[BUG] Bash tool corrupts commands with multi-line + pipe, and $() in pipes

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?

The Bash tool has two command parsing bugs that corrupt commands:

Bug 1: Multi-line + Pipe
When bash input contains both newlines and a pipe (anywhere), commands get corrupted. The echo keyword becomes literal text, or subsequent commands are passed as arguments to previous commands.

Bug 2: $() in Pipes
Command substitution $(...) gets mangled into \$ ( ... ) with spaces and escaping when the command contains a pipe, causing syntax errors.

What Should Happen?

Multi-line bash commands with pipes should execute correctly, with each line running as a separate command. Command substitution $() should work in piped commands without being mangled.

Error Messages/Logs

# Bug 1: Multi-line + Pipe (NO $ involved)

## Test A: Pipe on second line
Input:
  echo "a"
  echo "b" | cat

Expected: a then b (on separate lines)
Actual output: a echo b
(The "echo" keyword becomes literal text!)

## Test B: Pipe on first line
Input:
  echo "a" | cat
  echo "b"

Actual error:
  cat: echo: No such file or directory
  cat: b: No such file or directory
(Subsequent commands passed as filenames to cat!)

## Test C: Pipes on both lines
Input:
  echo "a" | cat
  echo "b" | cat

Actual error:
  cat: echo: No such file or directory

---

# Bug 2: $() Mangling in Pipes

## Test: echo $(whoami) | head -1
/usr/bin/bash: eval: line 1: syntax error near unexpected token `('
/usr/bin/bash: eval: line 1: `echo \$ ( whoami ) < /dev/null | head -1'

## Test: size=$(du -sh /tmp | cut -f1)
/usr/bin/bash: eval: line 1: syntax error near unexpected token `('
/usr/bin/bash: eval: line 1: `size=\$ ( du -sh /tmp < /dev/null | cut -f1 )'

Steps to Reproduce

Bug 1: Multi-line + Pipe

1. Start Claude Code
2. Ask Claude to run a multi-line bash command containing a pipe, e.g.:

``
echo "a"
echo "b" | cat
``

1. Observe corrupted output: a echo b instead of a then b

Bug 2: $() Mangling in Pipes

1. Start Claude Code
2. Ask Claude to run: echo $(whoami) | head -1
3. Observe syntax error revealing the mangled command:

echo \$ ( whoami ) < /dev/null | head -1

Controls that work:

• Single-line with pipe: echo "hello" | head -1 ✓
• Multi-line without pipe: multiple echo commands ✓
• $() without pipe: echo $(whoami) ✓

Claude Model

Opus

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.0.76 (Claude Code)

Platform

Anthropic API

Operating System

Ubuntu/Debian Linux

Terminal/Shell

Other

Additional Information

Terminal: Kitty (selected "Other" above)

Feedback ID: b2b45a09-6166-4572-bd59-c84425c414e6
(Also submitted via Claude Code's built-in /feedback command)

Note: This bug appears to be in the Bash tool's command parsing logic, specifically how it handles newlines and pipes. The error messages reveal an eval wrapper that mangles the commands.