var common = require('./common');
  var fs = require('fs');
  
  common.register('grep', _grep, {
    globStart: 2, // don't glob-expand the regex
    canReceivePipe: true,
    cmdOptions: {
      'v': 'inverse',
      'l': 'nameOnly',
    },
  });
  
  //@
  //@ ### grep([options,] regex_filter, file [, file ...])
  //@ ### grep([options,] regex_filter, file_array)
  //@ Available options:
  //@
  //@ + `-v`: Inverse the sense of the regex and print the lines not matching the criteria.
  //@ + `-l`: Print only filenames of matching files
  //@
  //@ Examples:
  //@
  //@ ```javascript
  //@ grep('-v', 'GLOBAL_VARIABLE', '*.js');
  //@ grep('GLOBAL_VARIABLE', '*.js');
  //@ ```
  //@
  //@ Reads input string from given files and returns a string containing all lines of the
  //@ file that match the given `regex_filter`.
  function _grep(options, regex, files) {
    // Check if this is coming from a pipe
    var pipe = common.readFromPipe();
  
    if (!files && !pipe) common.error('no paths given', 2);
  
    files = [].slice.call(arguments, 2);
  
    if (pipe) {
      files.unshift('-');
    }
  
    var grep = [];
    files.forEach(function (file) {
      if (!fs.existsSync(file) && file !== '-') {
        common.error('no such file or directory: ' + file, 2, { continue: true });
        return;
      }
  
      var contents = file === '-' ? pipe : fs.readFileSync(file, 'utf8');
      var lines = contents.split(/\r*
  /);
      if (options.nameOnly) {
        if (contents.match(regex)) {
          grep.push(file);
        }
      } else {
        lines.forEach(function (line) {
          var matched = line.match(regex);
          if ((options.inverse && !matched) || (!options.inverse && matched)) {
            grep.push(line);
          }
        });
      }
    });
  
    return grep.join('
  ') + '
  ';
  }
  module.exports = _grep;