读取NodeJS中文件的第N行
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考虑到我知道路径名和行号，我试图提取文件的一行，理想情况下，我希望这样做是在不读取多余文件的情况下进行的。
出于我在这里使用的目的，这是异步还是同步都没有关系。
我当前的（不良）实现如下所示：
function get_line(filename, line_no, callback) {
line_no = parseInt(line_no);
var data = fs.readFileSync(filename, \'utf8\');
var lines = data.split(\"\\n\");
for (var l in lines) {
if (l == line_no - 1) {
callback(null, lines[l].trim());
return;
}
}
throw new Error(\'File end reached without finding line\');
}
没有找到相关结果
已邀请:
3 个回复
田损比报
var fs = require(\'fs\'); function get_line(filename, line_no, 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); })var fs = require(\'fs\'); function get_line(filename, line_no, 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, function(err, line){ console.log(\'The line: \' + line); })for(var i = 0, iMax = lines.length; i < iMax; i++){/* lines[i] */ }var fs = require(\'fs\'); function get_line(filename, line_no, 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\', 9, function(err, line){ console.log(\'The line: \' + line); })挂帘妈乡
var n = 10; var l = null; //Internally it uses a buffer, default 16KB, but you can reduce it to, for example, 4KB doing: //new BufferedReader (\"file\", { encoding: \"utf8\", bufferSize: 4*1024 }) new BufferedReader (\"file\", { encoding: \"utf8\" }) .on (\"error\", function (error){ //error console.log (error); }) .on (\"line\", function (line){ if (!--n){ l = line; //With interrupt you can stop the reading this.interrupt (); } }) .on (\"end\", function (){ //your Nth line! console.log (l); }) .read ();琶竞捆栓
function(file, line_no, cb){ var stream = fs.createReadStream(file, { flags: \'r\', encoding: \'utf-8\', fd: null, mode: \'0666\', bufferSize: 64 * 1024 }); var fileData = \'\'; stream.on(\'data\', function(data){ fileData += data; var lines = fileData.split(\'\\n\'); if(lines.length >= +line_no){ stream.destroy(); cb(null, lines[+line_no]); } // Add this else condition to remove all unnecesary data from the variable else fileData = Array(lines.length).join(\'\\n\'); }); stream.on(\'error\', function(){ cb(\'Error\', null); }); stream.on(\'end\', function(){ cb(\'File end reached without finding line\', null); }); };