[BUG] Bash tool generates invalid awk commands with backslash-escaped exclamation marks

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

Claude Code generates awk commands with incorrectly escaped exclamation marks (\!), causing awk syntax errors. The ! negation operator in awk does not need backslash escaping, and doing so produces backslash not last character on line errors.

What Should Happen?

The ! operator in awk should not be backslash-escaped. The correct command would use ! directly:

awk '/^diff --git a\/openapi-/,/^diff --git/ { if (/^diff --git/ && !/^diff --git a\/openapi-/) exit; print }'

Error Messages/Logs

⏺ Bash(gh pr diff 432 | awk '/^diff --git a\/backend\/internal\//,/^diff --git/ { if (/^diff --git/ && !/^diff --git a\/backend\/internal\//) { if (!printed_stop) { pr…)
  ⎿  Error: Sibling tool call errored

⏺ Bash(gh pr diff 432 | awk 'BEGIN{p=0} /^diff --git a\/web-management\/src\/(components|routes)\//{ p=1 } /^diff --git/ && !/^diff --git a\/web-management\/src\/(comp…)
  ⎿  Error: Sibling tool call errored

⏺ Bash(gh pr diff 432 | awk 'BEGIN{p=0} /^diff --git a\/web-public\/app\/((\[locale\]|components|actions|fighter))/{ p=1 } /^diff --git/ && !/^diff --git a\/web-public…)
  ⎿  Error: Sibling tool call errored


All sibling parallel tool calls also failed as a result.

Steps to Reproduce

1. Ask Claude Code to review (with /review command) a PR diff filtered by file paths (e.g., gh pr diff <number> piped through awk)
2. Claude generates parallel awk commands to filter different sections of the diff
3. The generated awk patterns use \! instead of ! for negation

Claude Model

Opus

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.39

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Other

Additional Information

I use Ghostty for terminal with zsh