How to read a Diff
If you haven’t worked with diffs before, this can be something quite new or different.
If we have two files, let’s say a grocery list, in two files. We’ll call them ‘a’ and ‘b’.
Input: Old$ cat old 🍎 🍐 🍊 🍋 🍒 🥑
Output: New$ cat new 🍎 🍐 🍊 🍋 🍍 🥑
We can see that they have some different entries. We’ve removed 🍒 because they’re awful, and replaced them with an 🍍
Diff lets us compare these files
$ diff old new
5c5
< 🍒
---
> 🍍
Here we see that 🍒 is only in a, and 🍍 is only in b. But otherwise the files are identical.
There are a couple different formats to diffs, one is the ‘unified diff’
$ diff -U2 old new
--- old 2022-02-16 14:06:19.697132568 +0100
+++ new 2022-02-16 14:06:36.340962616 +0100
@@ -3,4 +3,4 @@
🍊
🍋
-🍒
+🍍
🥑
This is basically what you see in the training materials which gives you a lot of context about the changes:
--- old
is the ‘old’ file in our view+++ new
is the ‘new’ file- @@ these lines tell us where the change occurs and how many lines are added or removed.
- Lines starting with a - are removed from our ‘new’ file
- Lines with a + have been added.
So when you go to apply these diffs to your files in the training:
- Ignore the header
- Remove lines starting with - from your file
- Add lines starting with + to your file
The other lines (🍊/🍋 and 🥑) above just provide “context”, they help you know where a change belongs in a file, but should not be edited when you’re making the above change. Given the above diff, you would find a line with a 🍒, and replace it with a 🍍
Added & Removed Lines
Removals are very easy to spot, we just have removed lines
--- old 2022-02-16 14:06:19.697132568 +0100
+++ new 2022-02-16 14:10:14.370722802 +0100
@@ -4,3 +4,2 @@
🍋
🍒
-🥑
And additions likewise are very easy, just add a new line, between the other lines in your file.
--- old 2022-02-16 14:06:19.697132568 +0100
+++ new 2022-02-16 14:11:11.422135393 +0100
@@ -1,3 +1,4 @@
🍎
+🍍
🍐
🍊
Completely new files
Completely new files look a bit different, there the “old” file is /dev/null
, the empty file in a Linux machine.
$ diff -U2 /dev/null old
--- /dev/null 2022-02-15 11:47:16.100000270 +0100
+++ old 2022-02-16 14:06:19.697132568 +0100
@@ -0,0 +1,6 @@
+🍎
+🍐
+🍊
+🍋
+🍒
+🥑
And removed files are similar, except with the new file being /dev/null
--- old 2022-02-16 14:06:19.697132568 +0100
+++ /dev/null 2022-02-15 11:47:16.100000270 +0100
@@ -1,6 +0,0 @@
-🍎
-🍐
-🍊
-🍋
-🍒
-🥑