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). It is always preferable to match the _local_ convention. New code added to git suite is expected to match the overall style of existing code. Modifications to existing code is expected to match the style the surrounding code already uses (even if it doesn't match the overall style of existing code). 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. - As to use of grep, stick to a subset of BRE (namely, no \{m,n\}, [::], [==], nor [..]) for portability. - We do not use \{m,n\}; - We do not use -E; - We do not use ? nor + (which are \{0,1\} and \{1,\} respectively in BRE) but that goes without saying as these are ERE elements not BRE (note that \? and \+ are not even part of BRE -- making them accessible from BRE is a GNU extension). 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. - We try to avoid assignments inside if(). - 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 string_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). - When we pass pair to functions, we should try to pass them in that order.