Shell shim

The shell shim is a universal integration that protects any AI tool that runs shell commands — with zero integration effort from the tool's side.

How it works

sl shield enable installs PATH-priority wrapper scripts in ~/.securitylayer/bin/. Because this directory is prepended to PATH, all shell commands route through Security Layer before reaching the real binary.

Shimmed binaries

Execution flow

AI Tool → shimmed bash → sl check → real bash
                              ↓ (if denied)
                         error message

1. AI tool calls bash -c "some command"
2. The shim in ~/.securitylayer/bin/bash intercepts
3. sl check evaluates the command
4. If allowed → forwarded to the real /usr/bin/bash
5. If denied → error returned, command never executes

Caller detection

The shim identifies which AI tool triggered the command by checking:

• Environment variables specific to each tool
• Parent process names

This allows different capability profiles for different tools (e.g., Claude Code gets exec + file.write, while an untrusted tool gets only file.read).

Setup

# Enable
sl shield enable

# Verify
sl shield status

# Disable
sl shield disable

After enabling, restart your shell or open a new terminal for the PATH change to take effect.

Supported AI tools

Any tool that executes shell commands is automatically protected:

• Claude Code
• Cursor
• Aider
• GitHub Copilot
• Custom agents
• Any tool running shell commands

See also

• shield — Shield command reference
• callers — Caller detection profiles
• check — The check command used by shims