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🚦 Exit Codes

✅ Check mode (--check)

--check suppresses stdout and uses the truthiness of the transform result as the exit code.

Exit code Meaning
0 ✅ Result is truthy
1 ❌ Result is falsy

Truthiness table

Value Truthy?
null ❌ falsy
false ❌ falsy
0, 0.0 ❌ falsy
"" ❌ falsy
[], {} ❌ falsy
Everything else ✅ truthy 
# ✅ Validate a record
fimod s -i record.json -e 'data.get("email") and data.get("name")' --check

# 🔀 In a shell conditional
if fimod s -i config.json -m validate.py --check; then
    echo "✅ Config is valid"
else
    echo "❌ Config has errors" >&2
    exit 1
fi

🚦 set_exit(code)

set_exit(code) sets the process exit code from inside a mold:

  • code is an integer 0–255
  • The mold continues executing to completion after the call
  • Returns None
def transform(data, args, env, headers):
    if not data.get("valid"):
        set_exit(1)
    return data

🔀 Interaction between set_exit and --check

set_exit takes priority

When both are active, set_exit overrides --check for the exit code. Stdout is still suppressed by --check.

# set_exit(2) inside validate.py overrides --check truthiness
fimod s -i record.json -m validate.py --check
echo $?   # could be 2, not 0 or 1

Advanced: specific exit codes per validation failure

# validate.py
def transform(data, args, env, headers):
    if "host" not in data:
        set_exit(2)   # 🔴 missing required field
        return data
    if not data.get("port"):
        set_exit(3)   # 🟡 missing port
        return data
    return True       # ✅ --check sees truthy → exit 0

fimod s -i config.json -m validate.py --check
case $? in
    0) echo "✅ OK" ;;
    2) echo "❌ Missing host" >&2 ;;
    3) echo "⚠️  Missing port" >&2 ;;
esac