The other interesting question is what algorithm we use to find the pattern
in each line.
Generally bytes.Contains uses Rabin-Karp. But as the pattern is the word
"test" which is only 4 bytes long,
a brute force search is used, using SSE type instructions where available.
So the naive Go approach will give you a very fast execution. The main
thing is to set up your scanner with a large buffer, to minimize the number
of file system reads, and to avoid the newbie error of working with strings
rather than []byte, and forcing the code to do vast numbers of
unnecessary and expensive allocations.
On Saturday, 7 May 2022 at 22:53:54 UTC+1 Amnon wrote:
> p.s. If you changed the above code to use strings rather than []byte
> it would run many times slower due to the cost of allocation.
>
> On Saturday, 7 May 2022 at 22:49:08 UTC+1 Amnon wrote:
>
>> How about something like
>>
>> func grep(pat []byte, r io.Reader, w io.Writer) error {
>> scanner := bufio.NewScanner(r)
>> for scanner.Scan() {
>> if (bytes.Contains(scanner.Bytes(), pat)) {
>> w.Write(scanner.Bytes())
>> }
>> }
>>
>> return scanner.Err()
>> }
>>
>> and for extra speed, just allocate a bigger buffer to the scanner...
>> On Saturday, 7 May 2022 at 21:46:33 UTC+1 Jan Mercl wrote:
>>
>>> On Sat, May 7, 2022 at 10:24 PM Constantine Vassilev <ths...@gmail.com>
>>> wrote:
>>>
>>> > I need to write a program that reads STDIN and should output every
>>> line that contains a search word "test" to STDOUT.
>>>
>>> Piping the data through grep(1) would be my first option.
>>>
>>
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