Migration Guide: v2 to v3

v3 has a number of breaking changes but converting is relatively straightforward: make the changes documented below then resolve any compiler errors. We hope this will be sufficient for most typical users.

If you find any issues not covered by this document, please post a comment on the discussion or consider sending a PR to help improve this guide.

New Import

=== "v2"

`import "github.com/urfave/cli/v2"`

=== "v3"

`import "github.com/urfave/cli/v3"`

Check each file for this and make the change.

Shell command to find them all: fgrep -rl github.com/urfave/cli/v2 *

New Names

cli.App

=== "v2"

```go
cli.App{
        // ...
}
```

=== "v3"

```go
cli.Command{
        // ...
}
```

cli.App.EnableBashCompletion

=== "v2"

```go
cli.App{
        EnableBashCompletion: true,
}
```

=== "v3"

```go
cli.Command{
        EnableShellCompletion: true,
}
```

cli.App.CustomAppHelpTemplate

=== "v2"

```go
cli.App{
        CustomAppHelpTemplate: "...",
}
```

=== "v3"

```go
cli.Command{
        CustomRootCommandHelpTemplate: "...",
}
```

cli.App.RunContext

=== "v2"

```go
(&cli.App{}).RunContext(context.Background(), os.Args)
```

=== "v3"

```go
(&cli.Command{}).Run(context.Background(), os.Args)
```

cli.App.BashComplete

=== "v2"

```go
cli.App{
        BashComplete: func(ctx *cli.Context) {},
}
```

=== "v3"

```go
cli.Command{
        ShellComplete: func(ctx context.Context, cmd *cli.Command) {},
}
```

cli.Command.Subcommands

=== "v2"

```go
cli.Command{
        Subcommands: []*cli.Command{},
}
```

=== "v3"

```go
cli.Command{
        Commands: []*cli.Command{},
}
```

Sources

FilePath

=== "v2"

```go
cli.StringFlag{
        FilePath: "/path/to/foo",
}
```

=== "v3"

```go
cli.StringFlag{
        Sources: cli.Files("/path/to/foo"),
}
```

or 

```go
cli.StringFlag{
    Sources: cli.NewValueSourceChain(
        cli.File("/path/to/foo"),
    ),
}
```

EnvVars

=== "v2"

```go
cli.StringFlag{
        EnvVars: []string{"APP_LANG"},
}
```

=== "v3"

```go
cli.StringFlag{
        Sources: cli.EnvVars("APP_LANG"),
}
```

or 

```go
cli.StringFlag{
    Sources: cli.NewValueSourceChain(
       cli.EnvVar("APP_LANG"),
    ),
}
```

Altsrc

Altsrc is now a dedicated module

=== "v2"

`import "github.com/urfave/cli/v2/altsrc"`

=== "v3"

`import altsrc "github.com/urfave/cli-altsrc/v3"`

Altsrc is now a value source for CLI

=== "v2"

```go
altsrc.NewStringFlag(
    &cli.StringFlag{
        Name:        "key",
        Value:       "/tmp/foo",
    },
),
```

=== "v3"

Requires to use at least `github.com/urfave/cli-altsrc/[email protected]`

```go
cli.StringFlag{
    Sources: cli.NewValueSourceChain(altsrcjson.JSON("key", altsrc.StringSourcer("/path/to/foo.json"))),
}
```

Build Tags

v2 provided build tags to reduce binary size by stripping optional features:

Tag	Feature
`urfave_cli_no_docs`	Disabled markdown/man page generation
`urfave_cli_no_suggest`	Disabled "Did you mean?" suggestions

These tags are not available in v3 because they are no longer necessary:

Doc generation (ToMarkdown, ToMan) has been removed from the core library and is available as a separate module, github.com/urfave/cli-docs/v3.
Suggestions now use an inlined Jaro-Winkler algorithm with no external dependency (xrash/smetrics).
Shell completion uses embed.FS for its scripts, with no external dependencies.
Altsrc has been extracted to a separate module, github.com/urfave/cli-altsrc/v3 (see below).

Binary size in v3 is managed through architectural simplification rather than build tags. v3's minimal dependency tree (only github.com/stretchr/testify in tests) means the core library contributes very little to your final binary.

Order of precedence of envvars, filepaths, altsrc now depends on the order in which they are defined

=== "v2"

```go
altsrc.NewStringFlag(
    &cli.StringFlag{
        Name:     "key",
        EnvVars:  []string{"APP_LANG"},
        FilePath: "/path/to/foo",
    },
),
```

=== "v3"

Requires to use at least `github.com/urfave/cli-altsrc/[email protected]` 

```go
import altsrcjson "github.com/urfave/cli-altsrc/v3/json"

// ...

&cli.StringFlag{
    Name: "key",
    Sources: cli.NewValueSourceChain(
        cli.EnvVar("APP_LANG"),
        cli.File("/path/to/foo"),
        altsrcjson.JSON("key", altsrc.StringSourcer("/path/to/foo.json")),
    ),
},
```

In the above case the Envs are checked first and if not found then files are looked at and then finally the altsrc

cli.Context has been removed

All functions handled previously by cli.Context have been incorporated into cli.Command:

v2	v3
`cli.Context.IsSet`	`cli.Command.IsSet`
`cli.Context.NumFlags`	`cli.Command.NumFlags`
`cli.Context.FlagNames`	`cli.Command.FlagNames`
`cli.Context.LocalFlagNames`	`cli.Command.LocalFlagNames`
`cli.Context.Lineage`	`cli.Command.Lineage`
`cli.Context.Count`	`cli.Command.Count`
`cli.Context.Value`	`cli.Command.Value`
`cli.Context.Args`	`cli.Command.Args`
`cli.Context.NArg`	`cli.Command.NArg`

Handler Function Signatures Changes

All handler functions now take at least 2 arguments a context.Context and a pointer to Cli.Command in addition to other specific args. This allows handler functions to utilize context.Context for blocking/time-specific operations and so on.

BeforeFunc

=== "v2"

`type BeforeFunc func(*Context) error`

=== "v3"

`type BeforeFunc func(context.Context, *cli.Command) (context.Context, error)`

AfterFunc

=== "v2"

`type AfterFunc func(*Context) error`

=== "v3"

`type AfterFunc func(context.Context, *cli.Command) error`

ActionFunc

=== "v2"

`type ActionFunc func(*Context) error`

=== "v3"

`type ActionFunc func(context.Context, *cli.Command) error`

CommandNotFoundFunc

=== "v2"

`type CommandNotFoundFunc func(*Context, string) error`

=== "v3"

`type CommandNotFoundFunc func(context.Context, *cli.Command, string) error`

OnUsageErrorFunc

=== "v2"

`type OnUsageErrorFunc func(*Context, err error, isSubcommand bool) error`

=== "v3"

`type OnUsageErrorFunc func(context.Context, *cli.Command, err error, isSubcommand bool) error`

InvalidAccessFunc

=== "v2"

`type InvalidAccessFunc func(*Context, string) error`

=== "v3"

`type InvalidAccessFunc func(context.Context, *cli.Command, string) error`

ExitErrHandlerFunc

=== "v2"

`type ExitErrHandlerFunc func(*Context, err error) error`

=== "v3"

`type ExitErrHandlerFunc func(context.Context, *cli.Command, err error) error`

Compiler messages you might see(for ActionFunc):

cannot use func literal (type func(*cli.Context) error) as type cli.ActionFunc in field value

Similar messages would be shown for other funcs.

TimestampFlag

=== "v2"

```go
&cli.TimestampFlag{
    Name:   "foo",
    Layout: time.RFC3339,
}
```

=== "v3"

```go
&cli.TimestampFlag{
    Name:  "foo",
    Config: cli.TimestampConfig{
        Layouts: []string{time.RFC3339},
    },
}
```

PathFlag

=== "v2"

```go
&cli.PathFlag{
    Name:   "foo",
}
```

=== "v3"

```go
&cli.StringFlag{
    Name:  "foo",
    TakesFile: true,
}
```

Authors

=== "v2"

```go
&cli.App{
    Authors: []*cli.Author{
        {Name: "Some Guy", Email: "[email protected]"},
    },
}
```

=== "v3"

```go
// import "net/mail"
&cli.Command{
    Authors: []any{
        mail.Address{Name: "Some Guy", Address: "[email protected]"},
    },
}
```