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---
name: command-composition-rules
description: The terminal has no shell: what is refused, what works, and how to verify a result that looks plausible
tags: [terminal, shell, composition, safety, agent]
category: system
---
## The rule
This terminal does not spawn a shell. The line is split into argv and handed to **one** command
handler. \`;\`, \`&&\`, \`||\` and redirection are not interpreted. Since v4.6.58 they are refused:
wc -l file && grep -c pattern file
-> warning: No shell here — \`&&\` is not interpreted. Run one command per line.
## Why the refusal exists
Before v4.6.58 \`&&\` failed silently: the right-hand tokens were appended to the left command's
argv, unknown tokens were dropped, and valid flags were absorbed.
wc -l f && grep -c x f -> "42 42" (grep's -c became a wc flag)
wc -l f && grep -n x f -> "42" (-n is not a wc flag, so it was dropped)
wc -c a b -> "34138 a" (second path dropped, exit code 0)
The worst case was an empty pattern: \`grep "" file\` matches every line and returns a plausible
count. A clean exit code is not evidence that the command did what you asked.
## What works
- One command per call. Two files means two calls, unless the command documents multiple paths.
- \`wc\` accepts multiple paths since v4.6.58: \`wc -c a b\` prints one line per file plus \`total\`.
- A single \`cmd | cmd\` pipeline works in the **interactive** terminal. It does **not** work through
the AI \`run_command\` tool, which bypasses the pipe splitter — there \`|\` is refused too.
- Operators inside quotes are untouched: \`echo "a && b"\` prints \`a && b\`.
## Verifying your own result
- Ask for two things, count that you got two lines back.
- A suspiciously round or empty count means a broken probe, not a clean system.
- \`ls\` prints text since v4.6.57 (it used to render chips only, so captured output was empty);
\`list_files\` remains the reliable enumerator.
- An invalid \`grep\` pattern now returns \`grep: invalid pattern: …\` and does not enter the error
ledger — if you see a pattern exception, something regressed.
## Pitfalls
- A refusal is not a failed command: nothing ran. Split it and run both halves.
- \`;\` used to fail loudly ("No such file: x;"). That loudness is gone in favour of an explicit
refusal — do not "fix" a refusal by re-joining the commands differently.
- \`>\` is handled by \`echo\` only (\`echo hi > file\`). It is not a general redirect.
## History
Replaces \`terminal-commands-silently-failing\` and \`command-composition-rules\`, merged 2026-10-23
after the behaviour itself was fixed in v4.6.58.
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