Add AST_GREP_PATH environment variable for custom ast-grep command paths

[Copilot]

Users installing ast-grep via package managers (e.g., uv add ast-grep-cli) cannot use the MCP server since ast-grep isn't in PATH and must be invoked via wrapper commands like uv run ast-grep.

Changes

Core implementation:

• Added AST_GREP_PATH environment variable to configure the ast-grep command
• Enhanced run_command() to split space-separated commands into proper argument lists
• Defaults to ast-grep when unset for backward compatibility

Documentation:

• Added configuration examples in README for common use cases (uv, custom paths, npx)
• Updated CLI help text to document the environment variable

Tests:

• Added unit tests covering custom command paths with and without config files

Usage

Configure MCP clients to use ast-grep via uv:

{
  "mcpServers": {
    "ast-grep": {
      "command": "uv",
      "args": ["--directory", "/path/to/ast-grep-mcp", "run", "main.py"],
      "env": {
        "AST_GREP_PATH": "uv run ast-grep"
      }
    }
  }
}

Other examples:

• AST_GREP_PATH="/custom/path/to/ast-grep" for custom installations
• AST_GREP_PATH="npx ast-grep" for npm-based workflows

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• astral.sh
  • Triggering command: /usr/bin/curl curl -LsSf REDACTED (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

Original prompt

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This section details on the original issue you should resolve

<issue_title>Make ast-grep path configurable</issue_title>
<issue_description>Feature request

I installed ast-grep inside my python/uv project using uv add ast-grep-cli.

So ast-grep is not really in my PATH, but it could be started with uv run ast-grep.

Currently ast-grep-mcp merely assumes the ast-grep command can be found in PATH, and there is no way to tell it to execute uv run ast-grep instead.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Make ast-grep path configurable #25

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