On Unix like OSs, look for sqlpackage in directories specified in $PATH

[nick-gravgaard]

This PR addresses issue #2701 of sqlpackage not existing in the same place on MacOS and Linux distros by following the canonical Unix practice of searching the directories specified by the PATH environment variable instead of using a hard-coded path.

[mattgallagher92]

I've tested this out in my Ubuntu environment, where I have a symlink in /usr/local/bin to my sqlpackage install location, by running the expression Nick has added in F# interactive. It resolves correctly:

    Environment.pathDirectories
    |> Seq.map (fun dir -> !!(dir </> "sqlpackage"))
    |> Seq.concat
    |> Seq.map (fun path -> path, 15)

val it: seq<string * int> = seq [("/usr/local/bin/sqlpackage", 15)]

[yazeedobaid]

Thanks for the PR,
I would like to suggest keeping both ways. The old hard-coded way and the commonplace (best practice) as you mentioned. From what I see, now it will search in environment variables only. I'm thinking about a case when a user doesn't have SQL Package in the environment variables but is added to the directory that was hard-coded.

[yazeedobaid]

@mattgallagher92 thanks for testing and confirming the fix

[nick-gravgaard]

Thanks for the feedback @yazeedobaid. I was going to argue that it should be the user's responsibility to ensure their $PATH includes the directory sqlpackage is in, but if we don't do something like you suggest we risk breaking previously working setups. So I agree with you and have pushed up a new commit. First it checks $PATH, falling back to /usr/local/bin (where it currently lives on MacOS), and finally /usr/bin (where it currently lives on the Linux distros I know about).

I think this order is correct. The directories in $PATH should be checked first because that's where users can define their own locations for binaries. The next place should be /usr/local/bin because that's the location for normal user binaries not managed by the distro's package manager, eg. locally compiled packages. Finally we check /usr/bin because that's where distro-managed normal user binaries go.

Having /usr/local/bin before /usr/bin also matches the order in my $PATH as set by my distro, which reinforces my belief this is the most sensible order.