{"id":722,"date":"2013-12-13T08:18:51","date_gmt":"2013-12-13T16:18:51","guid":{"rendered":"http:\/\/galencharlton.com\/blog\/?p=722"},"modified":"2013-12-13T08:18:51","modified_gmt":"2013-12-13T16:18:51","slug":"koha-dev-tidbit-2-pinpoint-the-difference","status":"publish","type":"post","link":"https:\/\/galencharlton.com\/blog\/2013\/12\/koha-dev-tidbit-2-pinpoint-the-difference\/","title":{"rendered":"Koha Dev Tidbit #2: Pinpoint the difference"},"content":{"rendered":"

This morning I reviewed and pushed the patch for Koha bug 11174<\/a>. The patch, by Zeno Tajoli, removes one character each from two files.<\/p>\n

One character? That should be easy to eyeball, right?<\/p>\n

Not quite — the character in question was part of a parameter name in a very long URL. I don’t know about you, but it can take me a while to spot such a difference.<\/p>\n

Here is an example. Can you spot the exact difference in less than 2 seconds?<\/p>\n

\r\n$ git diff --color\r\n\r\ndiff --git a\/INSTALL b\/INSTALL\r\nindex ffe69ae..e92b1a3 100644\r\n--- a\/INSTALL\r\n+++ b\/INSTALL<\/strong>\r\n@@ -94,7 +94,7 @@<\/span> Use the packaged version or install from CPAN\r\n  sudo make upgrade\r\n \r\n Koha 3.4.x or later  no longer stores items in biblio records.\r\n-If you are upgrading from an older version ou will need to do the<\/span>\r\n+If you are upgrading from an older version you will need to do the<\/span>\r\n following two steps, they can take a long time (several hours) to\r\n complete for large databases\r\n<\/pre>\n
Now imagine doing this if the change occurs in the 100th character of a line that is 150 characters long.<\/p>\n
Fortunately, git diff<\/code>, as well as other commands like git show<\/code> that display diffs, accepts several switches that let you display the differences in terms of words, not lines.  These switches include --word-diff<\/code> and --color-words<\/code>.  For example:<\/p>\n
\r\n$ git diff --color-words\r\n\r\ndiff --git a\/INSTALL b\/INSTALL\r\nindex ffe69ae..e92b1a3 100644\r\n--- a\/INSTALL\r\n+++ b\/INSTALL<\/strong>\r\n@@ -94,7 +94,7 @@<\/span> Use the packaged version or install from CPAN\r\n  sudo make upgrade\r\n \r\nKoha 3.4.x or later  no longer stores items in biblio records.\r\nIf you are upgrading from an older version ou<\/span>you<\/span> will need to do the\r\nfollowing two steps, they can take a long time (several hours) to\r\ncomplete for large databases\r\n<\/pre>\n
\r\n$ git diff --word-diff\r\n\r\ndiff --git a\/INSTALL b\/INSTALL\r\nindex ffe69ae..e92b1a3 100644\r\n--- a\/INSTALL\r\n+++ b\/INSTALL\r\n@@ -94,7 +94,7 @@ Use the packaged version or install from CPAN\r\n sudo make upgrade\r\n\r\nKoha 3.4.x or later  no longer stores items in biblio records.\r\nIf you are upgrading from an older version [-ou-]{+you+} will need to do the\r\nfollowing two steps, they can take a long time (several hours) to\r\ncomplete for large databases\r\n<\/pre>\n
Going back to the bug I mentioned, --word-diff<\/code> wasn’t quite enough, though.  By default, Git considers words to be delimited by whitespace, but the patch in question removed a character from the middle of a very long URL.  To make the change pop out, I had to tell Git to highlight single-character changes.  One way to do this is the --word-diff-regex<\/code> or by passing the regex to --color-words.<\/code>  Here’s the final example:<\/p>\n
\r\n$ git diff --color-words=.\r\n\r\ndiff --git a\/INSTALL b\/INSTALL\r\nindex ffe69ae..e92b1a3 100644\r\n--- a\/INSTALL\r\n+++ b\/INSTALL<\/strong>\r\n@@ -94,7 +94,7 @@<\/span> Use the packaged version or install from CPAN\r\n  sudo make upgrade\r\n \r\nKoha 3.4.x or later  no longer stores items in biblio records.\r\nIf you are upgrading from an older version y<\/span>ou will need to do the\r\nfollowing two steps, they can take a long time (several hours) to\r\ncomplete for large databases\r\n<\/pre>\n
And there we have it — the difference, pinpointed.<\/p>\n
Share this:<\/h3>
The difference is much easier to see now — at least if you’re not red-green color-blind.  You can change the colors<\/a> or not use colors at all:<\/p>\n