Node.js 将一行写入 .txt 文件
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Node.js Write a line into a .txt file
提问by Meterion
I want to create a simple Log System, which prints a line before the past line into a txt file by using Node.js, but i dont know how the File System from Node.js works. Can someone explain it ?
我想创建一个简单的日志系统，它使用 Node.js 将过去行之前的一行打印到 txt 文件中，但我不知道 Node.js 的文件系统是如何工作的。有人可以解释一下吗？
回答by Leonid Beschastny
Inserting data into the middle of a text file is not a simple task. If possible, you should append it to the end of your file.
将数据插入文本文件的中间并不是一项简单的任务。如果可能，您应该将其附加到文件的末尾。
The easiest way to append data some text file is to use build-in fs.appendFile(filename, data[, options], callback)functionfrom fsmodule:
追加数据的一些文本文件，最简单的方法是使用内置的fs.appendFile(filename, data[, options], callback)功能从fs模块：
var fs = require('fs')
fs.appendFile('log.txt', 'new data', function (err) {
if (err) {
// append failed
} else {
// done
}
})
But if you want to write data to log file several times, then it'll be best to use fs.createWriteStream(path[, options])functioninstead:
但是如果你想多次将数据写入日志文件，那么最好使用fs.createWriteStream(path[, options])函数：
var fs = require('fs')
var logger = fs.createWriteStream('log.txt', {
flags: 'a' // 'a' means appending (old data will be preserved)
})
logger.write('some data') // append string to your file
logger.write('more data') // again
logger.write('and more') // again
Node will keep appending new data to your file every time you'll call .write, until your application will be closed, or until you'll manually close the stream calling .end:
每次您调用 时.write，Node 都会将新数据附加到您的文件中，直到您的应用程序关闭，或者直到您手动关闭流调用.end：
logger.end() // close string
回答by michelem
Simply use fsmodule and something like this:
只需使用fs模块和类似的东西：
fs.appendFile('server.log', 'string to append', function (err) {
if (err) return console.log(err);
console.log('Appended!');
});
回答by Yene Mulatu
Step 1
第1步
If you have a small file Read all the file data in to memory
如果你有一个小文件 将所有文件数据读入内存
Step 2
第2步
Convert file data string into Array
将文件数据字符串转换为数组
Step 3
第 3 步
Search the array to find a location where you want to insert the text
搜索数组以找到要插入文本的位置
Step 4
第四步
Once you have the location insert your text
一旦你有位置插入你的文字
yourArray.splice(index,0,"new added test");
Step 5
第 5 步
convert your array to string
将您的数组转换为字符串
yourArray.join("");
Step 6
第 6 步
write your file like so
像这样写你的文件
fs.createWriteStream(yourArray);
This is not advised if your file is too big
如果您的文件太大，则不建议这样做
回答by ISURU THIWANKA
I did a log file which prints data into text file using "Winston" log. The source code is here below,
我做了一个日志文件，它使用“Winston”日志将数据打印到文本文件中。源代码在下面，
const { createLogger, format, transports } = require('winston');
var fs = require('fs')
var logger = fs.createWriteStream('Data Log.txt', {`
flags: 'a'
})
const os = require('os');
var sleep = require('system-sleep');
var endOfLine = require('os').EOL;
var t = ' ';var s = ' ';var q = ' ';
var array1=[];
var array2=[];
var array3=[];
var array4=[];
array1[0] = 78;`
array1[1] = 56;
array1[2] = 24;
array1[3] = 34;
for (var n=0;n<4;n++)
{
array2[n]=array1[n].toString();
}
for (var k=0;k<4;k++)
{
array3[k]=Buffer.from(' ');
}
for (var a=0;a<4;a++)
{
array4[a]=Buffer.from(array2[a]);
}
for (m=0;m<4;m++)
{
array4[m].copy(array3[m],0);
}
logger.write('Date'+q);
logger.write('Time'+(q+' '))
logger.write('Data 01'+t);
logger.write('Data 02'+t);
logger.write('Data 03'+t);
logger.write('Data 04'+t)
logger.write(endOfLine);
logger.write(endOfLine);
enter code here`enter code here`
}
function mydata() //user defined function
{
logger.write(datechar+s);
logger.write(timechar+s);
for ( n = 0; n < 4; n++)
{
logger.write(array3[n]);
}
logger.write(endOfLine);
}
for (;;)
}
var now = new Date();
var dateFormat = require('dateformat');
var date = dateFormat(now,"isoDate");
var time = dateFormat(now, "h:MM:ss TT ");
var datechar = date.toString();
var timechar = time.toString();
mydata();
sleep(5*1000);
}
