ixgbe_enter_lplu_t_x550em(struct ixgbe_hw *hw)
ixgbe_x550.c:			phy->ops.enter_lplu = ixgbe_enter_lplu_t_x550em;

But when I did:

$ git grep enter_lplu

I got:

ixgbe_main.c:   if (adapter->hw.phy.ops.enter_lplu) {
ixgbe_main.c:           adapter->hw.phy.ops.enter_lplu(&adapter->hw);
ixgbe_type.h:   s32 (*enter_lplu)(struct ixgbe_hw *);
ixgbe_x550.c:/** ixgbe_enter_lplu_x550em - Transition to low power states
ixgbe_x550.c:static s32 ixgbe_enter_lplu_t_x550em(struct ixgbe_hw *hw)

You can see that git grep missed the line in ixgbe_x550.c that had two hits on the string.

This was with git 2.1.0 in Fedora 21. I use git grep a lot and never noticed a problem before. I just updated my Fedora 21 system yesterday, so I have to figure that has something to do with it. I checked and git didn't get updated, so I figure it must be a library that is really broken.

I see in my update log that pcre was updated to:

pcre.x86_64 0:8.35-12.fc21
pcre-devel.x86_64 0:8.35-12.fc21

Yet the grep command is unaffected.

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Mark Rustad, Networking Division, Intel Corporation