Gemini Agent (wrapper)

Thin wrapper around gemini CLI for non-interactive use:

• Provide prompt via arguments, PROMPT_FILE, or stdin
• Model selection via --model or GEMINI_MODEL env var
• Session resume via --resume or GEMINI_SESSION env var
• Auto-detects OAuth creds (~/.gemini/oauth_creds.json) for authentication
• Clear error messages with auto-diagnostics on failure

Prerequisites

Gemini CLI v0.20.0+ required (for --resume support):

npm install -g @google/gemini-cli@latest
gemini --version  # should be 0.20.0 or higher

Authentication (one of these):

1. Run gemini interactively once to complete OAuth login (creates ~/.gemini/oauth_creds.json)
2. Set GEMINI_API_KEY environment variable
3. Set GOOGLE_GENAI_USE_GCA=true with existing OAuth creds

Which Input Method to Use?

Choose ONE method based on your situation:

Situation	Method	Example
Short inline prompt	Args	gemini-agent "Explain X"
Prompt already exists in a file	PROMPT_FILE	PROMPT_FILE=task.md gemini-agent
Building prompt dynamically	Heredoc	gemini-agent <<'EOF'<br>your prompt<br>EOF
Piping from another command	Stdin	cat file.md | gemini-agent

Key concept: PROMPT_FILE means "read this file's contents AS the prompt" - the entire file becomes your prompt.

Usage Examples

Args (short prompts)

gemini-agent "Explain how async/await works in JavaScript"
gemini-agent "Review this code for bugs: $(cat snippet.js)"

PROMPT_FILE (prompt is in a file)

# The contents of task.md become the prompt
PROMPT_FILE=task.md gemini-agent

# With model selection
PROMPT_FILE=analysis-request.md GEMINI_MODEL=gemini-2.0-flash gemini-agent

Heredoc (multi-line dynamic prompts)

gemini-agent <<'EOF'
Context: We're building a VS Code extension.

Question: What's the best way to handle webview state persistence?

Please provide:
1. Recommended approach
2. Code example
3. Common pitfalls
EOF

Stdin (piping)

# Pipe file contents
cat requirements.md | gemini-agent

# Pipe command output
git diff HEAD~3 | gemini-agent "Review these changes:"

Common Mistakes

Don't combine input methods - use exactly ONE:

# WRONG: PROMPT_FILE with heredoc
PROMPT_FILE=/dev/stdin gemini-agent <<'EOF'
prompt here
EOF

# CORRECT: Just use heredoc directly
gemini-agent <<'EOF'
prompt here
EOF

# WRONG: PROMPT_FILE pointing to stdin
PROMPT_FILE=/dev/stdin gemini-agent

# CORRECT: Use pipe or heredoc
cat myfile.txt | gemini-agent

# WRONG: Mixing PROMPT_FILE with piped input
echo "extra" | PROMPT_FILE=task.md gemini-agent
# (stdin is ignored, only PROMPT_FILE is used - you'll get a warning)

# CORRECT: Choose one source
PROMPT_FILE=task.md gemini-agent
# OR
cat task.md extra.txt | gemini-agent

Session Resume

Capture the [session_id: ...] from output to continue conversations:

# Resume most recent session
gemini-agent --resume latest "Follow-up question"

# Resume by UUID (from previous output)
gemini-agent --resume c9283e30-910e-442c-b567-48ac9e1fab03 "Continue"

# Resume by index (use `gemini --list-sessions` to see available)
gemini-agent --resume 3 "Continue from session 3"

# Via environment variable
GEMINI_SESSION=c9283e30-910e-442c-b567-48ac9e1fab03 gemini-agent "Follow-up"

Model Selection

# Via flag
gemini-agent --model gemini-2.0-flash "Your prompt"

# Via environment variable
GEMINI_MODEL=gemini-2.0-flash gemini-agent "Your prompt"

Environment Variables

Variable	Description
PROMPT_FILE	Path to file whose contents become the prompt
GEMINI_MODEL	Model to use (passed as --model)
GEMINI_SESSION	Session to resume (latest, UUID, or index number)
GEMINI_API_KEY	API key authentication
GOOGLE_GENAI_USE_GCA	Set to true for Gemini Code Assist auth

Output

Returns plain text response followed by the session ID:

<response text>

[session_id: <uuid>]

Capture the session ID to continue the conversation with --resume <uuid>.

Troubleshooting

Diagnostics are shown automatically on any failure, including:

• What input method was used
• Prompt length and preview
• Authentication status
• Gemini CLI version

You can also run diagnostics manually:

gemini-agent --version

Common Issues

1. No auth configured: Run gemini interactively once to set up OAuth, or set GEMINI_API_KEY
2. gemini not found: Install with npm install -g @google/gemini-cli
3. --resume not working: Requires gemini CLI v0.20.0+ (gemini --version to check)
4. Connection errors: Check network connectivity and auth token expiry
5. Empty prompt error: Make sure your file/stdin/args actually contain content

Notes

• Runs gemini -y -o json -p <prompt> in non-interactive YOLO mode with JSON output to capture session_id
• Sessions are project-specific (tied to working directory)
• UUID-based resume requires full UUIDs (e.g., c9283e30-910e-442c-b567-48ac9e1fab03), not partial UUIDs
• Use gemini --list-sessions to see available sessions for current project

Session File Locations

For reference, session files are stored at:

• Path: ~/.gemini/tmp/{project_hash}/chats/session-*.json
• {project_hash} is the SHA256 hash of the working directory path
• Use gemini --list-sessions to list available sessions without needing to navigate the file structure