[PATCH v3 1/5] CodingGuidelines: add shell piping guidelines

[Matthew DeVore <matvore@google.com>]

Add two guidelines:

 - pipe characters should appear at the end of lines, and not cause
   indentation
 - pipes should be avoided when they swallow exit codes that can
   potentially fail
---
 Documentation/CodingGuidelines | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/Documentation/CodingGuidelines b/Documentation/CodingGuidelines
index 48aa4edfb..6d265327c 100644
--- a/Documentation/CodingGuidelines
+++ b/Documentation/CodingGuidelines
@@ -118,6 +118,24 @@ For shell scripts specifically (not exhaustive):
 		do this
 	fi
 
+ - If a command sequence joined with && or || or | spans multiple
+   lines, put each command on a separate line and put && and || and |
+   operators at the end of each line, rather than the start. This
+   means you don't need to use \ to join lines, since the above
+   operators imply the sequence isn't finished.
+
+	(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 &&
+	...
+
  - We prefer "test" over "[ ... ]".
 
  - We do not write the noiseword "function" in front of shell
@@ -163,6 +181,15 @@ For shell scripts specifically (not exhaustive):
 
    does not have such a problem.
 
+ - In a piped chain such as "grep blob objects | sort", the exit codes
+   returned by processes besides the last are ignored. This means that
+   if git crashes at the beginning or middle of a chain, 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 $( ).
 
 For C programs:
 
-- 
2.19.0.444.g18242da7ef-goog