如何将此 Python 代码转换为 Node.js

关于如何在文件中清除一行/删除一行而不必截断文件或用新版本的文件替换文件，我在这里得到了一个很好的答案，这是 Python 代码:

I got a very nice answer on here about how to clear a line / delete a line in a file without having to truncate the file or replace the file with a new version of the file, here's the Python code:

#!/usr/bin/env python

import re,os,sys
logfile = sys.argv[1]
regex = sys.argv[2]

pattern = re.compile(regex)

with open(logfile,"r+") as f:
    while True:
        old_offset = f.tell()
        l = f.readline()
        if not l:
            break
        if pattern.search(l):
            # match: blank the line
            new_offset = f.tell()
            if old_offset > len(os.linesep):
                old_offset-=len(os.linesep)
            f.seek(old_offset)
            f.write(" "*(new_offset-old_offset-len(os.linesep)))

这个脚本可以这样调用:

this script can be called like:

./clear-line.py <file> <pattern>

出于教育目的，我想弄清楚我是否可以用 Node.js 编写它.我当然可以使用 Node.js 逐行读取文件.但我不确定 Node.js 在这种情况下是否有等效的 tell/seek 调用.

For educational purposes, I am trying to figure out if I can write this in Node.js. I can certainly read a file with Node.js line-by-line. But I am not sure if Node.js has the equivalent calls for tell/seek in this case.

写的等价物肯定是

https://nodejs.org/api/fs.html#fs_fs_write_fd_buffer_offset_length_position_callback

这是我的尝试

#!/usr/bin/env node

const readline = require('readline');
const fs = require('fs');

const file = process.argv[2];
const rgx = process.argv[3];

const fd = fs.openSync(file, 'r+');

const rl = readline.createInterface({
    input: fs.createReadStream(null, {fd: fd})
});

let position = 0;

const onLine = line => {

    position += line.length;

    if (String(line).match(rgx)) {

        let len = line.length;

        rl.close();
        rl.removeListener('line', onLine);

        // output the line that will be replaced/removed
        process.stdout.write(line);

        fs.write(fd, new Array(len + 1).join(' '), position, 'utf8', err => {
            if (err) {
                process.stderr.write(err.stack || err);
                process.exit(1);
            }
            else {
                process.exit(0);
            }

        });

    }

};

rl.on('line', onLine);

这不太正确 - 我认为我没有正确计算偏移/位置.也许同时了解 Python 和 Node 的人可以帮助我.我不太熟悉计算文件中的位置/偏移量，尤其是在缓冲区方面.

It's not quite right - I don't think I am calculating the offset/position correctly. Perhaps someone who know both Python and Node can help me out. I am not very familiar with calculating position/offset in files, especially in terms of buffers.

这是我正在使用的文本文件中的数据.我想要做的就是读取非空的第一行，然后从文件中删除该行并将该行写入标准输出.

Here is the data in a text file that I am working with. All I want to do is read the first line that is not empty, and then remove that line from the file and write that line to stdout.

这实际上可以是任何非空白数据，但这是我正在使用的 JSON:

This could really any non-whitespace data, but here is the JSON that I am working with:

{"dateCreated":"2016-12-26T09:52:03.250Z","pid":5371,"count":0,"uid":"7133d123-e6b8-4109-902b-7a90ade7c655","isRead":false,"line":"foo bar baz"}
{"dateCreated":"2016-12-26T09:52:03.290Z","pid":5371,"count":1,"uid":"e881b0a9-8c28-42bb-8a9d-8109587777d0","isRead":false,"line":"foo bar baz"}
{"dateCreated":"2016-12-26T09:52:03.390Z","pid":5371,"count":2,"uid":"065e51ff-14b8-4454-9ae5-b85152cfcb64","isRead":false,"line":"foo bar baz"}
{"dateCreated":"2016-12-26T09:52:03.491Z","pid":5371,"count":3,"uid":"5af80a95-ff9d-4252-9c4e-0e421fd9320f","isRead":false,"line":"foo bar baz"}
{"dateCreated":"2016-12-26T09:52:03.595Z","pid":5371,"count":4,"uid":"961e578f-288b-413c-b933-b791f833c037","isRead":false,"line":"foo bar baz"}
{"dateCreated":"2016-12-26T09:52:03.696Z","pid":5371,"count":5,"uid":"a65cbf78-2ea1-4c3a-9beb-b4bf56e83a6b","isRead":false,"line":"foo bar baz"}
{"dateCreated":"2016-12-26T09:52:03.799Z","pid":5371,"count":6,"uid":"d411e917-ad25-455f-9449-ae4d31c7b1ad","isRead":false,"line":"foo bar baz"}
{"dateCreated":"2016-12-26T09:52:03.898Z","pid":5371,"count":7,"uid":"46f8841d-c86c-43f2-b440-8ab7feea7527","isRead":false,"line":"foo bar baz"}
{"dateCreated":"2016-12-26T09:52:04.002Z","pid":5371,"count":8,"uid":"81b5ce7e-2f4d-4acb-884c-442c5ac4490f","isRead":false,"line":"foo bar baz"}
{"dateCreated":"2016-12-26T09:52:04.101Z","pid":5371,"count":9,"uid":"120ff45d-74e7-464e-abd5-94c41e3cd089","isRead":false,"line":"foo bar baz"}