feat: Open-source semantic exit codes

LICENSE

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README.md

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+# Semantic Exit Codes
+
+### Usage
+
+#### Go
+
+```golang
+os.Exit(exit.Forbidden) // The user isn't permitted to perform this action
+os.Exit(exit.Unavailable) // An API this program consumes isn't available
+```
+
+See [the complete list of exit codes](#the-codes).
+
+### About
+
+Conventionally, exiting a program with zero indicates success while nonzero indicates failure.
+
+```golang
+os.Exit(0) // success
+os.Exit(1) // failure
+```
+
+But the system call `exit` accepts values between 0 and 255, leaving 254 different ways of expressing failure.
+
+This library's goals are to define exit codes that are:
+1. Broadly applicable to heterogenous Command Line tools
+2. Easy to partition into user errors and system errors
+
+It defines codes in two [unreserved](#reserved-codes-and-prior-art) ranges: 80-99 for user errors and 100-119 for software or system errors.
+
+### The Codes
+
+| Exit Code | Name | Meaning |
+| --: | :-- | :-- |
+| 0 | `OK` | The program exited successfully. |
+| 1 | `NotOK` | The program exited unsuccessfully but gives no extra context as to what the failure was. |
+| 80 | `UsageError` | The program exited unsuccessfully because it was was used incorrectly. (e.g. a required argument was omitted or an invalid value was supplied for a flag.) |
+| 81 | `UnknownSubcommand` | The program exited unsuccessfully because an unrecognized subcommand was invoked. (Used by CLI multi-tools.) |
+| 82 | `RequirementNotMet` | The program exited unsuccessfully because a prerequisite of it wasn't met. |
+| 83 | `Forbidden` | The program exited unsuccessfully because the user isn't authorized to perform the requested action. |
+| 84 | `MovedPermanently` | The program exited unsuccessfully because it has been migrated to a new location. |
+| 100 | `InternalError` | The program exited unsuccessfully because of a problem in its own code. (Used instead of 1 when the problem is known to be with the program's code or dependencies.) |
+| 101 | `Unavailable` | The program exited unsuccessfully because a service it depends on was not available. (e.g. A local daemon or remote service did not respond, a connection was closed unexpectedly, an HTTP service responded with 503.) |
+
+### Reserved Codes and Prior Art
+
+- Values above 128 are reserved for signals. (When a program is terminated with a signal, its exit code is 128 + the signal's numeric value. When you terminate a program with `Ctrl` `C`, for example, you send it the signal `SIGINT` — whose value is 2 — and the program exits with 130.) 
+- Bash [reserves 2, 126, and 127](https://tldp.org/LDP/abs/html/exitcodes.html).
+- [sysexits.h defines 64-78](https://github.com/bminor/glibc/blob/master/misc/sysexits.h#L96-L110). The `sysexits.h` codes were originally defined for `sendmail` but have been used many places since. ([Compare Semantic Exit Codes to sysexits.h codes](https://github.com/square/exit/wiki/Comparison-to-sysexits.h-Exit-Codes))

exit.go

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+/*
+Package exit defines semantic exit codes which may be used by Command Line tools
+to aid in debugging and instrumentation.
+
+This package defines exit codes in two ranges. Exit Codes 80-99 indicate a user error
+of some sort. Exit Codes 100-119 indicate software or system error of some sort.
+*/
+package exit
+
+// Code is the exit code that is passed to the system call `exit`
+// when the program terminates. Conventionally, the value zero indicates
+// success and all other values (1-255) indicate failure.
+type Code = int
+
+const (
+	// OK indicates that the program exited successfully.
+	OK Code = 0
+
+	// NotOK indicates that the program exited unsuccessfully
+	// but gives no extra context as to what the failure was.
+	NotOK Code = 1
+)
+
+// Exit Codes 80-99 are reserved for user errors.
+const (
+	// UsageError indicates that the program exited unsuccessfully
+	// because it was was used incorrectly.
+	//
+	// Examples: a required argument was omitted or an invalid value
+	// was supplied for a flag.
+	UsageError Code = 80
+
+	// UnknownSubcommand indicates that the program exited unsuccessfully
+	// because an unrecognized subcommand was invoked.
+	//
+	// This is intended for CLI multi-tools. When you run a command that
+	// doesn't exist from the shell, the shell exits 127. This is distinct
+	// from that value in that the command itself exists but the subcommand
+	// does not (e.g. `git nope` could exit 81).
+	UnknownSubcommand Code = 81
+
+	// RequirementNotMet indicates that the program exited unsuccessfully
+	// because a precondition wasn't satisfied.
+	//
+	// Examples: the user must be on a VPN before using the program or have
+	// a minimum version of some other software installed.
+	RequirementNotMet Code = 82
+
+	// Forbidden indicates that the program exited unsuccessfully
+	// because the user isn't authorized to perform the requested action.
+	Forbidden Code = 83
+
+	// MovedPermanently indicates that the program exited unsuccessfully
+	// because it has been migrated to a new location.
+	MovedPermanently Code = 84
+)
+
+// Exit Codes 100-119 are reserved for software or system errors.
+const (
+	// InternalError indicates that the program exited unsuccessfully
+	// because of a problem in its own code.
+	//
+	// Used instead of 1 when the problem is known to be with the program's
+	// code or dependencies.
+	InternalError Code = 100
+
+	// Unavailable indicates that the program exited unsuccessfully
+	// because a service it depends on was not available.
+	//
+	// Examples: A local daemon or remote service did not respond, a connection
+	// was closed unexpectedly, an HTTP service responded with 503.
+	Unavailable Code = 101
+)
+
+// IsUserError reports whether an exit code is a user error.
+// It returns true if the code is in the range 80-99 and false if not.
+func IsUserError(code Code) bool {
+	return code >= 80 && code <= 99
+}
+
+// IsSoftwareError reports whether an exit code is a software error.
+// It returns true if the code is in the range 100-119 and false if not.
+func IsSoftwareError(code Code) bool {
+	return code >= 100 && code <= 119
+}
+
+// IsSignal reports whether an exit code is derived from a signal.
+// It returns true if the code is in the range 128-255 and false if not.
+// It also returns true if the code is -1 because ProcessState.ExitCode()
+// may return -1 if the process was terminated by a signal.
+func IsSignal(code Code) bool {
+	// -1 is not a valid exit code, but ProcessState.ExitCode()
+	// may return -1 if the process was terminated by a signal.
+	//
+	// https://pkg.go.dev/os#ProcessState.ExitCode
+	return code == -1 || code > 128 && code < 255
+}

go.mod

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+module github.com/square/exit
+
+go 1.19