Shell style

Follow the Google Shell Style Guide
unless this document or repository tooling says otherwise.

Tooling

• Use Bash for repository scripts. Executable scripts start with
  #!/usr/bin/env bash, followed by the repository licence header.
• Use set -euo pipefail, quote expansions unless splitting is intentional,
  and make function variables local.
• Format with shfmt -bn -ci -i=2 -w and lint with shellcheck. Explain any
  necessary local suppression at the suppressed line.

Functions and effects

• Return computed values on standard output and capture them; do not mutate a
  caller variable with eval, printf -v, or a global variable.
• Send diagnostics to standard error.
• A function whose purpose is an external effect may perform that named effect,
  but changes to directories, shell options, and traps stay local.

Tests and temporary files

• Shell behavior requires a committed test just like C++ behavior.
• Prefer the existing C++ end-to-end harness when testing Carve itself. Adopt
  mboworks_bashtest only when the behavior is genuinely shell-specific.
• Put test files under the test-owned temporary directory. Do not add cleanup
  traps or broad recursive deletion for Bazel-managed scratch space.

Portability

• Target the Bash available on supported Linux and macOS CI runners.
• Resolve Bazel runfiles through TEST_SRCDIR and TEST_WORKSPACE.
• Prefer [[ ... ]], arithmetic (( ... )), and arrays over legacy tests and
  stringly argument assembly.
• Use lower-case names for local variables and functions. Preserve environment
  and runfile variable names.