terminal

go-terminal

Lightweight golang terminal library, for creating your own REPL's.

Features:

• session history
• redraw of line buffer upon resize
• common edit and movement commands:
  • Right/Left-arrow: move cursor one char at a time
  • Up/Down-arrow: cycle through history
  • Backspace: works as expected
  • Ctrl-a or Home: move to start of line
  • Ctrl-e or End: move to end of line
  • Ctrl-w: delete preceding word
  • Ctrl-v: paste contents of xclip (only linux, only if installed)
  • Ctrl + Right/Left-arrow: move cursor one word at a time
  • Ctrl-c or Esc: ignore line
  • Ctrl-d: quit
  • Ctrl-u: clear line to start
  • Ctrl-l: clear screen

Usage

Fetch this library with the following command:

$ go get -u github.com/openengineer/go-terminal

In order to create your own REPL you have to define a type that implements the Handler interface:

type Handler interface {
  Eval(line string) (out string, hist string)
}

Here is a complete example (can also be found in ./examples/simple/main.go):

package main

import (
  "fmt"
  "log"
  "strconv"
  "strings"

  terminal "github.com/openengineer/go-terminal"
)

var helpMessage = `help: display this message
add <int> <int>: add two numbers`

// implements terminal.Handler interface
type REPL struct {
}

func main() {
  fmt.Println("Welcome, type \"help\" for more info")

  repl := &REPL{}

  t := terminal.NewTerminal(repl)
  t.SetPrompt("$") // default is ">", terminal always adds one space after the prompt

  // start the terminal loop
  if err := t.Run(); err != nil {
    log.Fatal(err)
  }
}

// first return value is for stdout, second return value is for history
func (r *REPL) Eval(line string) (string, string) {
  fields := strings.Fields(line)

  if len(fields) == 0 {
    return "", ""
  } else {
    cmd, args := fields[0], fields[1:]

    switch cmd {
    case "help":
      return helpMessage, line
    case "add":
      if len(args) != 2 {
        return "\"add\" expects 2 args", line
      } else {
        return add(args[0], args[1]), line
      }
    default:
      return fmt.Sprintf("unrecognized command \"%s\"", cmd), line
    }
  }
}

func add(a_ string, b_ string) string {
  a, err := strconv.Atoi(a_)
  if err != nil {
    return "first arg is not an integer"
  }

  b, err := strconv.Atoi(b_)
  if err != nil {
    return "second arg is not an integer"
  }

  return strconv.Itoa(a + b)
}