const fs = require('fs');
const readline = require('readline');

const file = readline.createInterface({
  input: fs.createReadStream('input.log'),
  output: process.stdout,
  terminal: false
});

file.on('line', (line) => {
  if (line.includes('warning')) {
    fs.appendFile('output.log', '\r\n\r\n', err => {
      if (err) {
        console.error(err);
      }
    });
  } else if (line.includes('error')) {
    console.log(line)
    fs.appendFile('output.log', line   "\r\n", err => {
      if (err) {
        console.error(err);
      }
    });
  }
});

The code works but I need to avoid putting the two newlines when "warning" is on the last line of the file

CodePudding user response：

You could try like this. This code won't save the last warning line at all:

const fs = require('fs');
const readline = require('readline');

const file = readline.createInterface({
  input: fs.createReadStream('input.log'),
  output: process.stdout,
  terminal: false,
});

let lastLine = '';
file.on('line', (line) => {
  if (lastLine) {
    fs.appendFile('output.log', lastLine, (err) => {
      if (err) {
        console.error(err);
      }
    });
  }

  if (line.includes('warning')) {
    console.log(line);
    lastLine = '\r\n\r\n';
  } else if (line.includes('error')) {
    console.log(line);
    lastLine = line   '\r\n';
  }
  else {
    lastLine = null;
  }
});

// only write last line if it was error
file.on('close', () => {
  if (!lastLine || lastLine === '\r\n\r\n') {
    return;
  }
  
  fs.appendFile('output.log', lastLine, (err) => {
    if (err) {
      console.error(err);
    }
  });
});