shelljs/src/tail.js

var common = require('./common');
var fs = require('fs');

common.register('tail', _tail, {
  canReceivePipe: true,
  cmdOptions: {
    'n': 'numLines',
  },
});

//@
//@ ### tail([{'-n': \<num\>},] file [, file ...])
//@ ### tail([{'-n': \<num\>},] file_array)
//@ Available options:
//@
//@ + `-n <num>`: Show the last `<num>` lines of the files
//@
//@ Examples:
//@
//@ ```javascript
//@ var str = tail({'-n': 1}, 'file*.txt');
//@ var str = tail('file1', 'file2');
//@ var str = tail(['file1', 'file2']); // same as above
//@ ```
//@
//@ Read the end of a file.
function _tail(options, files) {
  var tail = [];
  var pipe = common.readFromPipe();

  if (!files && !pipe) common.error('no paths given');

  var idx = 1;
  if (options.numLines === true) {
    idx = 2;
    options.numLines = Number(arguments[1]);
  } else if (options.numLines === false) {
    options.numLines = 10;
  }
  options.numLines = -1 * Math.abs(options.numLines);
  files = [].slice.call(arguments, idx);

  if (pipe) {
    files.unshift('-');
  }

  var shouldAppendNewline = false;
  files.forEach(function (file) {
    if (file !== '-') {
      if (!fs.existsSync(file)) {
        common.error('no such file or directory: ' + file, { continue: true });
        return;
      } else if (common.statFollowLinks(file).isDirectory()) {
        common.error("error reading '" + file + "': Is a directory", {
          continue: true,
        });
        return;
      }
    }

    var contents = file === '-' ? pipe : fs.readFileSync(file, 'utf8');

    var lines = contents.split('\n');
    if (lines[lines.length - 1] === '') {
      lines.pop();
      shouldAppendNewline = true;
    } else {
      shouldAppendNewline = false;
    }

    tail = tail.concat(lines.slice(options.numLines));
  });

  if (shouldAppendNewline) {
    tail.push(''); // to add a trailing newline once we join
  }
  return tail.join('\n');
}
module.exports = _tail;