Not one to be completely happy with all existing features I found the diff tool in Sublime Text 2 to be… lacking. The built in diff tool allows you to select two files in the folder explorer, right click and choose Diff Files. This action will produce a unified diff output.

I, however, would like to have a way to use a graphical diff tool, because I’m way too lazy to read the unified diff. So I decided to write a plugin for Sublime. This plugin will allow me to map a key to run a command that will compare the current tab’s content with the contents of the tab to the right. Let’s walk through what that looks like. By the way, plugins are written in Python.

First let’s get the boilerplate stuff out of the way. We’ll need to import some stuff and create a class that extends a built in Sublime class that will allow us to create a plugin.

import sublime, sublime_pluginimport subprocessfrom subprocess
import Popen
from string import Template

class CompareCommand(sublime_plugin.TextCommand):

Now we need to define the run()method. The first argument is a reference to self, followed by the edit environment, and an argument called command, which will be an string containing the path to the diff tool to run, and placeholders for the left and right file names. More on that later when we map our new command to a key.

def run(self, edit, command):

The first task is to write two methods. The first will identify the current buffer, or tab, we are working on when our plugin executes. The second method will identify the buffer directly to the right. These files will make up the left and right files to send to a diff tool.This task is done by first getting the current view’s ID, then looping over all open views and finding the tab adjacent to our open one.

def __getCurrentBufferInfo(self):
		return {
			"id": self.view.buffer_id(),
			"fileName": self.view.file_name()
		}

	def __getNextBufferInfo(self, currentBuffer):
		result = None
		found = False

		for b in self.view.window().views():
			if found:
				result = {
					"id": b.buffer_id(),
					"fileName": b.file_name()
				}

				break

			if b.buffer_id() == currentBuffer["id"]:
				found = True

		return result

Once we have the two file names we are going to compare let’s open up the specified diff tool and pass the files in. Our command in the key mapping will define a string, and there will be two variables in there: $leftFileand $rightFile. To fill in the variables we will use the Templateclass. Once our string is filled in with file names we will use the Subprocessclass to execute. If there are any errors they will be output to the Sublime console. Here is the entire listing.

import sublime, sublime_plugin
import subprocess
from subprocess import Popen
from string import Template

class CompareCommand(sublime_plugin.TextCommand):
	def run(self, edit, command):
		currentBuffer = self.__getCurrentBufferInfo()
		nextBuffer = self.__getNextBufferInfo(currentBuffer)

		#
		# Compare the contents of the current buffer with the
		# contents of the next buffer (if there is one).
		#
		processCommand = []

		if nextBuffer != None:
			processCommand = Template(command).substitute(leftFile = currentBuffer["fileName"], rightFile = nextBuffer["fileName"])
			print processCommand

			#
			# Execute the command. Capture output on STDOUT, and write it out
			# to Sublime's console.
			#
			p = Popen(processCommand, shell = True, stdout = subprocess.PIPE, stderr = subprocess.STDOUT)
			for line in p.stdout.readlines():
				print line

			ret = p.wait()
			print "Return code: %s" % (ret)

	def __getCurrentBufferInfo(self):
		return {
			"id": self.view.buffer_id(),
			"fileName": self.view.file_name()
		}

	def __getNextBufferInfo(self, currentBuffer):
		result = None
		found = False

		for b in self.view.window().views():
			if found:
				result = {
					"id": b.buffer_id(),
					"fileName": b.file_name()
				}

				break

			if b.buffer_id() == currentBuffer["id"]:
				found = True

		return result

And now we can define a key mapping to be able to call our nifty plugin. Here is an example of a key mapping using the Meld diff tool in Ubuntu.

{ "keys": [ "ctrl+shift+c" ], "command": "compare", "args": { "command": "/usr/bin/meld '$leftFile' '$rightFile'" } }

If you take the code above and save it in the Packages/User directory as CompareCommand.py, and modify your user key mappings as shown above, you should be able to hit CTRL+SHIFT+C and compare two files.

Not perfect, but was fun to write, and will prove useful for me until the folks at Sublime put a full feature in and replace the need for this plugin. Happy coding!