node.js – 在NodeJS中读取第N行文件

var fs = require('fs');

function get_line(filename,callBACk) {
    var stream = fs.createReadStream(filename,{
      flags: 'r',encoding: 'utf-8',fd: null,mode: 0666,bufferSize: 64 * 1024
    });

    var fileData = '';
    stream.on('data',function(data){
      fileData += data;

      // The next lines should be improved
      var lines = fileData.split("\n");

      if(lines.length >= +line_no){
        stream.destroy();
        callBACk(null,lines[+line_no]);
      }
    });

    stream.on('error',function(){
      callBACk('Error',null);
    });

    stream.on('end',function(){
      callBACk('File end reached without finding line',null);
    });

}

get_line('./file.txt',1,function(err,linE){
  console.log('The line: ' + linE);
})

直接解决方案：

您应该使用slice方法而不是循环。

var fs = require('fs');

function get_line(filename,callBACk) {
    var data = fs.readFileSync(filename,'utf8');
    var lines = data.split("\n");

    if(+line_no > lines.length){
      throw new Error('File end reached without finding line');
    }

    callBACk(null,lines[+line_no]);
}

get_line('./file.txt',9,linE){
  console.log('The line: ' + linE);
})

for(var l in lines)不是循环遍历数组的最有效的方法，你应该这样做：

for(var i = 0,iMax = lines.length; i < iMax; i++){/* lines[i] */ }

异步方式：

var fs = require('fs');

function get_line(filename,callBACk) {
    fs.readFile(filename,function (err,data) {
      if (err) throw err;

      // Data is a buffer that we need to convert to a String
      // Improvement: loop over the buffer and stop when the line is reached
      var lines = data.toString('utf-8').split("\n");

      if(+line_no > lines.length){
        return callBACk('File end reached without finding line',null);
      }

      callBACk(null,lines[+line_no]);
    });
}

get_line('./file.txt',linE){
  console.log('The line: ' + linE);
})