README
¶
warg
Build hierarchical CLI applications with warg!
- warg uses funcopt style declarative APIs to keep CLIs readable (nested commands can be indented!) and terse. warg does not require code generation.
- warg is extremely interested in getting information into your app. Ensure a flag can be set from an environmental variable, configuration file, or default value by adding a single line to the flag declaration (configuration files also take some app-level config).
- warg is customizable. Add new types of flag values, config file formats, or --help outputs using the public API.
- Warg is easy to integrate into or remove from an existing codebase. This follows mostly from warg being terse and declarative. If you decide to remove warg, simply remove the app declaration and turn the passed flags into other types of function arguments for your command handlers. Done!
Examples
Full code for this example at ./examples/butler/main.go. Also see the godocs examples and other apps in the examples directory.
app := warg.New(
"butler",
section.New(
section.HelpShort("A virtual assistant"),
section.Command(
"present",
"Formally present a guest (guests are never introduced, always presented).",
present,
command.Flag(
"--name",
"Guest to address.",
scalar.String(),
flag.Alias("-n"),
flag.EnvVars("BUTLER_PRESENT_NAME", "USER"),
flag.Required(),
),
),
section.Command("version", "Print version", command.PrintVersion),
),
)
Run Butler
Color can be toggled on/off/auto with the --color flag:
The default help for a command dynamically includes each flag's current value and how it was was set (passed flag, config, envvar, app default).
Of course, running it with the flag also works
Apps Using Warg
- fling - GNU Stow replacement to manage my dotfiles
- grabbit - Grab images from Reddit
- starghaze - Save GitHub Starred repos to GSheets, Zinc
Should You Use warg?
I'm using warg for my personal projects, but the API is not finalized and there are some known issues (see below). I will eventually improve warg, but I'm currently ( 2021-11-19 ) taking a break from developing on warg to develop some CLIs with warg.
Known Issues / Design Tradeoffs
- lists containing aggregate values ( values in list objects from configs ) should be checked to have the same size and source but that must currently be done by the application ( see grabbit )
- By design, warg does not support positional arguments. Instead, use required flags. See "Unsupported CLI Patterns" below.
- By design, warg requires at least one subcommand. This makes adding additional subcommands easy. See "Unsupported CLI Patterns" below.
Alternatives
- cobra is by far the most popular CLI framework for Go. It relies on codegen.
- cli is also very popular.
- I've used the now unmaintained kingpin fairly successfully.
Concepts
Sections, Commands, Flags, and Values
warg is designed to create hierarchical CLI applications similar to azure-cli (just to be clear, azure-cli is not built with warg, but it was my inspiration for warg). These apps use sections to group subcommands, and pass information via flags, not positional arguments. A few examples:
azure-cli
az keyvault certificate create --name <name> --vault-name <vault-name> --tag <key1=value1> --tag <key2=value2>
If we try to dissect the parts of this command, we see that it:
- Starts with the app name (
az). - Narrows down intent with a section (
keyvault). Sections are usually nouns and function similarly to a directory hierarchy on a computer - used to group related sections and commands so they're easy to find and use together. - Narrows down intent further with another section (
certificate). - Ends with a command (
create). Commands are usually verbs and specify a single action to take within that section. - Passes information to the command with flags (
--name,--vault-name). - Each flag is passed exactly one value (
<name>,<vault-name>, and<key=valueare placeholders for user-specified values). A flag can be typed multiple times to build aggregate data structures like slices or maps.
This structure is both readable and scalable. az makes hundreds of commands browsable with this strategy!
grabbit
grabbit is a much smaller app to download wallpapers from Reddit that IS built with warg. It still benefits from the sections/commands/flags structure. Let's organize some of grabbit's components into a tree diagram:
grabbit # app name
├── --color # section flag
├── --config-path # section flag
├── --help # section flag
├── config # section
│ └── edit # command
│ └── --editor # command flag
├── grab # command
│ └── --subreddit-name # command flag
└── version # command
Similar to az, grabbit organizes its capabilities with sections, commands and flags. Sections are used to group commands. Flags defined in a "parent" section are available to child commands. for example, the config edit command has access to the parent --config-path flag, as does the grab command.
Populating Values
Values can be populated from app defaults, and these can be overridden by environmental variables, and these can be overridden by values read from a config , and, finally, these can be overriden by values passed when invoking the app on the command line via CLI flags.
Specify type-independent options to populate values with FlagOpts and type-specific value options with options specific to each type of value (such as slices or scalars).
See an example.
Specially Handled Flags
--config
Because warg has the capability to read values from a config file into the app, and then override those values from other sources, a--config flag must be parsed before other flags. See the docs for API and an example.
--help and --color
As a special case, the--help/-h flag may be passed without a value. If so, the default help action will be taken. See OverrideHelpFlag and its example for how to change the default help action. By convention, the built-in help commands look for a flag called --color to control whether --help prints to the terminal in color. Use AddColorFlag to easily add this flag to apps and ConditionallyEnableColor to easily look for this flag in custom help.
Unsupported CLI Patterns
One of warg's tradeoffs is that it insists on only using sections, commands, flags, and values. This means it is not possible (by design) to build some styles of CLI apps. warg does not support positional arguments. Instead, use a required flag: git clone <url> would be git clone --url <url>.
All warg apps must have at least one nested command. It is not possible to design a warg app such that calling <appname> --flag <value> does useful work. Instead, <appname> <command> --flag <value> must be used.
Documentation
¶
Overview ¶
Declaratively create heirarchical command line apps.
Index ¶
Examples ¶
Constants ¶
This section is empty.
Variables ¶
This section is empty.
Functions ¶
func ColorFlag ¶ added in v0.0.21
ColorFlag returns a flag indicating whether use user wants colored output. By convention, if this flag is named "--color", it will be respected by the different help commands. Usage:
section.ExistingFlag("--color", warg.ColorFlag()),
func GoldenTest ¶ added in v0.0.18
func GoldenTest( t *testing.T, args GoldenTestArgs, parseOpts ...ParseOpt)
GoldenTest runs the app and and captures stdout and stderr into files. If those differ than previously captured stdout/stderr, t.Fatalf will be called.
Passed `parseOpts` should not include OverrideStderr/OverrideStdout as GoldenTest overwrites those
func VersionCommand ¶ added in v0.0.21
Types ¶
type App ¶
type App struct {
// contains filtered or unexported fields
}
An App contains your defined sections, commands, and flags Create a new App with New()
func New ¶
New builds a new App!
Example ¶
package main
import (
"fmt"
"os"
"go.bbkane.com/warg"
"go.bbkane.com/warg/command"
"go.bbkane.com/warg/flag"
"go.bbkane.com/warg/section"
"go.bbkane.com/warg/value/scalar"
)
func login(ctx command.Context) error {
url := ctx.Flags["--url"].(string)
// timeout doesn't have a default value,
// so we can't rely on it being passed.
timeout, exists := ctx.Flags["--timeout"]
if exists {
timeout := timeout.(int)
fmt.Printf("Logging into %s with timeout %d\n", url, timeout)
return nil
}
fmt.Printf("Logging into %s\n", url)
return nil
}
func main() {
app := warg.New(
"newAppName",
section.New(
"work with a fictional blog platform",
section.Command(
"login",
"Login to the platform",
login,
),
section.Flag(
"--timeout",
"Optional timeout. Defaults to no timeout",
scalar.Int(),
),
section.Flag(
"--url",
"URL of the blog",
scalar.String(
scalar.Default("https://www.myblog.com"),
),
flag.EnvVars("BLOG_URL"),
),
section.Section(
"comments",
"Deal with comments",
section.Command(
"list",
"List all comments",
// still prototyping how we want this
// command to look,
// so use a provided stub action
command.DoNothing,
),
),
),
)
// normally we would rely on the user to set the environment variable,
// bu this is an example
err := os.Setenv("BLOG_URL", "https://envvar.com")
if err != nil {
fmt.Fprintln(os.Stderr, err)
os.Exit(1)
}
app.MustRun(warg.OverrideArgs([]string{"blog.exe", "login"}))
}
Output: Logging into https://envvar.com
func (*App) MustRun ¶
MustRun runs the app. Any flag parsing errors will be printed to stderr and os.Exit(64) (EX_USAGE) will be called. Any errors on an Action will be printed to stderr and os.Exit(1) will be called.
func (*App) Parse ¶
func (app *App) Parse(opts ...ParseOpt) (*ParseResult, error)
Parse parses the args, but does not execute anything.
Example (Flag_value_options) ¶
ExampleApp_Parse_flag_value_options shows a couple combinations of flag/value options. It's also possible to use '--help detailed' to see the current value of a flag and what set it.
package main
import (
"fmt"
"log"
"os"
"go.bbkane.com/warg"
"go.bbkane.com/warg/command"
"go.bbkane.com/warg/config/yamlreader"
"go.bbkane.com/warg/flag"
"go.bbkane.com/warg/section"
"go.bbkane.com/warg/value/scalar"
"go.bbkane.com/warg/value/slice"
)
func main() {
action := func(ctx command.Context) error {
// flag marked as Required(), so no need to check for existance
scalarVal := ctx.Flags["--scalar-flag"].(string)
// flag might not exist in config, so check for existance
// TODO: does this panic on nil?
sliceVal, sliceValExists := ctx.Flags["--slice-flag"].([]int)
fmt.Printf("--scalar-flag: %#v\n", scalarVal)
if sliceValExists {
fmt.Printf("--slice-flag: %#v\n", sliceVal)
} else {
fmt.Printf("--slice-flag value not filled!\n")
}
return nil
}
app := warg.New(
"flag-overrides",
section.New(
"demo flag overrides",
section.Command(
command.Name("show"),
"Show final flag values",
action,
command.Flag(
"--scalar-flag",
"Demo scalar flag",
scalar.String(
scalar.Choices("a", "b"),
scalar.Default("a"),
),
flag.ConfigPath("args.scalar-flag"),
flag.Required(),
),
command.Flag(
"--slice-flag",
"Demo slice flag",
slice.Int(
slice.Choices(1, 2, 3),
),
flag.Alias("-slice"),
flag.ConfigPath("args.slice-flag"),
flag.EnvVars("SLICE", "SLICE_ARG"),
),
),
),
warg.ConfigFlag(
"--config",
[]scalar.ScalarOpt[string]{
scalar.Default("~/.config/flag-overrides.yaml"),
},
yamlreader.New,
"path to YAML config file",
flag.Alias("-c"),
),
)
err := os.WriteFile(
"testdata/ExampleFlagValueOptions/config.yaml",
[]byte(`args:
slice-flag:
- 1
- 2
- 3
`),
0644,
)
if err != nil {
log.Fatalf("write error: %e", err)
}
app.MustRun(
warg.OverrideArgs([]string{"calc", "-c", "testdata/ExampleFlagValueOptions/config.yaml", "show", "--scalar-flag", "b"}),
)
}
Output: --scalar-flag: "b" --slice-flag: []int{1, 2, 3}
type AppOpt ¶
type AppOpt func(*App)
AppOpt let's you customize the app. Most AppOpts panic if incorrectly called
func ConfigFlag ¶
func ConfigFlag( configFlagName flag.Name, scalarOpts []scalar.ScalarOpt[string], newConfigReader config.NewReader, helpShort flag.HelpShort, flagOpts ...flag.FlagOpt, ) AppOpt
Use ConfigFlag in conjunction with flag.ConfigPath to allow users to override flag defaults with values from a config. This flag will be parsed and any resulting config will be read before other flag value sources.
Example ¶
package main
import (
"fmt"
"log"
"os"
"go.bbkane.com/warg"
"go.bbkane.com/warg/command"
"go.bbkane.com/warg/config/yamlreader"
"go.bbkane.com/warg/flag"
"go.bbkane.com/warg/section"
"go.bbkane.com/warg/value/scalar"
"go.bbkane.com/warg/value/slice"
)
func exampleConfigFlagTextAdd(ctx command.Context) error {
addends := ctx.Flags["--addend"].([]int)
sum := 0
for _, a := range addends {
sum += a
}
fmt.Printf("Sum: %d\n", sum)
return nil
}
func main() {
app := warg.New(
"newAppName",
section.New(
"do math",
section.Command(
command.Name("add"),
"add integers",
exampleConfigFlagTextAdd,
command.Flag(
flag.Name("--addend"),
"Integer to add. Flag is repeatible",
slice.Int(),
flag.ConfigPath("add.addends"),
flag.Required(),
),
),
),
warg.ConfigFlag(
"--config",
[]scalar.ScalarOpt[string]{
scalar.Default("~/.config/calc.yaml"),
},
yamlreader.New,
"path to YAML config file",
flag.Alias("-c"),
),
)
err := os.WriteFile(
"testdata/ExampleConfigFlag/calc.yaml",
[]byte(`add:
addends:
- 1
- 2
- 3
`),
0644,
)
if err != nil {
log.Fatalf("write error: %e", err)
}
app.MustRun(
warg.OverrideArgs([]string{"calc", "-c", "testdata/ExampleConfigFlag/calc.yaml", "add"}),
)
}
Output: Sum: 6
func OverrideHelpFlag ¶
func OverrideHelpFlag( mappings []help.HelpFlagMapping, defaultChoice string, flagName flag.Name, flagHelp flag.HelpShort, flagOpts ...flag.FlagOpt, ) AppOpt
OverrideHelpFlag customizes your --help. If you write a custom --help function, you'll want to add it to your app here!
Example ¶
package main
import (
"fmt"
"go.bbkane.com/warg"
"go.bbkane.com/warg/command"
"go.bbkane.com/warg/flag"
"go.bbkane.com/warg/help"
"go.bbkane.com/warg/help/common"
"go.bbkane.com/warg/help/detailed"
"go.bbkane.com/warg/section"
)
func exampleOverrideHelpFlaglogin(_ command.Context) error {
fmt.Println("Logging in")
return nil
}
func exampleOverrideHelpFlagCustomCommandHelp(_ *command.Command, _ common.HelpInfo) command.Action {
return func(ctx command.Context) error {
file := ctx.Stdout
fmt.Fprintln(file, "Custom command help")
return nil
}
}
func exampleOverrideHelpFlagCustomSectionHelp(_ *section.SectionT, _ common.HelpInfo) command.Action {
return func(ctx command.Context) error {
file := ctx.Stdout
fmt.Fprintln(file, "Custom section help")
return nil
}
}
func main() {
app := warg.New(
"newAppName",
section.New(
"work with a fictional blog platform",
section.Command(
"login",
"Login to the platform",
exampleOverrideHelpFlaglogin,
),
),
warg.OverrideHelpFlag(
[]help.HelpFlagMapping{
{
Name: "default",
CommandHelp: detailed.DetailedCommandHelp,
SectionHelp: detailed.DetailedSectionHelp,
},
{
Name: "custom",
CommandHelp: exampleOverrideHelpFlagCustomCommandHelp,
SectionHelp: exampleOverrideHelpFlagCustomSectionHelp,
},
},
"default",
"--help",
"Print help",
flag.Alias("-h"),
// the flag default should match a name in the HelpFlagMapping
),
)
app.MustRun(warg.OverrideArgs([]string{"blog.exe", "-h", "custom"}))
}
Output: Custom section help
func OverrideVersion ¶ added in v0.0.21
OverrideVersion lets you set a custom version string. The default is read from debug.BuildInfo
func SkipValidation ¶ added in v0.0.13
func SkipValidation() AppOpt
SkipValidation skips (most of) the app's internal consistency checks when the app is created. If used, make sure to call app.Validate() in a test!
type GoldenTestArgs ¶ added in v0.0.23
type LookupFunc ¶
Look up keys (meant for environment variable parsing) - fulfillable with os.LookupEnv or warg.LookupMap(map)
func LookupMap ¶
func LookupMap(m map[string]string) LookupFunc
LookupMap loooks up keys from a provided map. Useful to mock os.LookupEnv when parsing
type ParseOpt ¶ added in v0.0.21
type ParseOpt func(*ParseOptHolder)
func AddContext ¶ added in v0.0.21
func OverrideArgs ¶ added in v0.0.21
func OverrideLookupFunc ¶ added in v0.0.21
func OverrideLookupFunc(lookup LookupFunc) ParseOpt
func OverrideStderr ¶ added in v0.0.18
func OverrideStdout ¶ added in v0.0.18
type ParseOptHolder ¶ added in v0.0.21
type ParseOptHolder struct {
Args []string
Context context.Context
LookupFunc LookupFunc
// Stderr will be passed to command.Context for user commands to print to.
// This file is never closed by warg, so if setting to something other than stderr/stdout,
// remember to close the file after running the command.
// Useful for saving output for tests. Defaults to os.Stderr if not passed
Stderr *os.File
// Stdout will be passed to command.Context for user commands to print to.
// This file is never closed by warg, so if setting to something other than stderr/stdout,
// remember to close the file after running the command.
// Useful for saving output for tests. Defaults to os.Stdout if not passed
Stdout *os.File
}
func NewParseOptHolder ¶ added in v0.0.21
func NewParseOptHolder(opts ...ParseOpt) ParseOptHolder
Source Files
Directories