Question: When I use `svn diff` or `git diff` it shows lines like:

```
@@ -1,5 +1,9 @@

```

What do they mean?

Answer: 
Those are called (c)hunk headers and contain the range information.

They are surrounded by double at signs `@@`. They are of the format:

```
@@ -l,s +l,s @@

```

where `l` is the starting line number and `s` is the number of lines the change (c)hunk applies to for each respective file. The `-` indicates the original file and the `+` indicates the new (modified) file. Note that it not only shows affected lines, but also context lines.

The `-1,5` is in the original file (indicated by the `-`). It shows that that first line is the start and 5 affected / context lines

The `+1,9` is in the new (modified) file (indicated by the `+`) and again first line is the start and 9 affected / context lines.

More details here: <http://en.wikipedia.org/wiki/Diff#Unified_format>
**Simple example analysis**

The format is basically the same the `diff -u` unified diff.

For instance:

```
diff -u <(seq 16) <(seq 16 | grep -Ev '^(2|3|14|15)$')

```

Here we removed lines 2, 3, 14 and 15. Output:

```
@@ -1,6 +1,4 @@
 1
-2
-3
 4
 5
 6
@@ -11,6 +9,4 @@
 11
 12
 13
-14
-15
 16

```

`@@ -1,6 +1,4 @@` means:

* `-1,6` means that this piece of the first file starts at line 1 and shows a total of 6 lines. Therefore it shows lines 1 to 6.

```
1
2
3
4
5
6

```

`-` means "old", as we usually invoke it as `diff -u old new`.
* `+1,4` means that this piece of the second file starts at line 1 and shows a total of 4 lines. Therefore it shows lines 1 to 4.

`+` means "new".

We only have 4 lines instead of 6 because 2 lines were removed! The new hunk is just:

```
1
4
5
6

```

`@@ -11,6 +9,4 @@` for the second hunk is analogous:

* on the old file, we have 6 lines, starting at line 11 of the old file:

```
11
12
13
14
15
16

```
* on the new file, we have 4 lines, starting at line 9 of the new file:

```
11
12
13
16

```

Note that line `11` is the 9th line of the new file because we have already removed 2 lines on the previous hunk: 2 and 3.

**Hunk header**

Depending on your git version and configuration, you can also get a code line next to the `@@` line, e.g. the `func1() {` in:

```
@@ -4,7 +4,6 @@ func1() {

```

This can also be obtained with the `-p` flag of plain `diff`.

Example: old file:

```
func1() {
    1;
    2;
    3;
    4;
    5;
    6;
    7;
    8;
    9;
}

```

If we remove line `6`, the diff shows:

```
@@ -4,7 +4,6 @@ func1() {
     3;
     4;
     5;
-    6;
     7;
     8;
     9;

```

Note that this is not the correct line for `func1`: it skipped lines `1` and `2`.

This awesome feature often tells exactly to which function or class each hunk belongs, which is very useful to interpret the diff.

How the algorithm to choose the header works exactly is discussed at: [Where does the excerpt in the git diff hunk header come from?](https://stackoverflow.com/questions/28111035/where-does-the-excerpt-in-the-git-diff-hunk-header-come-from)