Trade-off: #!/bin/bash or #!/usr/bin/env bash for a Repeatable Build Environment?
A shell-based build is being standardized so that the same source tree behaves identically on every developer machine and in CI. The build is driven by make, and several helper scripts require bash rather than a minimal POSIX shell, so the shebang line becomes part of the reproducibility contract. Two documented approaches exist. An absolute shebang such as
unix
bash