fix(log): don't error out if the log file doesn't exist

closes TryGhost#303

lib/commands/log.js

@@ -1,4 +1,5 @@
 'use strict';
+const fs = require('fs-extra');
 const path = require('path');
 const includes = require('lodash/includes');
 const lastLines = require('read-last-lines');
@@ -21,10 +22,6 @@ class LogCommand extends Command {
             return Promise.reject(new errors.SystemError(`Ghost instance '${argv.name}' does not exist`));
         }
 
-        // Change into the cwd of the running ghost instance so we can do things
-        // relative to that
-        process.chdir(instance.dir);
-
         if (instance.running) {
             instance.loadRunningEnvironment();
         }
@@ -42,9 +39,17 @@ class LogCommand extends Command {
             }));
         }
 
-        let logFileName = path.join(process.cwd(), 'content/logs', `${instance.config.get('url').replace(/[^\w]/gi, '_')}_${this.system.environment}.log`);
+        let logFileName = path.join(instance.dir, 'content/logs', `${instance.config.get('url').replace(/[^\w]/gi, '_')}_${this.system.environment}.log`);
         let prettyStream = new PrettyStream();
 
+        if (!fs.existsSync(logFileName)) {
+            if (argv.follow) {
+                this.ui.log('Log file has not been created yet, therefore the follow option won\'t work', 'yellow');
+            }
+
+            return Promise.resolve();
+        }
+
         prettyStream.on('error', (error) => {
             if (!(error instanceof SyntaxError)) {
                 throw error;