Merge branch 'sr/log-SG-no-textconv'
[git/git.git] / Documentation / technical / api-builtin.txt
1 builtin API
2 ===========
3
4 Adding a new built-in
5 ---------------------
6
7 There are 4 things to do to add a built-in command implementation to
8 Git:
9
10 . Define the implementation of the built-in command `foo` with
11 signature:
12
13 int cmd_foo(int argc, const char **argv, const char *prefix);
14
15 . Add the external declaration for the function to `builtin.h`.
16
17 . Add the command to `commands[]` table in `handle_internal_command()`,
18 defined in `git.c`. The entry should look like:
19
20 { "foo", cmd_foo, <options> },
21 +
22 where options is the bitwise-or of:
23
24 `RUN_SETUP`::
25
26 Make sure there is a Git directory to work on, and if there is a
27 work tree, chdir to the top of it if the command was invoked
28 in a subdirectory. If there is no work tree, no chdir() is
29 done.
30
31 `USE_PAGER`::
32
33 If the standard output is connected to a tty, spawn a pager and
34 feed our output to it.
35
36 `NEED_WORK_TREE`::
37
38 Make sure there is a work tree, i.e. the command cannot act
39 on bare repositories.
40 This only makes sense when `RUN_SETUP` is also set.
41
42 . Add `builtin-foo.o` to `BUILTIN_OBJS` in `Makefile`.
43
44 Additionally, if `foo` is a new command, there are 3 more things to do:
45
46 . Add tests to `t/` directory.
47
48 . Write documentation in `Documentation/git-foo.txt`.
49
50 . Add an entry for `git-foo` to `command-list.txt`.
51
52 . Add an entry for `/git-foo` to `.gitignore`.
53
54
55 How a built-in is called
56 ------------------------
57
58 The implementation `cmd_foo()` takes three parameters, `argc`, `argv,
59 and `prefix`. The first two are similar to what `main()` of a
60 standalone command would be called with.
61
62 When `RUN_SETUP` is specified in the `commands[]` table, and when you
63 were started from a subdirectory of the work tree, `cmd_foo()` is called
64 after chdir(2) to the top of the work tree, and `prefix` gets the path
65 to the subdirectory the command started from. This allows you to
66 convert a user-supplied pathname (typically relative to that directory)
67 to a pathname relative to the top of the work tree.
68
69 The return value from `cmd_foo()` becomes the exit status of the
70 command.