diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..3d3982c
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,3 @@
+.idea
+*.swp
+build/
diff --git a/LICENSE b/LICENSE
new file mode 100644
index 0000000..ab60297
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2018 
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..9993f93
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,92 @@
+.DEFAULT_GOAL := help
+
+GOCMD := env GO111MODULE=on go
+GOMOD := $(GOCMD) mod
+GOBUILD := $(GOCMD) build
+GOINSTALL := $(GOCMD) install
+GOCLEAN := $(GOCMD) clean
+GOTEST := $(GOCMD) test
+GOGET := $(GOCMD) get
+NAME := dango
+CURRENT := $(shell pwd)
+BUILDDIR := ./build
+BINDIR := $(BUILDDIR)/bin
+PKGDIR := $(BUILDDIR)/pkg
+DISTDIR := $(BUILDDIR)/dist
+
+VERSION := $(shell git describe --tags --abbrev=0)
+LDFLAGS := -X 'main.version=$(VERSION)'
+GOXOSARCH := "darwin/amd64 darwin/arm64 windows/386 windows/amd64 linux/386 linux/amd64"
+GOXOUTPUT := "$(PKGDIR)/$(NAME)_{{.OS}}_{{.Arch}}/{{.Dir}}"
+
+export GO111MODULE=on
+
+.PHONY: deps
+## Install dependencies
+deps:
+	$(GOMOD) download
+
+.PHONY: devel-deps
+## Install dependencies for develop
+devel-deps: deps
+	sh -c '\
+	tmpdir=$$(mktemp -d); \
+	cd $$tmpdir; \
+	$(GOGET) \
+		golang.org/x/tools/cmd/goimports \
+		golang.org/x/lint/golint \
+		github.com/Songmu/make2help/cmd/make2help \
+		github.com/mitchellh/gox \
+		github.com/tcnksm/ghr; \
+	rm -rf $$tmpdir'
+
+.PHONY: build
+## Build binaries
+build: deps
+	$(GOBUILD) -ldflags "$(LDFLAGS)" -o $(BINDIR)/$(NAME) .
+
+.PHONY: cross-build
+## Cross build binaries
+cross-build:
+	rm -rf $(PKGDIR)
+	gox -osarch=$(GOXOSARCH) -ldflags "$(LDFLAGS)" -output=$(GOXOUTPUT) .
+
+.PHONY: package
+## Make package
+package: cross-build
+	rm -rf $(DISTDIR)
+	mkdir $(DISTDIR)
+	pushd $(PKGDIR) > /dev/null && \
+		for P in `ls | xargs basename`; do zip -r $(CURRENT)/$(DISTDIR)/$$P.zip $$P; done && \
+		popd > /dev/null
+
+.PHONY: release
+## Release package to Github
+release: package
+	ghr $(VERSION) $(DISTDIR)
+
+.PHONY: test
+## Run tests
+test: deps
+	$(GOTEST) -v ./...
+
+.PHONY: lint
+## Lint
+lint: devel-deps
+	go vet ./...
+	golint -set_exit_status ./...
+
+.PHONY: fmt
+## Format source codes
+fmt: deps
+	find . -name "*.go" -not -path "./vendor/*" | xargs goimports -w
+
+.PHONY: clean
+clean:
+	$(GOCLEAN)
+	rm -rf $(BUILDDIR)
+
+.PHONY: help
+## Show help
+help:
+	@make2help $(MAKEFILE_LIST)
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..8bd90ce
--- /dev/null
+++ b/README.md
@@ -0,0 +1,154 @@
+[English](README.md) | [日本語](README_ja.md)
+
+# 🍡 dango
+
+🍡`dango` is a program that concatenates and splits standard input.
+
+## Description
+
+`dango` concatenates and splits the standard input.
+
+`dango` concatenates and splits standard input by bytes, characters, words, or line breaks.
+`dango` reads the standard input and whenever it reads a specified number of elements, it puts them on a line and prints them to the standard output.
+
+## Usage
+
+```
+$ cat << EOF | dango
+━
+🟠
+🟡
+🟢
+━
+EOF
+━🟠🟡🟢━
+```
+
+Concatenate or split by number of bytes.
+
+```
+$ echo 'Hello World!' | dango -b -n 1
+H
+e
+l
+l
+o
+
+W
+o
+r
+l
+d
+!
+
+$ echo 'Hello World!' | dango -b -n 5
+Hello
+ Worl
+d!
+```
+
+Concatenate or split by number of characters.
+
+```
+$ echo '花より団子' | dango -c -n 1
+花
+よ
+り
+団
+子
+
+$ echo '花より団子' | dango -c -n 3
+花より
+団子
+```
+
+Concatenate or split by word count.
+
+```
+$ echo 'Hello World!' | dango -w -n 1
+Hello
+World!
+
+$ echo 'Hello World!' | dango -w
+HelloWorld!
+```
+
+Concatenate or split by the number of line breaks.
+
+```
+$ cat << EOF | dango -l -n 1
+Hello
+World!
+EOF
+Hello
+World!
+
+$ cat << EOF | dango -l
+Hello
+
+World
+
+!
+EOF
+HelloWorld!
+```
+
+Specify a delimiter to concatenate or split.
+
+```
+$ echo 'abcdefg' | dango -c -d ' '
+a b c d e f g 
+
+$ cat << EOF | dango -d ' '
+Hello
+World!
+EOF
+Hello World!
+```
+
+Show help.
+
+```
+$ dango -help
+# ...
+```
+
+## Installation
+
+### Developer
+
+Go 1.16 or later.
+
+```
+$ go install github.com/ebc-2in2crc/dango@latest
+```
+
+Go 1.15.
+
+```
+$ go get github.com/ebc-2in2crc/dango/...
+```
+
+### User
+
+Download from the following url.
+
+- [https://github.com/ebc-2in2crc/dango/releases](https://github.com/ebc-2in2crc/dango/releases)
+
+## Contribution
+
+1. Fork this repository
+2. Create your feature branch (git checkout -b my-new-feature)
+3. Commit your changes (git commit -am 'Add some feature')
+4. Rebase your local changes against the master branch
+5. Run test suite with the `make test` command and confirm that it passes
+6. Run `make fmt`
+7. Create new Pull Request
+
+## License
+
+[MIT](https://github.com/ebc-2in2crc/wareki/blob/master/LICENSE)
+
+## Author
+
+[ebc-2in2crc](https://github.com/ebc-2in2crc)
diff --git a/README_ja.md b/README_ja.md
new file mode 100644
index 0000000..7182df0
--- /dev/null
+++ b/README_ja.md
@@ -0,0 +1,154 @@
+[English](README.md) | [日本語](README_ja.md)
+
+# 🍡 dango
+
+🍡 `dango` は標準入力を連結したり分割するプログラムです。
+
+## Description
+
+`dango` は標準入力を連結したり分割します。
+
+`dango` は標準入力をバイト、文字、単語あるいは改行によって連結したり分割します。
+`dango` は標準入力を読み取って、読み取った要素が指定した数になるごとにそれを1行にまとめて、標準出力に出力します。
+
+## Usage
+
+```
+$ cat << EOF | dango
+━
+🟠
+🟡
+🟢
+━
+EOF
+━🟠🟡🟢━
+```
+
+バイト数で連結したり分割する。
+
+```
+$ echo 'Hello World!' | dango -b -n 1
+H
+e
+l
+l
+o
+
+W
+o
+r
+l
+d
+!
+
+$ echo 'Hello World!' | dango -b -n 5
+Hello
+ Worl
+d!
+```
+
+文字数で連結したり分割する。
+
+```
+$ echo '花より団子' | dango -c -n 1
+花
+よ
+り
+団
+子
+
+$ echo '花より団子' | dango -c -n 3
+花より
+団子
+```
+
+単語数で連結したり分割する。
+
+```
+$ echo 'Hello World!' | dango -w -n 1
+Hello
+World!
+
+$ echo 'Hello World!' | dango -w
+HelloWorld!
+```
+
+改行の数で連結したり分割する。
+
+```
+$ cat << EOF | dango -l -n 1
+Hello
+World!
+EOF
+Hello
+World!
+
+$ cat << EOF | dango -l
+Hello
+
+World
+
+!
+EOF
+HelloWorld!
+```
+
+デリミターを指定して連結したり分割する。
+
+```
+$ echo 'abcdefg' | dango -c -d ' '
+a b c d e f g 
+
+$ cat << EOF | dango -d ' '
+Hello
+World!
+EOF
+Hello World!
+```
+
+ヘルプ。
+
+```
+$ dango -help
+# ...
+```
+
+## Installation
+
+### Developer
+
+Go 1.16 以降。
+
+```
+$ go install github.com/ebc-2in2crc/dango@latest
+```
+
+Go 1.15。
+
+```
+$ go get github.com/ebc-2in2crc/dango/...
+```
+
+### User
+
+次の URL からダウンロードします。
+
+- [https://github.com/ebc-2in2crc/dango/releases](https://github.com/ebc-2in2crc/dango/releases)
+
+## Contribution
+
+1. Fork this repository
+2. Create your feature branch (git checkout -b my-new-feature)
+3. Commit your changes (git commit -am 'Add some feature')
+4. Rebase your local changes against the main branch
+5. Run test suite with the `make test` command and confirm that it passes
+6. Run `make fmt`
+7. Create new Pull Request
+
+## License
+
+[MIT](https://github.com/ebc-2in2crc/dango/blob/main/LICENSE)
+
+## Author
+
+[ebc-2in2crc](https://github.com/ebc-2in2crc)
diff --git a/cli.go b/cli.go
new file mode 100644
index 0000000..c14629b
--- /dev/null
+++ b/cli.go
@@ -0,0 +1,100 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+	"io"
+	"os"
+)
+
+type cli struct {
+	inStream             io.Reader
+	outStream, errStream io.Writer
+}
+
+type dangoOptions = struct {
+	size          int
+	delimiter     string
+	maxBufferSize int
+	lines         bool
+	words         bool
+	characters    bool
+	bytes         bool
+	version       bool
+	help          bool
+}
+
+var options dangoOptions
+
+func init() {
+	flag.IntVar(&options.maxBufferSize, "B", 0, "Maximum size used to buffer a token")
+	flag.BoolVar(&options.bytes, "b", false, "Concat or split standard input by bytes")
+	flag.BoolVar(&options.characters, "c", false, "Concat or split standard input by characters")
+	flag.StringVar(&options.delimiter, "d", "", "Element delimiter (default \"\")")
+	flag.BoolVar(&options.lines, "l", false, "Concat or split standard input by lines")
+	flag.IntVar(&options.size, "n", 0, "Number of elements in each line")
+	flag.BoolVar(&options.version, "version", false, "Show version")
+	flag.BoolVar(&options.help, "help", false, "Show this help message")
+	flag.BoolVar(&options.words, "w", false, "Concat or split standard input by words")
+
+	flag.Usage = func() {
+		fmt.Printf(`NAME:
+  dango - concat or split standard input
+
+USAGE:
+  dango [options]
+
+DESCRIPTION:
+  dango concat or split standard input.
+
+  e.g.
+    $ cat << EOF | dango -l -n 2
+    first
+    second
+    EOF
+    firstsecond
+
+    $ cat << EOF | dango -w
+    first second
+    EOF
+    first
+    second
+
+OPTIONS:
+`)
+		flag.PrintDefaults()
+	}
+}
+
+func (c *cli) run(args []string) int {
+	c.parseFlag(args)
+
+	if options.version {
+		_, _ = fmt.Fprintf(c.outStream, "dango version %s\n", version)
+		return 0
+	}
+	if options.help {
+		flag.Usage()
+		return 0
+	}
+
+	d := dango{
+		reader:    c.inStream,
+		writer:    c.outStream,
+		delimiter: []byte(options.delimiter),
+	}
+	err := d.run()
+	if err != nil {
+		msg := fmt.Sprintf("%+v\n", err)
+		_, _ = c.errStream.Write([]byte(msg))
+		return 1
+	}
+
+	return 0
+}
+
+func (c *cli) parseFlag(args []string) {
+	os.Args = args
+	options = dangoOptions{}
+	flag.Parse()
+}
diff --git a/cli_test.go b/cli_test.go
new file mode 100644
index 0000000..d0ed9c8
--- /dev/null
+++ b/cli_test.go
@@ -0,0 +1,105 @@
+package main
+
+import (
+	"bytes"
+	"strings"
+	"testing"
+)
+
+type param struct {
+	args     string
+	stdin    string
+	exitCode int
+	stdout   string
+	stderr   string
+}
+
+func TestSplitLines(t *testing.T) {
+	params := []param{
+		{args: "-l -n 1", stdin: "first\nsecond\n", exitCode: 0, stdout: "first\nsecond\n"},
+		{args: "-l -n 2", stdin: "first\nsecond\n", exitCode: 0, stdout: "firstsecond\n"},
+		{args: "-l -n 2", stdin: "first\n\nsecond\n", exitCode: 0, stdout: "first\nsecond\n"},
+		{args: "-l -n 2 -d _", stdin: "first\nsecond\n", exitCode: 0, stdout: "first_second\n"},
+		{args: "-l -n 3", stdin: "first\nsecond\nthird\n", exitCode: 0, stdout: "firstsecondthird\n"},
+		{args: "-l -n 3", stdin: "first\n\nsecond\n\nthird\n", exitCode: 0, stdout: "firstsecond\nthird\n"},
+	}
+
+	testRun(t, params)
+}
+
+func testRun(t *testing.T, params []param) {
+	for _, p := range params {
+		c, outStream, errStream := newCLI(p.stdin)
+		args := strings.Split(" "+p.args, " ")
+
+		exitCode := c.run(args)
+
+		if exitCode != p.exitCode {
+			t.Errorf("run(%s): Output = %q; want %q", args, exitCode, p.exitCode)
+		}
+		if outStream.String() != p.stdout {
+			t.Errorf("run(%s): Output = %q; want %q", args, outStream.String(), p.stdout)
+		}
+		if errStream.String() != p.stderr {
+			t.Errorf("run(%s): Err output = %q; want %q", args, errStream.String(), p.stderr)
+		}
+	}
+}
+
+func newCLI(stdin string) (c cli, outStream, errStream *bytes.Buffer) {
+	inStream := bytes.NewBufferString(stdin)
+	outStream = bytes.NewBuffer(nil)
+	errStream = bytes.NewBuffer(nil)
+	c = cli{inStream: inStream, outStream: outStream, errStream: errStream}
+	return
+}
+
+func TestSplitWords(t *testing.T) {
+	params := []param{
+		{args: "-w -n 1", stdin: "first\nsecond\n", exitCode: 0, stdout: "first\nsecond\n"},
+		{args: "-w -n 1", stdin: "first second\n", exitCode: 0, stdout: "first\nsecond\n"},
+		{args: "-w -n 2", stdin: "first\nsecond\n", exitCode: 0, stdout: "firstsecond\n"},
+		{args: "-w -n 2", stdin: "first\n\nsecond\n", exitCode: 0, stdout: "firstsecond\n"},
+		{args: "-w -n 2 -d _", stdin: "first\nsecond\n", exitCode: 0, stdout: "first_second\n"},
+		{args: "-w -n 3", stdin: "first\nsecond\nthird\n", exitCode: 0, stdout: "firstsecondthird\n"},
+		{args: "-w -n 3", stdin: "first\n\nsecond\n\nthird\n", exitCode: 0, stdout: "firstsecondthird\n"},
+	}
+
+	testRun(t, params)
+}
+
+func TestSplitCharacters(t *testing.T) {
+	params := []param{
+		{args: "-c -n 1", stdin: "12\n", exitCode: 0, stdout: "1\n2\n\n\n"},
+		{args: "-c -n 2", stdin: "1\n2\n", exitCode: 0, stdout: "1\n\n2\n\n"},
+		{args: "-c -n 2", stdin: "1234\n", exitCode: 0, stdout: "12\n34\n\n\n"},
+		{args: "-c -n 2", stdin: "12\n\n34\n", exitCode: 0, stdout: "12\n\n\n\n34\n\n\n"},
+		{args: "-c -n 2 -d _", stdin: "1234\n", exitCode: 0, stdout: "1_2\n3_4\n\n\n"},
+		{args: "-c -n 2", stdin: "１\n２\n", exitCode: 0, stdout: "１\n\n２\n\n"},
+		{args: "-c -n 3", stdin: "１\n２\n", exitCode: 0, stdout: "１\n２\n\n\n"},
+	}
+
+	testRun(t, params)
+}
+
+func TestSplitBytes(t *testing.T) {
+	params := []param{
+		{args: "-b -n 1", stdin: "12\n", exitCode: 0, stdout: "1\n2\n\n\n"},
+		{args: "-b -n 2", stdin: "12\n", exitCode: 0, stdout: "12\n\n\n"},
+		{args: "-b -n 2", stdin: "1\n2\n", exitCode: 0, stdout: "1\n\n2\n\n"},
+		{args: "-b -n 2", stdin: "1234\n", exitCode: 0, stdout: "12\n34\n\n\n"},
+		{args: "-b -n 2", stdin: "12\n\n34\n", exitCode: 0, stdout: "12\n\n\n\n34\n\n\n"},
+		{args: "-b -n 2 -d _", stdin: "1234\n", exitCode: 0, stdout: "1_2\n3_4\n\n\n"},
+	}
+
+	testRun(t, params)
+}
+
+func TestBufferSize(t *testing.T) {
+	params := []param{
+		{args: "-l -n 1 -B 1", stdin: "a\n", exitCode: 1, stdout: "", stderr: "failed to scan stdin: bufio.Scanner: token too long\n"},
+		{args: "-l -n 1 -B 2", stdin: "a\n", exitCode: 0, stdout: "a\n", stderr: ""},
+	}
+
+	testRun(t, params)
+}
diff --git a/dango.go b/dango.go
new file mode 100644
index 0000000..a6b654c
--- /dev/null
+++ b/dango.go
@@ -0,0 +1,113 @@
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"io"
+
+	"golang.org/x/xerrors"
+)
+
+const (
+	startBufSize = 4096 // Size of initial allocation for buffer.
+)
+
+type dango struct {
+	reader    io.Reader
+	writer    io.Writer
+	delimiter []byte
+}
+
+func (d *dango) run() error {
+	switch {
+	case options.bytes:
+		return d.splitBytes()
+	case options.lines:
+		return d.splitLines()
+	case options.words:
+		return d.splitWords()
+	case options.characters:
+		return d.splitCharacters()
+	default:
+		return d.splitLines()
+	}
+}
+
+func (d *dango) splitBytes() error {
+	return d.joinTokens(bufio.ScanBytes)
+}
+
+func (d *dango) splitWords() error {
+	return d.joinTokens(bufio.ScanWords)
+}
+
+func (d *dango) joinTokens(splitFunc bufio.SplitFunc) error {
+	scanner := bufio.NewScanner(d.reader)
+	scanner.Split(splitFunc)
+	if options.maxBufferSize > 0 {
+		size := startBufSize
+		if size > options.maxBufferSize {
+			size = options.maxBufferSize
+		}
+		b := make([]byte, size)
+		scanner.Buffer(b, options.maxBufferSize)
+	}
+
+	limit := options.size
+	count := 0
+	for scanner.Scan() {
+		t := scanner.Bytes()
+		count++
+
+		if err := d.addDelimiter(count, t); err != nil {
+			return fmt.Errorf("failed to add delimiter: %w", err)
+		}
+
+		_, err := d.writer.Write(t)
+		if err != nil {
+			return fmt.Errorf("failed to write to stdout: %w", err)
+		}
+		if limit > 0 && count >= limit {
+			_, err := d.writer.Write([]byte("\n"))
+			if err != nil {
+				return xerrors.Errorf("failed write LF: %w", err)
+			}
+			count = 0
+		}
+	}
+	if err := scanner.Err(); err != nil {
+		return fmt.Errorf("failed to scan stdin: %w", err)
+	}
+
+	if count != 0 && count != limit {
+		_, err := d.writer.Write([]byte("\n"))
+		if err != nil {
+			return xerrors.Errorf("failed write LF: %w", err)
+		}
+	}
+
+	return nil
+}
+
+func (d *dango) addDelimiter(count int, t []byte) error {
+	if count <= 1 {
+		return nil
+	}
+	if len(t) == 1 && t[0] == '\n' {
+		return nil
+	}
+
+	_, err := d.writer.Write(d.delimiter)
+	if err != nil {
+		return fmt.Errorf("failed to write delimiter to stdout: %w", err)
+	}
+	return nil
+}
+
+func (d *dango) splitLines() error {
+	return d.joinTokens(bufio.ScanLines)
+}
+
+func (d *dango) splitCharacters() error {
+	return d.joinTokens(bufio.ScanRunes)
+}
diff --git a/go.mod b/go.mod
new file mode 100644
index 0000000..9bb6242
--- /dev/null
+++ b/go.mod
@@ -0,0 +1,5 @@
+module github.com/ebc-2in2crc/dango
+
+go 1.15
+
+require golang.org/x/xerrors v0.0.0-20200804184101-5ec99f83aff1
diff --git a/go.sum b/go.sum
new file mode 100644
index 0000000..1ff365f
--- /dev/null
+++ b/go.sum
@@ -0,0 +1,2 @@
+golang.org/x/xerrors v0.0.0-20200804184101-5ec99f83aff1 h1:go1bK/D/BFZV2I8cIQd1NKEZ+0owSTG1fDTci4IqFcE=
+golang.org/x/xerrors v0.0.0-20200804184101-5ec99f83aff1/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
diff --git a/main.go b/main.go
new file mode 100644
index 0000000..772edd2
--- /dev/null
+++ b/main.go
@@ -0,0 +1,10 @@
+package main
+
+import "os"
+
+var version = "0.0.1"
+
+func main() {
+	c := cli{inStream: os.Stdin, outStream: os.Stdout, errStream: os.Stderr}
+	c.run(os.Args)
+}
diff --git a/todo.md b/todo.md
new file mode 100644
index 0000000..b19c98d
--- /dev/null
+++ b/todo.md
@@ -0,0 +1,14 @@
+# ToDo
+
+## やること
+
+- [x] `d.writer.Write([]byte("\n"))` とかのエラーをハンドルする
+- [ ] デバッグログを標準エラーに出すとか？ (オプションで)
+- [ ] CI をどうするか考える
+- [ ] リリースのやり方を考える。とりあえず Makefile でいつか GHA のが無難そう
+- [x] 英語の README を書く
+- [ ] バッジを README に配置する
+- [ ] Dockerfile を作る
+- [ ] ↑ README に書く
+- [ ] brew の Formula を書く
+- [ ] ↑を push する
\ No newline at end of file