--line-regexp option with null data

问题:

Consider this command:

printf 'alpha\nbravo\ncharlie\n' | grep --line-regexp --quiet bravo

grep sees 3 lines separated by newline, and matches the bravo line. Now consider this command:

printf 'alpha\0bravo\0charlie\0' | grep --line-regexp --quiet bravo

My thinking tells me that because I have not used --null-data, grep should see 1 or even 0 lines separated by newline, and fail to match a bravo followed by newline. However it does not, it succeeds just like the first command, why is this?

回答1:

This behavior was introduced with Grep 2.21:

When searching binary data, grep now may treat non-text bytes as line terminators. This can boost performance significantly.

So what happens now is that with binary data, all non-text bytes (including newlines) are treated as line terminators. If you want to change this behavior, you can:

• use --text. This will ensure that only newlines are line terminators

• use --null-data. This will ensure that only null bytes are line terminators