[dan-robertson]

Grep is fast. Like obviously in this case you’re ‘just’ measuring how fast you can read from a pipe, but there are plenty of ways grep could have been implemented that would have been slower. Generally, I think grep will convert queries into a form that can be searched for reasonably efficiently (eg KMP for longer strings (bit of a guess – not sure how good it is on modern hardware), obviously no backtracking for regular expressions.

[burntsushi]

I don't think KMP has been used in any practical substring implementation in ages. At least I'm not aware of one. I believe GNU grep uses Boyer-Moore, but that's not really the key here. The key is using memchr in BM's skip loop.