On Mon, Sep 17, 2018 at 5:16 PM Eric Sunshine <sunshine@xxxxxxxxxxxxxx> wrote:
>
> On Mon, Sep 17, 2018 at 6:24 PM Matthew DeVore <matvore@xxxxxxxxxx> wrote:
> > diff --git a/Documentation/CodingGuidelines b/Documentation/CodingGuidelines
> > @@ -163,6 +163,35 @@ For shell scripts specifically (not exhaustive):
> > + - In a piped sequence which spans multiple lines, put each statement
> > + on a separate line and put pipes on the end of each line, rather
> > + than the start. This means you don't need to use \ to join lines,
> > + since | implies a join already. Also, do not indent subsequent
> > + lines; if you need a sequence to visually stand apart from the
> > + surrounding code, use a blank line before and/or after the piped
> > + sequence.
> > +
> > + (incorrect)
> > + [...]
> > + (correct)
> > + echo '...' > expected
>
> Existing tests seem to favor the name "expect" over "expected", so
> perhaps use that instead.
>
> $ git grep '>expect\b' -- t | wc -l
> 2674
> $ git grep '>expected\b' -- t | wc -l
> 1406
Thank you for clarifying that out for me, but I'm not longer using
that example, so it's moot.
>
> > + git ls-files -s file.1 file.2 file.3 file.4 file.5 |
> > + awk '{print $1}' |
> > + sort >observed
>
> This is not a great example since it flatly contradicts the very next
> bit of advice added by this patch about not placing a Git command
> upstream in a pipe. Perhaps come up with an example which doesn't
> suffer this shortcoming.
Done.
>
> I've seen the advice earlier in the thread of not indenting the
> sub-commands in a pipe, but I find that the result makes it far more
> difficult to see which commands are part of the pipe sequence than
> with them indented, so I'm not convinced that this advice should be in
> the guidelines. (But that just my opinion.)
I'm not totally sure either way, nor do I have a strong opinion. I
agree it's probably better to not codify this in the documentation
until there's a great reason to.
>
> > + - In a pipe, any non-zero exit codes returned by processes besides
> > + the last will be ignored. If there is any possibility some
> > + non-final command in the pipe will raise an error, prefer writing
> > + the output of that command to a temporary file with '>' rather than
> > + pipe it.
>
> It's not so much that we care about losing a non-zero exit code (which
> might be perfectly acceptable depending upon the context) but that we
> care about missing a Git command which outright crashes. So, it might
> make sense to make this text more specific by saying that ("exit code
> indicating a crash" and "Git command") rather than being generic in
> saying only "exit code" and "command".
Fixed.
>
> Also, what about expression like $(git foo) by which a crash of a Git
> command can also be lost? Do we want to talk about that, as well?
Yes, it's probably better to add a point about that. Here is the new
documentation after applying your suggestions:
- If a piped sequence which spans multiple lines, put each statement
on a separate line and put pipes on the end of each line, rather
than the start. This means you don't need to use \ to join lines,
since | implies a join already.
(incorrect)
grep blob verify_pack_result \
| awk -f print_1.awk \
| sort >actual &&
...
(correct)
grep blob verify_pack_result |
awk -f print_1.awk |
sort >actual &&
...
- In a pipe, any exit codes returned by processes besides the last
are ignored. This means that if git crashes at the beginning or
middle of a pipe, it may go undetected. Prefer writing the output
of that command to a temporary file with '>' rather than pipe it.
- The $(git ...) construct also discards git's exit code, so if the
goal is to test that particular command, redirect its output to a
temporary file rather than wrap it with $( ).
