Thank you @ain and @JimB for pointing me in the right direction.
Based on the example provided at https://github.com/chzyer/readline/tree/master/example/readline-demo I was able to achieve the desired functionality.
The following code has to main commands newEntry
and newCategory
. If the user types newEntry
and than presses TAB he can choose from the available categories. The newCategory
command allow to add a new custom category which is immediately available the next time newEntry
is executed.
package main
import (
"io"
"log"
"strconv"
"strings"
"github.com/chzyer/readline"
)
// completer defines which commands the user can use
var completer = readline.NewPrefixCompleter()
// categories holding the initial default categories. The user can add categories.
var categories = []string{"Category A", "Category B", "Category C"}
var l *readline.Instance
func main() {
// Initialize config
config := readline.Config{
Prompt: "\033[31m»\033[0m ",
HistoryFile: "/tmp/readline.tmp",
AutoComplete: completer,
InterruptPrompt: "^C",
EOFPrompt: "exit",
HistorySearchFold: true,
}
var err error
// Create instance
l, err = readline.NewEx(&config)
if err != nil {
panic(err)
}
defer l.Close()
// Initial initialization of the completer
updateCompleter(categories)
log.SetOutput(l.Stderr())
// This loop watches for user input and process it
for {
line, err := l.Readline()
if err == readline.ErrInterrupt {
if len(line) == 0 {
break
} else {
continue
}
} else if err == io.EOF {
break
}
line = strings.TrimSpace(line)
// Checking which command the user typed
switch {
// Add new category
case strings.HasPrefix(line, "newCategory"):
// Remove the "newCategory " prefix (including space)
if len(line) <= 12 {
log.Println("newCategory <NameOfCategory>")
break
}
// Append everything that comes behind the command as the name of the new category
categories = append(categories, line[12:])
// Update the completer to make the new category available in the cmd
updateCompleter(categories)
// Program is closed when user types "exit"
case line == "exit":
goto exit
// Log all commands we don't know
default:
log.Println("Unknown command:", strconv.Quote(line))
}
}
exit:
}
// updateCompleter is updates the completer allowing to add new command during runtime. The completer is recreated
// and the configuration of the instance update.
func updateCompleter(categories []string) {
var items []readline.PrefixCompleterInterface
for _, category := range categories {
items = append(items, readline.PcItem(category))
}
completer = readline.NewPrefixCompleter(
readline.PcItem("newEntry",
items...,
),
readline.PcItem("newCategory"),
)
l.Config.AutoComplete = completer
}