如何同步在node.js中模拟unix head命令

Question

在node.js中寻找同步方法，就像linux头。

我知道在节点中进行同步工作通常是一个坏主意，但是我有一个有效的用例。需要读取文件的前几行。

Answer 1

// Returns the first few lines of the file.
// file: the file to read.
// lines: the number of lines to return.
// maxBuffer: the maximum number of bytes to read from 
//            the beginning of the file. We default to 
//            1k per line requested.
function head(file, lines, maxBuffer) {
  lines = lines || 10;
  maxBuffer = maxBuffer || lines * 1000;
  var stats = fs.statSync(file);
  var upToMax = Math.min(maxBuffer, stats.size);
  var fileDescriptor = fs.openSync(file, 'r');
  var buffer = Buffer.alloc(upToMax);
  fs.readSync(fileDescriptor, buffer, 0, upToMax, 0);
  var lineA = buffer.toString('utf8').split(/r?n/);
  lineA = lineA.slice(0, Math.min(lines, lineA.length));
  // might be nicer just to return the array and let the
  // caller do whatever with it.
  return lineA.join('n');
}