[PATCH v2 2/2] CodingGuidelines: Add note forbidding use of 'which' in shell scripts

From: Tim Henigan <tim.henigan@gmail.com>
Date: Feb 24, 2012, 23:12 UTC
Message-ID: <1330125178-9194-2-git-send-email-tim.henigan@gmail.com>
In-Reply-To: <1330125178-9194-1-git-send-email-tim.henigan@gmail.com>

During the code review of a recent patch, it was noted that shell scripts must not use 'which'. The output of the command is not machine parseable and its exit code is not reliable across platforms.

It is better to use 'type' to accomplish this task.

Signed-off-by: Tim Henigan <tim.henigan@gmail.com>
---

Updated to the documentation pattern recommended by Junio Hamano: "If you want to do Z, use X not Y, because Y is broken ..."

I grepped through the code and found the 'type <command' is indeed used in place of 'which' to test for the presence of commands on $PATH.

 Documentation/CodingGuidelines |    5 +++++
 1 files changed, 5 insertions(+), 0 deletions(-)

diff --git a/Documentation/CodingGuidelines b/Documentation/CodingGuidelines
index 5a190b9..816c5ad 100644
--- a/Documentation/CodingGuidelines
+++ b/Documentation/CodingGuidelines
@@ -49,6 +49,11 @@ For shell scripts specifically (not exhaustive):
    properly nests.  It should have been the way Bourne spelled
    it from day one, but unfortunately isn't.
 
+ - If you want to find out if a command is available on the user's
+   $PATH, you should use 'type <command>', instead of 'which'.
+   The output of 'which' is not machine parseable and its exit code
+   is not reliable across platforms.
+
  - We use POSIX compliant parameter substitutions and avoid bashisms;
    namely:

-- 
1.7.9.1