<p>I'm looking for a tool that will, in bulk, add a license header to some source files, some of which already have the header.  Is there a tool out there that will insert a header, if it is not already present?</p>

<p><em>Edit: I am intentionally not marking an answer to this question, since answers are basically all environment-specific and subjective</em> </p>

Python 2 solution, modify for your own need
Features:
handles UTF headers (important for most IDEs)
recursively updates all files in target directory passing given mask (modify the .endswith parameter for the filemask of your language (.c, .java, ..etc)
ability to overwrite previous copyright text (provide old copyright parameter to do this)
optionally omits directories given in the
```
excludedir
```
array
```
```
# updates the copyright information for all .cs files
# usage: call recursive_traversal, with the following parameters
# parent directory, old copyright text content, new copyright text content

import os

excludedir = ["..\\Lib"]

def update_source(filename, oldcopyright, copyright):
    utfstr = chr(0xef)+chr(0xbb)+chr(0xbf)
    fdata = file(filename,"r+").read()
    isUTF = False
    if (fdata.startswith(utfstr)):
        isUTF = True
        fdata = fdata[3:]
    if (oldcopyright != None):
        if (fdata.startswith(oldcopyright)):
            fdata = fdata[len(oldcopyright):]
    if not (fdata.startswith(copyright)):
        print "updating "+filename
        fdata = copyright + fdata
        if (isUTF):
            file(filename,"w").write(utfstr+fdata)
        else:
            file(filename,"w").write(fdata)

def recursive_traversal(dir,  oldcopyright, copyright):
    global excludedir
    fns = os.listdir(dir)
    print "listing "+dir
    for fn in fns:
        fullfn = os.path.join(dir,fn)
        if (fullfn in excludedir):
            continue
        if (os.path.isdir(fullfn)):
            recursive_traversal(fullfn, oldcopyright, copyright)
        else:
            if (fullfn.endswith(".cs")):
                update_source(fullfn, oldcopyright, copyright)
    
     
oldcright = file("oldcr.txt","r+").read()
cright = file("copyrightText.txt","r+").read()
recursive_traversal("..", oldcright, cright)
exit()
```
```