[英]node.js modify file data stream?
I need to copy one large data file to another destination with some modifications. 我需要将一个大型数据文件复制到另一个目的地并进行一些修改。
fs.readFile
and fs.writeFile
are very slow. fs.readFile
和fs.writeFile
非常慢。 I need to read line by line, modify and write to new file. 我需要逐行阅读,修改并写入新文件。 I found something like this:
我找到了这样的东西:
fs.stat(sourceFile, function(err, stat){
var filesize = stat.size;
var readStream = fs.createReadStream(sourceFile);
// HERE I want do some modifications with bytes
readStream.pipe(fs.createWriteStream(destFile));
})
But how to make modifications ? 但是如何进行修改? I tried to get data with
data
event 我试图用
data
事件获取数据
readStream.on('data', function(buffer){
var str = strToBytes(buffer);
str.replace('hello', '');
// How to write ???
});
but don't understand how to write it to file: 但不明白如何将其写入文件:
You should use transform
stream and use pipes like this: 您应该使用
transform
流并使用这样的管道:
fs.createReadStream('input/file.txt')
.pipe(new YourTransformStream())
.pipe(fs.createWriteStream('output/file.txt'))
Then it's just a matter of implementing the transform stream as in this doc 然后,这只是在本文档中实现转换流的问题
You can also make this easier for you using scramjet
like this: 你也可以使用
scramjet
这样更容易:
fs.createReadStream('input/file.txt')
.pipe(new StringStream('utf-8'))
.split('\n') // split every line
.map(async (line) => await makeYourChangesTo(line)) // update the lines
.join('\n') // join again
.pipe(fs.createWriteStream('output/file.txt'))
Which I suppose is easier than doing that manually. 我认为这比手动操作更容易。
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