file-finder.go

// Resource: https://zetcode.com/golang/find-file/ 
package main

import (
    "fmt"
    "log"
    "os"
    "path/filepath"
    "regexp"
)

var files []string

func VisitFile(path string, info os.FileInfo, err error) error {

    if err != nil {

        fmt.Println(err)
        return nil
    }

    if info.IsDir() || filepath.Ext(path) != ".txt" {

        return nil
    }

    reg, err2 := regexp.Compile("^[la]")

    if err2 != nil {

        return err2
    }

    if reg.MatchString(info.Name()) {

        files = append(files, path)
    }

    return nil
}

func main() {

    err := filepath.Walk("some/folder", VisitFile)

    if err != nil {

        log.Fatal(err)
    }

    for _, file := range files {

        fmt.Println(file)
    }
}