fix os detection on macOS with bash 3.2

[rickydtran]

macOS ships /bin/bash 3.2.57 which doesn't support ${os,,} (added in bash 4.0). When /usr/bin/env bash resolves to the system bash, is_macos() and is_linux() silently fail with bad substitution, so get_child_cmds never takes the macOS code path and SSH detection breaks — the split just opens a local shell.

Replace ${os,,} with tr '[:upper:]' '[:lower:]' <<< "$os" which works on all bash versions.

[coderabbitai]

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Reviewing files that changed from the base of the PR and between 5f1c852 and dacb8fd.

📒 Files selected for processing (1)

• scripts/tmux-ssh-split.sh

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📝 Walkthrough

Walkthrough

The pull request replaces Bash parameter expansion-based lowercasing with external tr command invocations in the is_linux and is_macos functions within the tmux SSH split script. The semantic behavior remains unchanged.

Changes

Cohort / File(s)	Summary
Lowercasing Method Refactor scripts/tmux-ssh-split.sh	Replaced bash parameter expansion (${var,,}) with tr command for lowercasing OS names in is_linux and is_macos functions. Functional behavior preserved.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~8 minutes

Poem

🐰 A rabbit hops through shell commands true,
From ${var,,} to tr anew,
The logic stays, just dressed in different clothes,
Where darwin and linux flow!

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the main change: replacing Bash-specific parameter expansion with shell-portable lowercasing to fix OS detection in zsh.

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[pschmitt]

My default shell is set to zsh too. I never encountered the issue you describe.
There's a bash shebang on top of the script.
How can i repro the issue?

[rickydtran]

My default shell is set to zsh too. I never encountered the issue you describe. There's a bash shebang on top of the script. How can i repro the issue?

I believe it's actually an old bash combat problem. I'm on macOS and had whatever it came shipped with bash 3.2.
I just installed a newer version bash 5.3 through brew without the changes and it worked. Looks like ${os,,} was added in bash 4.0.

Applied the <<< suggestion too, thanks. I'll update the PR and amend the commit