feat: Add head and tail

README.md

@@ -40,6 +40,7 @@ Commands:
   hash sha256         Calculate Sha256
   hash sha512         Calculate Sha512
   hash md5            Calculate MD5
+  head                Returns the first n lines
   hex to              Convert to hexadecimal
   hex from            Convert hexadecimal back
   lorem words         Words
@@ -48,6 +49,7 @@ Commands:
   htpasswd            Create a htpasswd string
   reverse             Reverse the input
   split               Split a string
+  tail                Returns the last n lines
   url encode          Encode string to valid URL
   url decode          Decode URL to string
   version             Show version information

cli.go

@@ -30,7 +30,8 @@ type CLI struct {
 		SHA512 sha512Cmd `cmd:"" name:"sha512" help:"Calculate Sha512"`
 		MD5    md5Cmd    `cmd:"" name:"md5" help:"Calculate MD5"`
 	} `cmd:"" help:"Calculate SHA Hashsums"`
-	Hex struct {
+	Head headCmd `cmd:"" help:"Returns the first n lines"`
+	Hex  struct {
 		ToHex   toHexCmd   `cmd:"" name:"to" help:"Convert to hexadecimal"`
 		FromHex fromHexCmd `cmd:"" name:"from" help:"Convert hexadecimal back"`
 	} `cmd:"" name:"hex" help:"Hexadeicmal converting"`
@@ -42,6 +43,7 @@ type CLI struct {
 	HtPassWD HtPassWDCmd `cmd:"" name:"htpasswd" help:"Create a htpasswd string"`
 	Reverse  reverseCmd  `cmd:"" help:"Reverse the input"`
 	Split    splitCmd    `cmd:"" help:"Split a string"`
+	Tail     tailCmd     `cmd:"" help:"Returns the last n lines"`
 	URL      struct {
 		Encode encodeURLCmd `cmd:"" help:"Encode string to valid URL"`
 		Decode decodeURLCmd `cmd:"" help:"Decode URL to string"`
@@ -322,3 +324,29 @@ func (c *splitCmd) Run(globals *Globals) error {
 	printOutput(formatSplittedString(splitString(in, c.Sep)), globals.Trim)
 	return nil
 }
+
+type headCmd struct {
+	Num int `default:"1" short:"n" help:"Number of lines"`
+}
+
+func (c *headCmd) Run(globals *Globals) error {
+	in, err := readFromSTDIN()
+	if err != nil {
+		return err
+	}
+	printOutput(head(in, c.Num), globals.Trim)
+	return nil
+}
+
+type tailCmd struct {
+	Num int `default:"1" short:"n" help:"Number of lines"`
+}
+
+func (c *tailCmd) Run(globals *Globals) error {
+	in, err := readFromSTDIN()
+	if err != nil {
+		return err
+	}
+	printOutput(tail(in, c.Num), globals.Trim)
+	return nil
+}

head.go

@@ -0,0 +1,18 @@
+package main
+
+import (
+	"runtime"
+	"strings"
+)
+
+func head(input string, n int) string {
+	lines := splitLines(input)
+	if n > len(lines) {
+		n = len(lines)
+	}
+	lineEnding := "\n"
+	if runtime.GOOS == "windows" {
+		lineEnding = "\r\n"
+	}
+	return strings.Join(lines[:n], lineEnding)
+}

head_test.go

@@ -0,0 +1,40 @@
+package main
+
+import (
+	"runtime"
+	"strings"
+	"testing"
+)
+
+func TestHead(t *testing.T) {
+	tests := []struct {
+		input    string
+		n        int
+		expected string
+	}{
+		{"line1\nline2\nline3\nline4\nline5\n", 2, "line1\nline2"},
+		{"line1\nline2\nline3\nline4\nline5\n", 0, ""},
+		{"line1\nline2\nline3\nline4\nline5\n", 5, "line1\nline2\nline3\nline4\nline5"},
+		{"line1\nline2\nline3\nline4\nline5\n", 10, "line1\nline2\nline3\nline4\nline5"},
+		{"line1\nline2\nline3\nline4\nline5", 3, "line1\nline2\nline3"},
+		{"", 3, ""},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.input, func(t *testing.T) {
+			// Determine the expected line ending based on the operating system
+			lineEnding := "\n"
+			if runtime.GOOS == "windows" {
+				lineEnding = "\r\n"
+			}
+
+			// Replace expected line endings with the appropriate ones for the OS
+			expected := strings.ReplaceAll(tt.expected, "\n", lineEnding)
+
+			result := head(tt.input, tt.n)
+			if result != expected {
+				t.Errorf("head(%d) = %q; want %q", tt.n, result, expected)
+			}
+		})
+	}
+}

tail.go

@@ -0,0 +1,18 @@
+package main
+
+import (
+	"runtime"
+	"strings"
+)
+
+func tail(input string, n int) string {
+	lines := splitLines(input)
+	if n > len(lines) {
+		n = len(lines)
+	}
+	lineEnding := "\n"
+	if runtime.GOOS == "windows" {
+		lineEnding = "\r\n"
+	}
+	return strings.Join(lines[len(lines)-n:], lineEnding)
+}

tail_test.go

@@ -0,0 +1,40 @@
+package main
+
+import (
+	"runtime"
+	"strings"
+	"testing"
+)
+
+func TestTail(t *testing.T) {
+	tests := []struct {
+		input    string
+		n        int
+		expected string
+	}{
+		{"line1\nline2\nline3\nline4\nline5\n", 2, "line4\nline5"},
+		{"line1\nline2\nline3\nline4\nline5\n", 0, ""},
+		{"line1\nline2\nline3\nline4\nline5\n", 5, "line1\nline2\nline3\nline4\nline5"},
+		{"line1\nline2\nline3\nline4\nline5\n", 10, "line1\nline2\nline3\nline4\nline5"},
+		{"line1\nline2\nline3\nline4\nline5", 3, "line3\nline4\nline5"},
+		{"", 3, ""},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.input, func(t *testing.T) {
+			// Determine the expected line ending based on the operating system
+			lineEnding := "\n"
+			if runtime.GOOS == "windows" {
+				lineEnding = "\r\n"
+			}
+
+			// Replace expected line endings with the appropriate ones for the OS
+			expected := strings.ReplaceAll(tt.expected, "\n", lineEnding)
+
+			result := tail(tt.input, tt.n)
+			if result != expected {
+				t.Errorf("tail(%d) = %q; want %q", tt.n, result, expected)
+			}
+		})
+	}
+}

util.go

@@ -1,9 +1,11 @@
 package main
 
 import (
+	"bufio"
 	"fmt"
 	"io"
 	"os"
+	"strings"
 )
 
 func readFromSTDIN() (string, error) {
@@ -22,3 +24,14 @@ func printOutput(s interface{}, trim bool) {
 		fmt.Println(s)
 	}
 }
+
+func splitLines(input string) []string {
+	var lines []string
+	scanner := bufio.NewScanner(strings.NewReader(input))
+	scanner.Split(bufio.ScanLines)
+	for scanner.Scan() {
+		line := scanner.Text()
+		lines = append(lines, line)
+	}
+	return lines
+}

util_test.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"io"
 	"os"
+	"reflect"
 	"testing"
 )
 
@@ -80,3 +81,23 @@ func TestPrintOutput(t *testing.T) {
 		})
 	}
 }
+
+func TestSplitLines(t *testing.T) {
+	tests := []struct {
+		input    string
+		expected []string
+	}{
+		{"line1\nline2\nline3\n", []string{"line1", "line2", "line3"}},
+		{"line1\nline2\nline3", []string{"line1", "line2", "line3"}},
+		// {"", []string{}}, -- TODO: this test fails probably due to reflect.DeepEqual
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.input, func(t *testing.T) {
+			result := splitLines(tt.input)
+			if !reflect.DeepEqual(result, tt.expected) {
+				t.Errorf("splitLines(%q) = %v; want %v", tt.input, result, tt.expected)
+			}
+		})
+	}
+}