This is subcmd, a Go package for writing command-line programs that require flag parsing and that have “subcommands” that also require flag parsing.
Use it when you want your program to parse command lines that look like this:
command -globalopt subcommand -subopt1 FOO -subopt2 ARG1 ARG2
Subcommands may have sub-subcommands and so on. Subcommands may also be implemented as separate executables. (See the documentation for Prefixer.)
This is a layer on top of the standard Go flag
package.
func main() {
// Parse global flags normally.
dbname := flag.String("db", "", "database connection string")
flag.Parse()
db, err := sql.Open(dbdriver, *dbname)
if err != nil { ... }
// Stash global options in a top-level command object.
c := command{db: db}
// Run the subcommand given in the remainder of the command line.
err = subcmd.Run(context.Background(), c, flag.Args())
if err != nil { ... }
}
// The top-level command object.
type command struct {
db *sql.DB
}
// To be used in subcmd.Run above, `command` must implement this method.
func (c command) Subcmds() subcmd.Map {
return subcmd.Commands(
// The "list" subcommand takes one flag, -reverse.
"list", c.list, "list employees", subcmd.Params(
"-reverse", subcmd.Bool, false, "reverse order of list",
),
// The "add" subcommand takes no flags but one positional argument.
"add", c.add, "add new employee", subcmd.Params(
"name", subcmd.String, "", "employee name",
)
)
}
// Implementation of the "list" subcommand.
// The value of the -reverse flag is passed as an argument.
func (c command) list(ctx context.Context, reverse bool, _ []string) error {
query := "SELECT name FROM employees ORDER BY name"
if reverse {
query += " DESC"
}
rows, err := c.db.QueryContext(ctx, query)
if err != nil { ... }
defer rows.Close()
for rows.Next() { ... }
return rows.Err()
}
// Implementation of the "add" subcommand.
func (c command) add(ctx context.Context, name string, _ []string) error {
_, err := c.db.ExecContext(ctx, "INSERT INTO employees (name) VALUES ($1)", name)
return err
}