[Buildroot] [External] RE: [PATCH 2/3] package/environment-setup: make script idempotent

[Arnout Vandecappelle]

On 07/01/2021 22:15, Schwarz, Konrad wrote:
> Hi Matt,
> 
>> -----Original Message-----
>> From: Matthew Weber <matthew.weber at collins.com>
>> Sent: Thursday, January 7, 2021 19:57
>> To: Schwarz, Konrad (T RDA IOT SES-DE) <konrad.schwarz at siemens.com>
>> Cc: buildroot <buildroot at buildroot.org>
>> Subject: Re: [External] RE: [Buildroot] [PATCH 2/3] package/environment-setup: make script idempotent
>>> As written, the code extends PATH only when the Buildroot-specific cross-compilation toolchain cannot be found (using a PATH
>> search).  Conversely: if the Buildroot-specific toolchain is already in PATH, PATH won't be extended.
>>>
>>> The only situation I see in which this might be undesirable is if an identically-prefixed toolchain that should not be used were already
>> in the PATH; the original code would simply override that (because it prefixes PATH).   I consider this a remote possibility, because the
>> "vendor" part of the GNU target triplet should be unique to Buildroot, at least when using the internal compilation toolchain option;
>> but fundamentally the same reasoning should apply to the external toolchain option (e.g., buildroot assumes the user knows what he
>> is doing in this case).
>>
>> Could you just grep the PATH to see if the SDK path is present instead of doing a command test?
> 
> 	command -v executable
> is _the_ POSIX compliant way of checking if an executable can be found via PATH.  See https://pubs.opengroup.org/onlinepubs/9699919799/utilities/command.html.  Trying to recreate this via grep or other means would seem to be clearly more error prone (and command -v, being a built-in, is faster to boot -- no pun intended). Additionally, environments such as MSYS, where the path separation character is not : (colon) but ; (semicolon), as in MS-DOS, additionally complicate a manual re-implementation of command -v.

 What Matt means is that, to avoid adding $SDK_PATH/bin to PATH when it is
already there, it is better to do

if ! echo "$PATH" | grep -q -E "(^|:)$SDK_PATH/bin($|:)"; then ...

 That way, you *exactly* check if it's a double entry or not.

 Regards,
 Arnout