judgement call, the decision based more on real world
constraints people face than what the paper standard says.
+ - Fixing style violations while working on a real change as a
+ preparatory clean-up step is good, but otherwise avoid useless code
+ churn for the sake of conforming to the style.
+
+ "Once it _is_ in the tree, it's not really worth the patch noise to
+ go and fix it up."
+ Cf. http://article.gmane.org/gmane.linux.kernel/943020
+
Make your code readable and sensible, and don't try to be clever.
As for more concrete guidelines, just imitate the existing code
- We use tabs for indentation.
- - Case arms are indented at the same depth as case and esac lines.
+ - Case arms are indented at the same depth as case and esac lines,
+ like this:
+
+ case "$variable" in
+ pattern1)
+ do this
+ ;;
+ pattern2)
+ do that
+ ;;
+ esac
- Redirection operators should be written with space before, but no
space after them. In other words, write 'echo test >"$file"'
redirection target in a variable (as shown above), our code does so
because some versions of bash issue a warning without the quotes.
+ (incorrect)
+ cat hello > world < universe
+ echo hello >$world
+
+ (correct)
+ cat hello >world <universe
+ echo hello >"$world"
+
- We prefer $( ... ) for command substitution; unlike ``, it
properly nests. It should have been the way Bourne spelled
it from day one, but unfortunately isn't.
"then" should be on the next line for if statements, and "do"
should be on the next line for "while" and "for".
+ (incorrect)
+ if test -f hello; then
+ do this
+ fi
+
+ (correct)
+ if test -f hello
+ then
+ do this
+ fi
+
- We prefer "test" over "[ ... ]".
- We do not write the noiseword "function" in front of shell
functions.
- - We prefer a space between the function name and the parentheses. The
- opening "{" should also be on the same line.
- E.g.: my_function () {
+ - We prefer a space between the function name and the parentheses,
+ and no space inside the parentheses. The opening "{" should also
+ be on the same line.
+
+ (incorrect)
+ my_function(){
+ ...
+
+ (correct)
+ my_function () {
+ ...
- As to use of grep, stick to a subset of BRE (namely, no \{m,n\},
[::], [==], or [..]) for portability.
interface translatable. See "Marking strings for translation" in
po/README.
+ - We do not write our "test" command with "-a" and "-o" and use "&&"
+ or "||" to concatenate multiple "test" commands instead, because
+ the use of "-a/-o" is often error-prone. E.g.
+
+ test -n "$x" -a "$a" = "$b"
+
+ is buggy and breaks when $x is "=", but
+
+ test -n "$x" && test "$a" = "$b"
+
+ does not have such a problem.
+
+
For C programs:
- We use tabs to indent, and interpret tabs as taking up to
"char * string". This makes it easier to understand code
like "char *string, c;".
+ - Use whitespace around operators and keywords, but not inside
+ parentheses and not around functions. So:
+
+ while (condition)
+ func(bar + 1);
+
+ and not:
+
+ while( condition )
+ func (bar+1);
+
- We avoid using braces unnecessarily. I.e.
if (bla) {
of "else if" statements, it can make sense to add braces to
single line blocks.
- - We try to avoid assignments inside if().
+ - We try to avoid assignments in the condition of an "if" statement.
- Try to make your code understandable. You may put comments
in, but comments invariably tend to stale out when the code
* multi-line comment.
*/
+ Note however that a comment that explains a translatable string to
+ translators uses a convention of starting with a magic token
+ "TRANSLATORS: " immediately after the opening delimiter, even when
+ it spans multiple lines. We do not add an asterisk at the beginning
+ of each line, either. E.g.
+
+ /* TRANSLATORS: here is a comment that explains the string
+ to be translated, that follows immediately after it */
+ _("Here is a translatable string explained by the above.");
+
- Double negation is often harder to understand than no negation
at all.
+ - There are two schools of thought when it comes to comparison,
+ especially inside a loop. Some people prefer to have the less stable
+ value on the left hand side and the more stable value on the right hand
+ side, e.g. if you have a loop that counts variable i down to the
+ lower bound,
+
+ while (i > lower_bound) {
+ do something;
+ i--;
+ }
+
+ Other people prefer to have the textual order of values match the
+ actual order of values in their comparison, so that they can
+ mentally draw a number line from left to right and place these
+ values in order, i.e.
+
+ while (lower_bound < i) {
+ do something;
+ i--;
+ }
+
+ Both are valid, and we use both. However, the more "stable" the
+ stable side becomes, the more we tend to prefer the former
+ (comparison with a constant, "i > 0", is an extreme example).
+ Just do not mix styles in the same part of the code and mimic
+ existing styles in the neighbourhood.
+
+ - There are two schools of thought when it comes to splitting a long
+ logical line into multiple lines. Some people push the second and
+ subsequent lines far enough to the right with tabs and align them:
+
+ if (the_beginning_of_a_very_long_expression_that_has_to ||
+ span_more_than_a_single_line_of ||
+ the_source_text) {
+ ...
+
+ while other people prefer to align the second and the subsequent
+ lines with the column immediately inside the opening parenthesis,
+ with tabs and spaces, following our "tabstop is always a multiple
+ of 8" convention:
+
+ if (the_beginning_of_a_very_long_expression_that_has_to ||
+ span_more_than_a_single_line_of ||
+ the_source_text) {
+ ...
+
+ Both are valid, and we use both. Again, just do not mix styles in
+ the same part of the code and mimic existing styles in the
+ neighbourhood.
+
+ - When splitting a long logical line, some people change line before
+ a binary operator, so that the result looks like a parse tree when
+ you turn your head 90-degrees counterclockwise:
+
+ if (the_beginning_of_a_very_long_expression_that_has_to
+ || span_more_than_a_single_line_of_the_source_text) {
+
+ while other people prefer to leave the operator at the end of the
+ line:
+
+ if (the_beginning_of_a_very_long_expression_that_has_to ||
+ span_more_than_a_single_line_of_the_source_text) {
+
+ Both are valid, but we tend to use the latter more, unless the
+ expression gets fairly complex, in which case the former tends to
+ be easier to read. Again, just do not mix styles in the same part
+ of the code and mimic existing styles in the neighbourhood.
+
+ - When splitting a long logical line, with everything else being
+ equal, it is preferable to split after the operator at higher
+ level in the parse tree. That is, this is more preferable:
+
+ if (a_very_long_variable * that_is_used_in +
+ a_very_long_expression) {
+ ...
+
+ than
+
+ if (a_very_long_variable *
+ that_is_used_in + a_very_long_expression) {
+ ...
+
- 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.
documentation for version 2.6 does not mention this prefix, it has
been supported since version 2.6.0.
+Error Messages
+
+ - Do not end error messages with a full stop.
+
+ - Do not capitalize ("unable to open %s", not "Unable to open %s")
+
+ - Say what the error is first ("cannot open %s", not "%s: cannot open")
+
+
Writing Documentation:
Most (if not all) of the documentation pages are written in the