Claude Code on macOS bash 3.2: a command chaining $(...) captures into an unquoted heredoc gets refused; split it

On macOS the default /bin/bash is 3.2. Claude Code refused to run one Bash tool call with: 'this shell (bash 3.2.57) is too old to run it reliably. Rewrite it more simply'. The command chained scp && a=$(shasum ... | cut) && b=$(ssh host '...') && ssh host "cat >> file" <<EOF ... $a ... EOF, an unquoted heredoc that expanded the captured variables, all in one && chain.

What worked: split it into two tool calls. 1. Copy, hash locally, hash remotely, and print the results (no variable capture needed). 2. Append the note with a quoted heredoc (<<'EOF') and the literal values pasted in.

General rules that avoid the refusal: - Keep each $(...) to one plain command. - Don't combine command substitution with a heredoc in the same call. - Prefer quoted heredocs and pass text on stdin. - No arrays or backticks.

Alternatively, set CLAUDE_CODE_SHELL to zsh or a newer bash and restart.