codex-exec

Codex Exec

Run OpenAI's Codex CLI non-interactively to execute tasks. This is the headless workhorse of Codex — it takes a prompt, runs it, and returns the result without an interactive TUI.

Basic usage

codex exec "your prompt here" 2>/dev/null

Always append 2>/dev/null to suppress thinking tokens on stderr.

Prompt patterns

Inline prompt

codex exec "Refactor the User model to add email validation" 2>/dev/null

Piped prompt (for longer instructions or dynamic content)

echo "Review this function and suggest improvements:" | codex exec - 2>/dev/null

When stdin is piped and a prompt is also provided, stdin is appended as a <stdin> block:

cat some_file.py | codex exec "Review this code for security issues" 2>/dev/null

With images

codex exec -i screenshot.png "What UI issues do you see?" 2>/dev/null

Sandbox modes

Control what Codex can do on the filesystem:

Mode	Flag	Use case
Read-only	-s read-only	Safe analysis, review, questions
Workspace write	-s workspace-write	Code generation, file edits
Full access	-s danger-full-access	System-level tasks (use with caution)
Full auto	--full-auto	Shortcut for -s workspace-write with minimal approval prompts

Default to read-only or workspace-write unless the user explicitly needs more.

Structured output

Use --output-schema to get Codex to return JSON matching a schema:

codex exec "Analyze this codebase for security issues" \
  --output-schema schema.json \
  -o result.json \
  2>/dev/null

Use --json to get all events as JSONL stream (useful for programmatic parsing):

codex exec "List all TODO comments" --json 2>/dev/null

Use -o <file> to save just the last message to a file:

codex exec "Summarize the recent changes" -o summary.txt 2>/dev/null

Resuming sessions headlessly

Continue a previous Codex session without the TUI:

codex exec resume --last 2>/dev/null

Or with a follow-up prompt:

echo "Now apply the fix you suggested" | codex exec --skip-git-repo-check resume --last 2>/dev/null

Model selection

Override the default model:

codex exec -m o3 "your prompt" 2>/dev/null

Working directory

Run Codex in a specific directory:

codex exec -C /path/to/project "your prompt" 2>/dev/null

Common patterns for Claude

Get a second opinion on code you wrote

codex exec -s read-only "Review the changes in the last commit. Are there any bugs or edge cases missed?" 2>/dev/null

Delegate a subtask

codex exec --full-auto "Write unit tests for src/utils/parser.py and save them to tests/test_parser.py" 2>/dev/null

Cross-model validation

codex exec -s read-only "I believe this function has O(n log n) complexity. Verify my analysis: $(cat src/sort.py)" 2>/dev/null

Edge cases

• Timeout: codex exec can take 30-120+ seconds depending on the task. Use a 300s timeout for complex tasks.
• Large output: For tasks generating lots of output, use -o <file> to capture the last message rather than parsing stdout.
• No git repo: If running outside a git repo, add --skip-git-repo-check.
• Ephemeral: Add --ephemeral if you don't need the session persisted for later resume/fork.