codex

Codex Subagent

Run OpenAI Codex CLI (GPT-5.2) for second opinions and external reviews.

Availability Check

Before using Codex, verify it's installed:

which codex >/dev/null 2>&1 || echo "CODEX_NOT_INSTALLED"

If not installed, inform the user: "Codex CLI is not installed. Skipping Codex review."

Execution Pattern

OUTPUT_FILE=$(mktemp)
codex exec \
  --skip-git-repo-check \
  --dangerously-bypass-approvals-and-sandbox \
  -o "$OUTPUT_FILE" \
  "$PROMPT" </dev/null 2>/tmp/codex_stderr.log
cat "$OUTPUT_FILE"
rm "$OUTPUT_FILE"

Flags

Flag	Purpose
exec	Non-interactive mode
--skip-git-repo-check	Run outside git repositories
--dangerously-bypass-approvals-and-sandbox	No prompts, no sandbox restrictions
-o <file>	Capture clean output to file
</dev/null	Required. Close stdin — without it codex blocks on "Reading additional input from stdin..." and the -o file comes back empty (exit 0, zero bytes). Bites hardest in non-interactive / background Bash where there's no TTY.
2>/tmp/codex_stderr.log	Send stderr to a file, not 2>/dev/null — if codex hangs or errors you need to see the stdin/auth message. Inspect the log when the output file is empty.

Timeout

Codex can take several minutes for complex prompts. Use 15 minute timeout:

timeout 900 codex exec --skip-git-repo-check --dangerously-bypass-approvals-and-sandbox -o "$OUTPUT_FILE" "$PROMPT" </dev/null 2>/tmp/codex_stderr.log

Usage Examples

Simple Question

OUTPUT_FILE=$(mktemp)
codex exec --skip-git-repo-check --dangerously-bypass-approvals-and-sandbox -o "$OUTPUT_FILE" \
  "What are the tradeoffs between Redis and Memcached for session storage?" 2>/dev/null
cat "$OUTPUT_FILE"
rm "$OUTPUT_FILE"

Code Review

DIFF=$(git diff main...HEAD)
OUTPUT_FILE=$(mktemp)
codex exec --skip-git-repo-check --dangerously-bypass-approvals-and-sandbox -o "$OUTPUT_FILE" \
  "Review this diff for issues:

$DIFF

List concerns with severity (blocking/important/nice-to-have)." 2>/dev/null
cat "$OUTPUT_FILE"
rm "$OUTPUT_FILE"

With Working Directory

OUTPUT_FILE=$(mktemp)
codex exec --dangerously-bypass-approvals-and-sandbox -C /path/to/repo -o "$OUTPUT_FILE" \
  "Analyze the architecture of this codebase" 2>/dev/null
cat "$OUTPUT_FILE"
rm "$OUTPUT_FILE"

GitHub PR Review

Codex has access to gh CLI. Pass the PR URL and let it fetch the diff:

OUTPUT_FILE=$(mktemp)
timeout 900 codex exec --skip-git-repo-check --dangerously-bypass-approvals-and-sandbox -o "$OUTPUT_FILE" \
  "Review this PR: https://github.com/owner/repo/pull/123

   Use gh CLI to get the diff and review for issues." 2>/dev/null
cat "$OUTPUT_FILE"
rm "$OUTPUT_FILE"

Notes

• Codex uses GPT-5.2, providing genuinely different perspective from Claude
• Each call is stateless - no conversation continuity
• API costs apply per call
• Output may contain duplicates - parse accordingly
• Always redirect stdin from /dev/null. Even with a prompt passed as an argument, codex exec reads stdin; in a non-interactive/background Bash call with no TTY it blocks ("Reading additional input from stdin...") and the -o output file ends up empty with exit code 0. The simpler usage examples above omit </dev/null — add it to every invocation.