Bug: Claude Code Installer Improperly Modifies ~/.zshrc Without Newline Separation

Bug Report: Claude Code Installer Improperly Modifies ~/.zshrc

Summary

Claude Code CLI auto-update process appends export PATH="$HOME/.local/bin:$PATH" to ~/.zshrc without a preceding newline, causing shell syntax errors.

Environment

• OS: macOS Darwin 24.6.0
• Shell: zsh
• Claude Code Version: 2.1.123 (auto-updated from 2.1.121/2.1.122)
• Date: April 29-30, 2026

Bug Description

During automatic updates (versions 2.1.121 → 2.1.122 → 2.1.123), the installer appended the PATH export line directly after the closing brace } of an existing function in ~/.zshrc without adding a newline separator.

Before (working):

  esac
}

After (broken):

  esac
}export PATH="$HOME/.local/bin:$PATH"

This created invalid shell syntax: }export on the same line, preventing ~/.zshrc from loading and causing "claude: command not found" errors.

Impact

• Complete shell startup failure
• Claude CLI inaccessible until manual fix
• Potential data loss risk if users don't understand the issue

Reproduction

• Have an existing ~/.zshrc with functions
• Allow Claude Code to auto-update
• Shell configuration gets corrupted

Expected Behavior

Installer should:

1. Check for existing content in shell config files
2. Add proper newline separation before appending
3. Validate shell syntax after modification

Actual Behavior

Installer blindly appends without newline separation, breaking shell syntax.

Suggested Fix

Add newline validation to installation scripts:

# Ensure file ends with newline before appending
if [ -s ~/.zshrc ] && [ "$(tail -c1 ~/.zshrc | wc -l)" -eq 0 ]; then
    echo "" >> ~/.zshrc
fi
echo 'export PATH="$HOME/.local/bin:$PATH"' >> ~/.zshrc

Additional Context

• This appears to be a common installer antipattern
• Similar issues reported with other CLI tools
• Binary signature verified as legitimate Anthropic release

Verification Details

• Binary Hash: 44597dff0f1c11e37c1954d4ac3965909be376e5961b558345723357253bcc90
• Code Signature: Valid, Team ID Q6L2SF6YDW
• Timestamp: Apr 29 02:57:58 2026