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Julian Priest is making this patch on route to New Zealand from Canada via Denmark and California.

I've finished the patch now.

It's been a bit of an on the road project. As the patchwork and needle was obviously a security threat at the airport, I packed it in my luggage and then couldn't find it anywhere. Eventually it turned up in my kid's socks but I had to use thread from the motel sewing kit where I was staying for the stitching. As a result the embroidery is a bit thin but readable I hope.

I also forgot the back stitch instructions so the beginning is a bit more of a hack stitch.

I finally managed to finish the patch in the Gettty Center in LA. A guard came over and watched me making it but didn't comment. I felt intimidated so finished it off in the family activity centre where I blended right in.

Hope it get's back to you in time for the stitch up..

.. Yay! Looks like it arrived.

http://www.fedex.com/Tracking

Here's a photo of Julian's patch in the back of a 3D card of the Getty Museum, LA.

The patch contains a slogan:

“Make a diff”

This refers to the Unix and Gnu/Linux command diff.

Diff is a program that compares files line by line and is commonly used by programmers to find the lines that differ between versions of the same file.

# diff file1 file2

Here's an example using 2 excerpts of Mark Twain's autobiography contained in 2 files twain1.txt and twain2.txt

julian@laprador: cat twain1.txt

...all through my life my facts have had a substratum of truth, and
therefore they were not without value. Any person who is familiar with
me knows how to strike my average, and therfore knows how to get at
the jewel of any fact of mine and dig it out of its blue-clay
matrix. My mother knew that art. When I was seven or eight ...a
neighbor said to her, "Do you ever believe anything that that boy
says?" My mother said, "He is a well spring of truth, but you can't
bring up the whole well with one bucket. I know his average, therefore
he never deceives me. I discount him thirty per cent for embroidery,
and what is left is perfect and priceless truth, without a flaw in it
anywhere."

- Mark Twain's Autobiography

julian@laprador: cat twain2.txt

...all through my life my facts have had a substratum of truth, and
therefore they were not without value. Any person who is familiar with
me knows how to strike my average, and therfore knows how to get at
the jewel of any fact of mine and dig it out of its blue-clay
matrix. My mother knew that art. When I was seven or eight ...a
neighbor said to her, "Do you ever believe anything that that boy
says?" My mother said, "He is a well spring of truth, but you can't
bring up the whole well with one bucket. I know his average, therefore
he never deceives me. I discount him ninety per cent for embroidery,
and what is left is perfect and priceless truth, without a flaw in it
anywhere."

- Mark Twain's Autobiography

Using the diff command (with the -u flag which adds some context)

julian@laprador: diff -u twain2.txt twain1.txt

--- twain2.txt  2007-09-09 20:19:34.000000000 -0600
+++ twain1.txt  2007-09-09 23:35:24.000000000 -0600
@@ -6,7 +6,7 @@
 neighbor said to her, "Do you ever believe anything that that boy
 says?" My mother said, "He is a well spring of truth, but you can't
 bring up the whole well with one bucket. I know his average, therefore
-he never deceives me. I discount him ninety per cent for embroidery,
+he never deceives me. I discount him thirty per cent for embroidery,
 and what is left is perfect and priceless truth, without a flaw in it
 anywhere."

This snippet shows the differences between the files with a + and a - at the beginning of the contested lines as well as a bit of context around the difference.

We can save this snippet out to a file thusly

julian@laprador: diff -u twain2.txt twain1.txt > twain-patch.diff

The resulting file 'twain-patch.diff' in software development circles is called a patch.

The patch file can be used to amend the file.

In this case twain2.txt contains an embroidery of the truth not in the original quote, Marks mother gives him a 30 % discount on the truth rather than 90%.

Using the faulty file twain2.txt and the patch twain-patch.diff we can get back to the original quote by using another command patch.

julian@laprador: patch -u twain2.txt twain-patch.diff 

In open source development a contributor will often make a change to some publicly available code, perhaps to fix a bug that they have discovered. They will then make a patch file using diff which contains the code change and submit it to the code maintainer. The maintainer can then evaluate the fix by applying it to the source code. If they approve of the patch, it can be incorporated into the publicly maintained code repository.

This is a core process in open source development and this mechanism is one of the techniques used to allow many authors to contribute in smaller or larger ways to the enormous patchwork that is free and open source software.

Why not give it a go? Just download some code or even a text, make a change and a patch and submit it back into the public domain.

Go on make a diff!

• wikipedia diff entry
• wikipedia patch entry
• Gnu comparing and merging files
• diff man page
• patch man page

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