45: grep

This exercise is pending. Quick notes about this exercise:

• My implemention is at https://lcthw.dev/go/go-coreutils
• https://www.gnu.org/software/grep/manual/html_node/index.html
• os -- https://pkg.go.dev/os@go1.25.3
• path -- probably all of them use it
• regex -- https://pkg.go.dev/regexp@go1.25.3
• slices -- https://pkg.go.dev/slices@go1.25.3
• strings -- https://pkg.go.dev/strings@go1.25.3

The Code

View Source file go-coreutils/grep/main.go Only

package main

import (
  "fmt"
  "regexp"
  "os"
  "bufio"
  "flag"
  "log"
  "io"
)

func ScanInput(input io.Reader, exp string, prefix string) {
    scan := bufio.NewScanner(input)
    re, err := regexp.Compile(exp)

    if err != nil { log.Fatal(err) }

    for scan.Scan() {
        line := scan.Text()

        if re.MatchString(line) {
            if prefix != "" {
                fmt.Print(prefix, ": ")
            }

            fmt.Println(line)
        }
    }
}

func main() {
    flag.Parse()

    args := flag.Args()

    if len(args) == 0 {
        log.Fatal("USAGE: grep <regex> [files...]")
    } else if len(args) == 1 {
        ScanInput(os.Stdin, args[0], "")
    } else {
        exp := args[0]
        files := args[1:]

        for _, file := range files {
            input, err := os.Open(file)
            if err != nil { log.Fatal(err) }

            ScanInput(input, exp, file)
        }
    }
}