Bug: non-portable use of #!/bin/bash shebang line breaks builds on FreeBSD/OpenBSD.

[yesudeep]

The binary for GNU Bash is located at different locations on different operating systems and is largely dependent on the package maintainers. For example:

• GNU/Linux distributions (generally): /bin/bash
• MacOS: /bin/bash
• FreeBSD: /usr/local/bin/bash
• OpenBSD: /usr/local/bin/bash

The use of #!/bin/bash in the shebang line for shell scripts is non-portable and may require a lot of selective patching for Bazel to build successfully on multiple operating systems if done on a case by case basis. Fortunately, there appears to be a portable workaround if one is acceptable. Please consider using:

#!/usr/bin/env bash instead of #!/bin/bash in the shebang line.

[yesudeep]

Noticed this problem when attempting to add a freebsd toolchain for rules_foreign_cc.

bazel-contrib/rules_foreign_cc#794

[tetromino]

The real fix for this would be Bazel support for the shell toolchain: bazelbuild/bazel#5265

[tetromino]

(By the way, please note that Bazel doesn't officially support FreeBSD or OpenBSD. We don't test on any BSD flavor other than macOS in the CI pipeline - which means that things might work on FreeBSD or OpenBSD, but there are no guarantees.)

[yesudeep]

Hi @tetromino understood. However, the PR I've sent should unblock a few things without affecting other platforms. Do you think it would be possible to take a look? Since I use Bazel on FreeBSD, I can continue to send patches whenever things break and if I find enough time can have a go at the better fix. wdyt?

[tetromino]

Seems reasonable, thanks. I've merged #329.