Introduction#

I wanted to automate GitHub Copilot CLI calls from Python using subprocess, but it kept failing unexpectedly.

After some investigation, I found that this isn’t a Copilot CLI-specific issue—it’s a common pitfall when automating CLI tools on Windows + PowerShell. Here’s what I learned.

What Happened#

When trying to call Copilot CLI with subprocess.run(), I encountered several issues:

• Quoting/escaping breaks (especially with ", newlines, or special characters in prompts)
• Command becomes too long (long prompts or paths can trigger WinError 206)
• CLI hangs waiting for interactive input

Important: You Need --add-dir for File Editing#

If you want Copilot to edit or output files, you must explicitly specify the target directories. Otherwise, Copilot won’t have access to read or write files, and the operation will fail.

--add-dir "<prompt_dir>"
--add-dir "<out_dir>"

Solution 1: Call via PowerShell#

Wrapping the command with PowerShell’s -Command tends to work better. This approach worked for me.

cmd_str = f'powershell.exe -Command "copilot -p \\\"{escaped_prompt}\\\" --model {model} --allow-all-tools --add-dir \\\"{prompt_dir}\\\" --add-dir \\\"{out_dir}\\\""'

Solution 2 (Recommended): Pass Prompt as Arguments#

To avoid quoting issues with long commands, pass the prompt via PowerShell’s param mechanism instead of embedding it directly in -Command.

import subprocess

ps = r'param($p,$m,$pd,$od) copilot -p $p --model $m --allow-all-tools --add-dir $pd --add-dir $od'

subprocess.run(
    ["powershell.exe", "-NoProfile", "-NonInteractive", "-Command", ps,
     "--", prompt, model, prompt_dir, out_dir],
    text=True,
    capture_output=True,
)

Summary#

• If your prompt contains " or newlines, avoid string embedding (use the param approach)
• For file editing/output, always include --add-dir
• Add -NoProfile/-NonInteractive for stable execution