141 lines
3.9 KiB
Go
141 lines
3.9 KiB
Go
package main
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import (
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"bufio"
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"flag"
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"fmt"
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"log"
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"os"
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"regexp"
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"strconv"
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"strings"
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)
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func printUsage() {
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fmt.Fprintf(os.Stderr, "Usage: %s [options] <range specification> [file]\n", os.Args[0])
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fmt.Fprintln(os.Stderr, "Options:")
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flag.PrintDefaults()
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fmt.Fprintln(os.Stderr, "\nRange specification examples:")
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fmt.Fprintln(os.Stderr, "10,20 Reads lines 10 to 20 from the input")
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fmt.Fprintln(os.Stderr, "15:+5 Reads 5 lines starting from line 15")
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fmt.Fprintln(os.Stderr, "3 Reads from line 3 to the end of the file")
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fmt.Fprintln(os.Stderr, "+2 Reads the first 2 lines")
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fmt.Fprintln(os.Stderr, "Please ensure you input valid range specifications and file paths.")
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os.Exit(1)
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}
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func parseArgs(args []string) (int, int, string, error) {
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var filename string
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var start, length, end int
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found := false
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// Concatenate all arguments to a single string for easier parsing
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joinedArgs := strings.Join(args, " ")
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// Regular expression to match ranges and numbers
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rangeRegex := regexp.MustCompile(`((\d+)?([ :,;-]))(\+)?(\d+)`)
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range2Regex := regexp.MustCompile(`((\d+)([ :,;-]))`)
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range3Regex := regexp.MustCompile(`(\+)?(\d+)`)
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matches := rangeRegex.FindStringSubmatch(joinedArgs)
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if matches != nil {
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//check if start was defined
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if matches[2] != "" {
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start, _ = strconv.Atoi(matches[2]) // Convert start line to integer
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} else {
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start = 1
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}
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if matches[4] == "+" { // Check if it's a relative length
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length, _ = strconv.Atoi(matches[5]) // Convert length to integer
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end = start + length - 1
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} else {
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end, _ = strconv.Atoi(matches[5]) // Convert end line to integer
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}
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// Remove the matched part from the arguments
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joinedArgs = strings.Replace(joinedArgs, matches[0], "", 1)
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found = true
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} else {
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matches = range2Regex.FindStringSubmatch(joinedArgs)
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if matches != nil {
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start, _ = strconv.Atoi(matches[2]) // Convert start line to integer
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end = -1
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// Remove the matched part from the arguments
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joinedArgs = strings.Replace(joinedArgs, matches[0], "", 1)
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found = true
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} else {
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matches = range3Regex.FindStringSubmatch(joinedArgs)
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if matches != nil {
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if matches[1] == "+" { // Check if it's a relative length
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length, _ := strconv.Atoi(matches[2]) // Convert length to integer
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start = 1
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end = start + length - 1
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} else { // Otherwise convert it to an absolute length
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start, _ = strconv.Atoi(matches[2]) // Convert start line to integer
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end = -1
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// Remove the matched part from the arguments
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}
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joinedArgs = strings.Replace(joinedArgs, matches[0], "", 1)
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found = true
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} else {
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found = false
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printUsage()
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}
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}
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}
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// Clean up and identify the filename, if present
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joinedArgs = strings.TrimSpace(joinedArgs)
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if joinedArgs != "" && !found {
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// If we didn't find numbers, interpret the remaining as filename
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filename = joinedArgs
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} else if joinedArgs != "" {
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// Otherwise, interpret any non-empty remaining part as filename
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filename = joinedArgs
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}
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if !found {
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return 0, 0, "", fmt.Errorf("no valid range or line number found")
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}
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return start, end, filename, nil
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}
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func main() {
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flag.Parse()
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args := flag.Args()
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if len(args) < 1 {
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printUsage()
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os.Exit(1)
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}
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startIndex, endIndex, filename, err := parseArgs(args)
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if err != nil {
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fmt.Fprintf(os.Stderr, "Error parsing arguments: %v\n", err)
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os.Exit(1)
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}
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// Detemine the input source (file or stdin)
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inputSource := os.Stdin
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if filename != "" {
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inputSource, err = os.Open(filename)
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if err != nil {
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log.Fatalf("Failed to open file: %v\n", err)
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}
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defer inputSource.Close()
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}
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scanner := bufio.NewScanner(inputSource)
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//print all lines from line buner start to linenumber end unless linenumber end is -1
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for i := 1; scanner.Scan(); i++ {
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if startIndex <= i && (i <= endIndex || endIndex == -1) {
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fmt.Println(scanner.Text())
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}
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}
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if err := scanner.Err(); err != nil {
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log.Fatal(err)
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}
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}
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