Shell Scripting Practices

Shell Scripting Practices

Application skill for shell learning (from the archived awesome-guidelines style capsules). Load learning note for why; capsules for probes.

Core Principle

Bash is for thin orchestration, quote aggressively, avoid subshell traps, check every mutation, and migrate before scripts become undebuggable programs.

When to Use / NOT

• Writing or reviewing .sh utilities, CI glue, or agent shell runners.
• Debugging word-splitting, empty-arg, or pipe-subshell bugs.

NOT when:

• Logic exceeds ~100 lines or needs structured data, use Python/Go/etc.
• PowerShell-only environment (see awesome-guidelines PowerShell guide separately).

Workflow

1. Scope, confirm shell is appropriate; bash shebang + set for strict modes if project uses them (shell-style-scope-and-safety.md).
2. Arguments, "$@" forwarding; arrays for flag lists; quote all expansions (shell-style-quoting-and-arrays.md).
3. Conditionals, [[/((/readarray; no pipe-to-while when parent needs state (shell-style-control-flow-subshells.md).
4. Structure, constants → functions → main "$@"; local + split declare/assign; STDERR err() (shell-style-structure-and-errors.md).
5. Verify, shellcheck exit 0; exercise empty args, spaces in paths, and failure paths.

Red Flags

• Unquoted $var or $@.
• eval, SUID bit, or string-built command lines.
• cmd | while read then read parent variable.
• local x="$(cmd)" followed by $? check.
• Script past 100 lines without migration plan.

Verification

• shellcheck -x script.sh (or project wrapper) exit 0.
• Manual: args with spaces, empty optional flags, failing command path.
• Capsule checklist on review.

References

• awesome-guidelines/references/shell-style-learning-note.md
• awesome-guidelines/references/shell-style-scope-and-safety.md
• awesome-guidelines/references/shell-style-quoting-and-arrays.md
• awesome-guidelines/references/shell-style-control-flow-subshells.md
• awesome-guidelines/references/shell-style-structure-and-errors.md