Like other projects, we also have some guidelines to keep to the

code. For git in general, three rough rules are:

- Most importantly, we never say "It's in POSIX; we'll happily

ignore your needs should your system not conform to it."

We live in the real world.

- However, we often say "Let's stay away from that construct,

it's not even in POSIX".

- In spite of the above two rules, we sometimes say "Although

this is not in POSIX, it (is so convenient | makes the code

much more readable | has other good characteristics) and

practically all the platforms we care about support it, so

let's use it".

Again, we live in the real world, and it is sometimes a

judgement call, the decision based more on real world

constraints people face than what the paper standard says.

As for more concrete guidelines, just imitate the existing code

(this is a good guideline, no matter which project you are

contributing to). But if you must have a list of rules,

here they are.

For shell scripts specifically (not exhaustive):

- We prefer $( ... ) for command substitution; unlike ``, it

properly nests. It should have been the way Bourne spelled

it from day one, but unfortunately isn't.

- We use ${parameter-word} and its [-=?+] siblings, and their

colon'ed "unset or null" form.

- We use ${parameter#word} and its [#%] siblings, and their

doubled "longest matching" form.

- We use Arithmetic Expansion $(( ... )).

- No "Substring Expansion" ${parameter:offset:length}.

- No shell arrays.

- No strlen ${#parameter}.

- No regexp ${parameter/pattern/string}.

- We do not use Process Substitution <(list) or >(list).

- We prefer "test" over "[ ... ]".

- We do not write the noiseword "function" in front of shell

functions.

For C programs:

- We use tabs to indent, and interpret tabs as taking up to

8 spaces.

- We try to keep to at most 80 characters per line.

- When declaring pointers, the star sides with the variable

name, i.e. "char *string", not "char* string" or

"char * string". This makes it easier to understand code

like "char *string, c;".

- We avoid using braces unnecessarily. I.e.

if (bla) {

x = 1;

}

is frowned upon. A gray area is when the statement extends

over a few lines, and/or you have a lengthy comment atop of

it. Also, like in the Linux kernel, if there is a long list

of "else if" statements, it can make sense to add braces to

single line blocks.

- Try to make your code understandable. You may put comments

in, but comments invariably tend to stale out when the code

they were describing changes. Often splitting a function

into two makes the intention of the code much clearer.

- Double negation is often harder to understand than no negation

at all.

- Some clever tricks, like using the !! operator with arithmetic

constructs, can be extremely confusing to others. Avoid them,

unless there is a compelling reason to use them.

- Use the API. No, really. We have a strbuf (variable length

string), several arrays with the ALLOC_GROW() macro, a

path_list for sorted string lists, a hash map (mapping struct

objects) named "struct decorate", amongst other things.

- When you come up with an API, document it.

- The first #include in C files, except in platform specific

compat/ implementations, should be git-compat-util.h or another

header file that includes it, such as cache.h or builtin.h.

- If you are planning a new command, consider writing it in shell

or perl first, so that changes in semantics can be easily

changed and discussed. Many git commands started out like

that, and a few are still scripts.

- Avoid introducing a new dependency into git. This means you

usually should stay away from scripting languages not already

used in the git core command set (unless your command is clearly

separate from it, such as an importer to convert random-scm-X

repositories to git).