General utility to remove/strip all comments from source code in various languages?

Question

I am looking for a command-line tool that removes all comments from an input file and returns the stripped output. It'd be nice it supports popular programming languages like c, c++, python, php, javascript, html, css, etc. It has to be syntax-aware as opposed to regexp-based, since the latter will catch the pattern in source code strings as well. Is there any such tool?

I am fully aware that comments are useful information and often leaving them as they are is a good idea. It's just that my focus is on different use cases.

Answer 1

I don't know of such a tool - which isn't the same as saying there isn't one.

I once started to design one, but it quickly gets insane - not helped by the comment rules in C and C++.

/\
*  Comment? *\
/

(Answer: yes!)

"/\
* Comment? *\
/"

(Answer: no!)

To do the job reasonably, you have to be aware of:

• Language comment conventions
• Language quoted string conventions (Python and Perl are enough to drive you insane here)
• Escape conventions (Shell gets you here - along with the quotes)

These combine to make the job tolerably close to impossible.

I ended up with a program, scc, to strip C and C++ comments. Its torture test includes worse examples than the comments shown above - and it does a decent job. But extending that to do shell or Perl or Python or (take your pick) was sufficiently non-trivial that I did not do it.

Answer 2

cloc, a free Perl script, can do this.

Remove Comments from Source Code

How can you tell if cloc correctly identifies comments? One way to convince yourself cloc is doing the right thing is to use its --strip-comments option to remove comments and blank lines from files, then compare the stripped-down files to originals.

It supports a lot of languages.

Answer 3

You might coax GNU Source-highlight into doing this.

Answer 4

What you want can be done with emacs scripting.

I wrote this script for you which does exactly what you want and can be easily extended to any language.

Filename: kill-comments

#!/usr/bin/python                                                         

import subprocess                                                         
import sys                                                                
import os                                                                 

target_file = sys.argv[1]                                                 

command =   "emacs -batch -l ~/.emacs-batch " + \                         
    target_file + \                                                       
    " --eval '(kill-comment (count-lines (point-min) (point-max)))'" + \  
    " -f save-buffer"                                                     

#to load a custom .emacs script (for more syntax support),                
#use -l <file> in the above command                                       

#print command                                                            

fnull = open(os.devnull, 'w')                                             
subprocess.call(command, shell = True, stdout = fnull, stderr = fnull)    
fnull.close()

to use it just call:

kill-comments <file-name>

To add any language to it edit ~/.emacs-batch and add that language's major mode. You can find syntax aware modes for basically everything you could want at http://www.emacswiki.org.

As an example, here is my ~/.emacs-batch file. It extends the above script to remove comments from javascript files. (I have javascript.el in my ~/.el directory)

(setq load-path (append (list (concat (getenv "HOME") "/.el")) load-path))    
(load "javascript")                                               
(setq auto-mode-alist (cons '("\\.js$" . javascript-mode) auto-mode-alist))

With the javascript addition this will remove comments from all the filetypes you mentioned as well as many more.

Good Luck and happy coding!

Answer 5

Paul Dixon's response to this question on stripping comments from a script might be worth looking at.

Answer 6

No such tool exists yet.