Added different usage options

Author: topscoder

README.md

@@ -1,6 +1,6 @@
-# ptr - Find hostname of IP addresses
+# IP PTR Lookup Script
 
--
+This is a simple Go script that performs PTR (reverse DNS) lookups for IP addresses. It can handle single IP addresses, IP addresses from a file, or IP addresses provided via stdin.
 
 ## Installation
 
@@ -11,3 +11,37 @@ go install github.com/topscoder/ptr@latest
 ```
 
 This will install the ptr script as an executable in your Go bin directory.
+
+## Usage
+
+Run the script with different options:
+
+* To look up a single IP address:
+
+```shell
+ptr 8.8.8.8
+```
+
+* To process IP addresses from a file (one IP address per line):
+
+```shell
+ptr ips.txt
+```
+
+* To provide IP addresses via stdin (press Ctrl + D to signal the end of input):
+
+```shell
+cat ips.txt | ptr -
+```
+
+Enjoy the PTR lookup results!
+
+## License
+
+This project is licensed under the MIT License.
+
+Feel free to fork the repository, make improvements, and submit pull requests!
+
+## Acknowledgements
+
+This script was inspired by the need for a simple tool to perform PTR lookups for multiple IP addresses quickly.

ptr.go

@@ -1,36 +1,151 @@
 package main
 
 import (
-    "fmt"
-    "net"
-    "os"
-    "strings"
+	"bufio"
+	"fmt"
+	"net"
+	"os"
+	"strings"
+	"sync"
 )
 
 func main() {
-    args := os.Args[1:]
+	args := os.Args[1:]
 
-    if len(args) != 1 {
-        fmt.Println("Usage: ptr <ip_address>")
-        return
-    }
+	if len(args) < 1 {
+		printUsage()
+		return
+	}
 
-    ip := args[0]
+	arg := args[0]
 
-    ptrDomainName, err := net.LookupAddr(ip)
-    if err != nil {
-        fmt.Println("No PTR record found for", ip)
-        return
-    }
+	if isFile(arg) {
+		processFile(arg)
+	} else if arg == "-" {
+		processStdin()
+	} else {
+		processSingleIP(arg)
+	}
+}
+
+func printUsage() {
+	fmt.Println("Usage:")
+	fmt.Println("  ptr <ip_address_or_input_file>")
+	fmt.Println()
+	fmt.Println("Options:")
+	fmt.Println("  <ip_address_or_input_file>  Provide an IP address, an input file with one IP address per line, or use '-' to read IP addresses from stdin.")
+}
+
+func isFile(path string) bool {
+	info, err := os.Stat(path)
+	if err != nil {
+		return false
+	}
+	return !info.IsDir()
+}
+
+func processFile(filePath string) {
+	file, err := os.Open(filePath)
+	if err != nil {
+		fmt.Println("Error opening file:", err)
+		return
+	}
+	defer file.Close()
+
+	scanner := bufio.NewScanner(file)
+	var wg sync.WaitGroup
+	ipChannel := make(chan string)
+
+	// Start worker goroutines
+	for i := 0; i < 10; i++ { // Adjust the number of goroutines as needed
+		wg.Add(1)
+		go processIPs(ipChannel, &wg)
+	}
+
+	// Send IPs to worker goroutines through channel
+	for scanner.Scan() {
+		ip := strings.TrimSpace(scanner.Text())
+		if ip != "" {
+			ipChannel <- ip
+		}
+	}
+	close(ipChannel)
+
+	wg.Wait()
+
+	if err := scanner.Err(); err != nil {
+		fmt.Println("Error reading file:", err)
+	}
+}
+
+func processStdin() {
+	scanner := bufio.NewScanner(os.Stdin)
+	var wg sync.WaitGroup
+	ipChannel := make(chan string)
+
+	// Start worker goroutines
+	for i := 0; i < 10; i++ { // Adjust the number of goroutines as needed
+		wg.Add(1)
+		go processIPs(ipChannel, &wg)
+	}
+
+	// Send IPs to worker goroutines through channel
+	for scanner.Scan() {
+		ip := strings.TrimSpace(scanner.Text())
+		if ip != "" {
+			ipChannel <- ip
+		}
+	}
+	close(ipChannel)
+
+	wg.Wait()
+
+	if err := scanner.Err(); err != nil {
+		fmt.Println("Error reading input:", err)
+	}
+}
+
+func processSingleIP(ip string) {
+	var wg sync.WaitGroup
+	ipChannel := make(chan string)
+
+	// Start worker goroutines
+	for i := 0; i < 10; i++ { // Adjust the number of goroutines as needed
+		wg.Add(1)
+		go processIPs(ipChannel, &wg)
+	}
+
+	// Send the single IP to worker goroutines through channel
+	ipChannel <- ip
+	close(ipChannel)
+
+	wg.Wait()
+}
+
+func processIPs(ipChannel <-chan string, wg *sync.WaitGroup) {
+	defer wg.Done()
+
+	for ip := range ipChannel {
+		ptrDomainNames, err := net.LookupAddr(ip)
+		if err != nil {
+			fmt.Printf("%s\t%v\n", ip, err)
+			continue
+		}
+
+		var cleanedDomainNames []string
+
+		for _, ptrDomainName := range ptrDomainNames {
+			// Remove the brackets from the PTR domain name.
+			ptrDomainName = strings.Trim(ptrDomainName, "[")
 
-    // Remove the brackets from the PTR domain name.
-    ptrDomainName = strings.Trim(ptrDomainName, "[")
-    ptrDomainName = strings.Trim(ptrDomainName, "]")
+			// Remove the last character if it is a dot.
+			if ptrDomainName[len(ptrDomainName)-1] == '.' {
+				ptrDomainName = ptrDomainName[:len(ptrDomainName)-1]
+			}
 
-    // Remove the last character if it is a dot.
-    if ptrDomainName[len(ptrDomainName)-1] == '.' {
-        ptrDomainName = ptrDomainName[:len(ptrDomainName)-1]
-    }
+			cleanedDomainNames = append(cleanedDomainNames, ptrDomainName)
+		}
 
-    fmt.Println(ptrDomainName)
+		fmt.Printf("%s\t%s\n", ip, strings.Join(cleanedDomainNames, "\n"))
+	}
 }