CLI tools should use both. Return an exit status so shells and scripts can reliably decide whether to continue, retry, or stop; provide a diagnostic with useful context so people and automation can understand what failed. Keep the status taxonomy small, make structured output predictable, and document how the two channels relate.
What each error channel is for
Exit status: the control-flow signal
A process exit status is the compact result a shell can use directly. POSIX.1-2024 says each command has an exit status that can influence other shell commands. In the usual convention, zero means success and nonzero means failure. That convention is useful for shell conditionals and pipelines, but a status alone usually cannot explain a domain-specific problem.
POSIX also specifies important command-launch cases: status 127 when a command is not found, 126 when it is found but not executable, and a value greater than 128 for termination by a signal. The signal-identification behavior is implementation-defined. These conventions do not establish a universal mapping for every application error. GNU Coreutils notes that nonzero is typically 1, but individual utilities may define exceptions.
Structured diagnostic: the explanation
A structured diagnostic can carry a stable error kind or code, a concise message, and relevant context such as a missing setting or a service-provided error type. That gives people enough information to act and gives scripts fields they can inspect without trying to parse prose. AWS CLI documents error output on stderr and shows fields such as Code and Message; some service errors can also include a modeled Type.
Free tools Windows power users keep installed
One-click scans. No signup required.
#1 Best Overall
- Read Before You Buy — No Video Output: These adapters support charging and USB 2.0 data transfer, but cannot transmit video signals. Except for standard USB webcams (which use USB data only), they are not compatible with HDMI/DisplayPort cables, video-capable USB-C hubs, or docking stations with video output.
- Convert USB-A Ports to USB-C: Designed to connect USB-C earphones, cables, flash drives, card readers, and other USB-C accessories to standard USB-A ports. Plug-and-play with no drivers or software required.
- Aluminum Alloy Housing: Built with a sturdy aluminum alloy shell that aids in heat dissipation and protects against daily wear and scratches. Designed to maintain a stable and secure connection.
- Compact & Travel-Friendly: The ultra-compact design allows the adapter to stay plugged into your device without blocking adjacent ports or adding bulk, reducing wear and tear on your original USB ports.
- 12-Month Warranty: Backed by a 12-month manufacturer warranty for peace of mind. Designed to meet strict quality control standards for reliable everyday performance.
The two channels complement each other: status answers whether the invocation succeeded, while the diagnostic explains the failure. Shopify CLI documents a version of this separation, treating the process exit code as the source of truth for success or failure while distinguishing execution-level failures from errors in a command’s result schema. That is an implementation choice, not a universal rule.
How the two approaches compare
| Criterion | Exit status | Structured diagnostic |
|---|---|---|
| Shell branching | Available directly to shell control flow. | Must be read and parsed from output. |
| Detail | Limited; callers need a documented mapping. | Can include an error kind, message, and contextual fields. |
| Human readability | A bare number says little; pair it with a diagnostic. | Can be rendered as readable text or, in a selected format, JSON or YAML. |
| Portability and conventions | Zero/nonzero conventions are widely used, but specific nonzero meanings vary. | Depends on a documented schema and selected output format. |
| Compatibility | Changing a code’s meaning can break scripts. | Changing field names or shape can break parsers; evolve the schema carefully. |
Design the contract between status and diagnostic
Keep statuses few, documented, and stable
Reserve zero for success and use nonzero when the command fails. If callers need to distinguish common categories—such as a usage error, configuration problem, or temporary failure—define a small, stable set and document it. Scripts should still handle an unknown nonzero status as failure rather than assuming every possible code is known.
Rank #2
- 5-in-1 USB-C Hub: Experience comprehensive connectivity featuring a Power Delivery input, two USB-A 2.0 ports, a USB-A 3.0 port, and an HDMI port. (Note: The USB-C power delivery input port is only for connecting an external wall charger to power your laptop and cannot power peripheral devices.)
- 90W Pass-Through Charging: Achieve optimal charging with 90W pass-through power to your laptop, supported by a total input of 100W, with the hub reserving 10W for operational efficiency. (Note: Wall charger not included.)
- Quick Data Transfers: Accelerate your productivity with rapid data transfers using a high-speed 5Gbps USB 3.0 port and two 480Mbps USB 2.0 ports.
- 4K HDMI Display: Enhance your visual experience with a hub capable of delivering 4K resolution at 30Hz in both mirror and extend modes. Please note that this hub is compatible with MacBook (macOS 12 and newer), Windows 10 and 11, ChromeOS, and laptops equipped with DP Alt Mode and Power Delivery. Note: This device is not compatible with Linux.
- What You Get: Anker USB-C Hub (5-in-1, 4K HDMI), welcome guide, 18-month warranty, and our friendly customer service.
The sysexits.h vocabulary offers examples: EX_USAGE is 64, EX_TEMPFAIL is 75, and EX_CONFIG is 78. These are conventions, not a mandatory taxonomy for every modern CLI. The Linux man-pages project’s sysexits.h(3head) notes that choosing an appropriate value is often ambiguous.
Put actionable detail in the diagnostic
Include a stable error kind or code, a concise human-readable message, and only the contextual fields that help explain or resolve the problem. For example, distinguish “configuration missing” from “access denied” with stable kinds, then include the relevant setting name or service detail where appropriate. Treat field names and meanings as part of the CLI’s public interface: changing them can break consumers just as changing exit-code meanings can.
Do these 3 things before closing this tab:
1Clear out junk files and repair common Windows errors2Scan for outdated or missing drivers - takes under a minute3Repair Windows errors before they cause bigger problemsRank #3
- Sleek 7-in-1 USB-C Hub: Features an HDMI port, two USB-A 3.0 ports, and a USB-C data port, each providing 5Gbps transfer speeds. It also includes a USB-C PD input port for charging up to 100W and dual SD and TF card slots, all in a compact design.
- Flawless 4K@60Hz Video with HDMI: Delivers exceptional clarity and smoothness with its 4K@60Hz HDMI port, making it ideal for high-definition presentations and entertainment. (Note: Only the HDMI port supports video projection; the USB-C port is for data transfer only.)
- Double Up on Efficiency: The two USB-A 3.0 ports and a USB-C port support a fast 5Gbps data rate, significantly boosting your transfer speeds and improving productivity.
- Fast and Reliable 85W Charging: Offers high-capacity, speedy charging for laptops up to 85W, so you spend less time tethered to an outlet and more time being productive.
- What You Get: Anker USB-C Hub (7-in-1), welcome guide, 18-month warranty, and our friendly customer service.
Keep results and diagnostics in deliberate streams
Where it fits the command’s output contract, write normal command results to stdout and diagnostics to stderr. This lets a caller redirect a result without accidentally capturing a human-facing error message alongside it. AWS CLI explicitly documents errors on stderr. If structured mode emits an error document, define whether it goes to stdout or stderr and how it behaves alongside the nonzero status; do not leave consumers to infer the contract.
Offer readable output and an explicit machine-readable mode
Do not force opaque JSON on every person at an interactive terminal. Offer a readable default and a predictable machine-readable option such as --json, with stable field names and documented behavior. The CLI Guidelines recommend human-readable output and machine-readable output where it does not harm usability, and advise formatted JSON when --json is passed. AWS CLI likewise offers human-oriented output as well as formats including JSON and YAML.
Rank #4
- Dual Converters, Infinite Potential：Includes 2× USB C male to USB A female adapters and 2× USB A male to USB C female adapters. Perfect for a wide range of uses—tablets with Bluetooth keyboards, expand USB ports on macbook, and more. Two different converters for all your daily needs
- Next-Level 10Gbps & 3A Charging: No more slow 480Mbps, this usb to usb c adapter has a transfer speed of up to 10Gbps, allowing you to do more transferring in less time. This usb adapter fits both USB A and USB C charger, supporting up to 3A fast charging
- Upgraded Exquisite Craftsmanship: With an aluminum alloy housing and metal connector, the usbc to usb adapter is extremely durable and sturdy. Rigorously tested to withstand more than 10,000 times of plugging and unplugging, ensuring long-lasting performance
- Broad Compatible: The usb c to usb adapter widely supports all USB C/ USB A devices like laptops, tablets, cellphones, car chargers, and phone chargers. Such as compatible with MacBook Pro/Air 2023/2022, Thunderbolt 4/3 Devices,Apple MagSafe Watch 9/8/7/SE/Ultra, iPad Pro 2022/2021, Samsung Galaxy S23/S20/S10, and iPhone 17/16/15 Pro. Plug and play
- Please Note: To reach 10Gbps speed, keep the cable under 3.3 ft. For USB A Male to USB C adapters, try flipping the USB C connector. USB C Male to USB A adapters support bidirectional 10Gbps transfer within 3.3 ft
Document what callers can rely on
A CLI’s error contract should tell users and scripts, in one place:
- Which condition counts as command success, and what zero and nonzero statuses mean.
- Whether statuses distinguish any documented failure categories, and that unknown nonzero statuses still indicate failure.
- Whether a diagnostic accompanies a nonzero exit, what fields it contains in structured mode, and which stream carries it.
- How to request machine-readable output and whether its schema is stable or versioned.
- Which failures are safe to retry, if the command can make that distinction. A nonzero status by itself does not tell a caller whether retrying is appropriate.
POSIX defines shell behavior and important command-launch statuses, not a complete application-error map. The sysexits.h values are useful vocabulary, but there is no single required assignment of every domain failure to a process status. A CLI’s own documentation must supply that relationship.
Quick Recap
Best Value
- 5-in-1 Connectivity: Equipped with a 4K HDMI port, a 5 Gbps USB-C data port, two 5 Gbps USB-A ports, and a USB C 100W PD-IN port. Note: The USB C 100W PD-IN port supports only charging and does not support data transfer devices such as headphones or speakers.
- Powerful Pass-Through Charging: Supports up to 85W pass-through charging so you can power up your laptop while you use the hub. Note: Pass-through charging requires a charger (not included). Note: To achieve full power for iPad, we recommend using a 45W wall charger.
- Transfer Files in Seconds: Move files to and from your laptop at speeds of up to 5 Gbps via the USB-C and USB-A data ports. Note: The USB C 5Gbps Data port does not support video output.
- HD Display: Connect to the HDMI port to stream or mirror content to an external monitor in resolutions of up to 4K@30Hz. Note: The USB-C ports do not support video output.
- What You Get: Anker 332 USB-C Hub (5-in-1), welcome guide, our worry-free 18-month warranty, and friendly customer service.
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
