Migration Guide: v1 to v2

v2 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 Issue 921 or consider sending a PR to help improve this guide.

Flags before args

In v2 flags must come before args. This is more POSIX-compliant. You may need to update scripts, user documentation, etc.

This will work:

cli hello --shout rick

This will not:

cli hello rick --shout

Import string changed

• OLD: import "github.com/urfave/cli"
• NEW: import "github.com/urfave/cli/v2"

Check each file for this and make the change.

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

Flag aliases are done differently

Change Name: "foo, f" to Name: "foo", Aliases: []string{"f"}

• OLD:

  cli.StringFlag{
          Name: "config, cfg"
  }
  

• NEW:

  cli.StringFlag{
          Name: "config",
          Aliases: []string{"cfg"},
  }
  

Sadly v2 doesn't warn you if a comma is in the name. (https://github.com/urfave/cli/issues/1103)

EnvVar is now a list (EnvVars)

Change EnvVar: "XXXXX" to EnvVars: []string{"XXXXX"} (plural).

• OLD:

  cli.StringFlag{
          EnvVar: "APP_LANG"
  }
  

• NEW:

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

Actions returns errors

A command's Action: now returns an error.

• OLD: Action: func(c *cli.Context) {
• NEW: Action: func(c *cli.Context) error {

Compiler messages you might see:

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

cli.Flag changed

cli.Flag is now a list of pointers.

What this means to you:

If you make a list of flags, add a & in front of each item. cli.BoolFlag, cli.StringFlag, etc.

• OLD:

          app.Flags = []cli.Flag{
                 cli.BoolFlag{
  

• NEW:

          app.Flags = []cli.Flag{
                 &cli.BoolFlag{
  

Compiler messages you might see:

    cli.StringFlag does not implement cli.Flag (Apply method has pointer receiver)

Commands are now lists of pointers

Occurrences of []Command have been changed to []*Command.

What this means to you:

Look for []cli.Command{} and change it to []*cli.Command{}

Example:

• OLD: var commands = []cli.Command{}
• NEW: var commands = []*cli.Command{}

Compiler messages you might see:

cannot convert commands (type []cli.Command) to type cli.CommandsByName
cannot use commands (type []cli.Command) as type []*cli.Command in assignment

Lists of commands should be pointers

If you are building up a list of commands, the individual items should now be pointers.

• OLD: cli.Command{
• NEW: &cli.Command{

Compiler messages you might see:

cannot use cli.Command literal (type cli.Command) as type *cli.Command in argument to

Appending Commands

Appending to a list of commands needs to be changed since the list is now pointers.

• OLD: commands = append(commands, *c)
• NEW: commands = append(commands, c)

Compiler messages you might see:

cannot use c (type *cli.Command) as type cli.Command in append

GlobalString, GlobalBool and its likes are deprecated

Use simply String instead of GlobalString, Bool instead of GlobalBool

BoolTFlag and BoolT are deprecated

BoolTFlag was a Bool Flag with its default value set to true and BoolT was used to find any BoolTFlag used locally, so both are deprecated.

• OLD:

cli.BoolTFlag{
        Name:   FlagName,
        Usage:  FlagUsage,
        EnvVar: "FLAG_ENV_VAR",
}

* NEW:

cli.BoolFlag{
        Name:   FlagName,
        Value:  true,
        Usage:  FlagUsage,
        EnvVar: "FLAG_ENV_VAR",
}

&cli.StringSlice{""} replaced with cli.NewStringSlice("")

Example:

• OLD:

Value: &cli.StringSlice{""},

* NEW:

Value: cli.NewStringSlice(""),
}

Replace deprecated functions

cli.NewExitError() is deprecated. Use cli.Exit() instead. (Staticcheck detects this automatically and recommends replacement code.)

Everything else

Compile the code and work through any errors. Most should relate to issues listed above.

Once it compiles, test the command. Review the output of -h or any help messages to verify they match the intended flags and subcommands. Then test the program itself.

If you find any issues not covered by this document please let us know by submitting a comment on Issue 921 so that others can benefit.