(#9400 P2a) Replace echo|tr/sed subshells with parameter expansion

[iav]

Summary

Replaces 6 instances where a for loop iterates over a comma-separated string by spawning echo … | tr/sed (or tr <<<) subshells. All replacements use bash-native parameter expansion ${VAR//,/ }, plus one switch from seq(1) to a C-style arithmetic loop and one switch from word-splitting $(< file) to mapfile. Part of the bash-safety cleanup tracked in #9400 (P2a).

GitHub issue reference: #9400
Jira reference number AR-2818

Changes

File	Before	After
lib/functions/general/extensions.sh	for x in $(echo "${ENABLE_EXTENSIONS:-${EXT}}" | tr "," " ")	local CSV var + ${_enable_csv//,/ }
lib/functions/configuration/interactive.sh	for x in $(echo "${KERNEL_TARGET}" | tr "," "\n")	for x in ${KERNEL_TARGET//,/ }
lib/functions/general/countdown.sh (×2)	for i in $(seq 1 "${loops}")	for ((i = 1; i <= loops; i++))
lib/functions/main/build-packages.sh	for x in $(tr ',' ' ' <<< "${CLEAN_LEVEL}")	for x in ${CLEAN_LEVEL//,/ }
lib/functions/rootfs/distro-agnostic.sh	for i in $(echo "${SERIALCON:-'ttyS0'}" | sed "s/,/ /g")	local CSV var + ${_serialcon_csv//,/ }; also drop the literal single quotes from the default (see follow-up commit below)
lib/functions/compilation/utils-compilation.sh (×2)	for dir in $(< /tmp/.overlayfs_wrapper_*)	mapfile -t arr < file; for dir in "${arr[@]}"

Why this matters

Each echo "${var}" | tr/sed form forks a subshell and one or two external processes just to do what bash can do in-place with ${var//pattern/replacement}. The replacements also reduce one class of word-splitting surprise: in the mapfile case, paths with whitespace are now preserved verbatim instead of being broken apart.

Note on intentional word splitting

The replacements for x in ${VAR//,/ } deliberately keep the expansion unquoted — that is the mechanism for the loop to split on whitespace. Inside [[ ]] or assignments these expansions would still need to be quoted; outside the loop header, they are not modified.

Follow-up: SERIALCON default

A separate commit drops the literal single quotes from the SERIALCON:-'ttyS0' default. When SERIALCON was unset, the value 'ttyS0' (with the quotes) was retained through the parameter expansion and downstream array[0] became the 4-character string 'ttyS0' — producing a malformed /etc/securetty entry and a non-existent serial-getty@'ttyS0'.service path.

Out of scope (deferred)

• bsp/armbian-bsp-cli-deb.sh:235 (from the original P2a list in Proposal: Improve Bash syntax safety across the codebase #9400): the relevant block has been refactored away since the audit was written; no change needed.

Summary by CodeRabbit

• Chores
  • Replaced subprocess-heavy list parsing with safer, faster in-shell split/iteration to reduce overhead.
  • Improved cleanup/unmount and extension-loading flows to iterate tracked entries reliably.
  • Simplified interactive configuration menus, countdown loops, cleaning fragments, and serial-console parsing for clearer parsing and maintainable behavior while preserving existing functionality.

[coderabbitai]

📝 Walkthrough

Walkthrough

Replace external shell pipelines and command-substitution loops with native Bash constructs: mapfile arrays for cleanup lists, arithmetic for-loops instead of seq, and parameter-expansion splitting for comma-separated values across several scripts.

Changes

Shell Syntax Modernization

Layer / File(s)	Summary
Overlay filesystem cleanup arrays lib/functions/compilation/utils-compilation.sh	Read overlay unmount and cleanup files into arrays via mapfile -t and iterate arrays for umount -l and removal.
Interactive kernel configuration lib/functions/configuration/interactive.sh	Split KERNEL_TARGET with ${KERNEL_TARGET//,/ } in interactive_config_ask_branch.
Countdown arithmetic loops lib/functions/general/countdown.sh	Replace for i in $(seq 1 ...) with for ((i = 1; i <= loops; i++)) in countdown functions.
Extension manager splitting and discovery lib/functions/general/extensions.sh	Split CSV extension lists with ${_enable_csv//,/ } for extension iteration.
Build package clean-level iteration lib/functions/main/build-packages.sh	Derive cleaning fragments from CLEAN_LEVEL using ${CLEAN_LEVEL//,/ } instead of tr.
Bootscript and console parameter handling lib/functions/rootfs/distro-agnostic.sh	Parse SERIALCON into a local _serialcon_csv (default ttyS0) and split via ${_serialcon_csv//,/ } when enabling serial getty instances.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Suggested reviewers

• hzyitc
• igorpecovnik

Poem

🐰 Pipelines trimmed, the shell leaps light,

Arrays collect what once took flight,
Loops count steadily, no subshell drum,
Commas expand, the tokens come,
A tidy warren, clean and bright.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 14.29% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The PR title accurately and specifically summarizes the main change: replacing echo|tr/sed subshells with bash parameter expansion across multiple files.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/p2a-for-loop-expansion

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@lib/functions/rootfs/distro-agnostic.sh`:
- Around line 509-510: The default value for SERIALCON currently includes
literal single quotes which become part of _serialcon_csv and break downstream
device names; change the assignment of local _serialcon_csv from
"${SERIALCON:-'ttyS0'}" to "${SERIALCON:-ttyS0}" (remove the single quotes) so
that when you split with ${_serialcon_csv//,/ } you get clean device names like
ttyS0 rather than 'ttyS0'; update the variable _serialcon_csv in the code where
it is declared to use the unquoted default.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro

Run ID: 74de7416-83c6-49c5-a198-749ae85d2345

📥 Commits

Reviewing files that changed from the base of the PR and between ebe3eeb and 6c9900c.

📒 Files selected for processing (6)

• lib/functions/compilation/utils-compilation.sh
• lib/functions/configuration/interactive.sh
• lib/functions/general/countdown.sh
• lib/functions/general/extensions.sh
• lib/functions/main/build-packages.sh
• lib/functions/rootfs/distro-agnostic.sh