Emulate Perl's diamond operator in Go.

diamond.go

package main

import (
	"bufio"
	"fmt"
	"os"
)

func main() {

	filenames := []string{"-"}

	if len(os.Args) > 1 {
		filenames = os.Args[1:]
	}

	totalLineCount := 0

	for _, filename := range filenames {

		var file *os.File
		var err error

		if filename == "-" {
			file = os.Stdin
		} else {
			if file, err = os.Open(filename); err != nil {
				fmt.Fprintln(os.Stderr, err)
				continue
			}
			defer file.Close()
		}

		fileLineCount := 0

		scanner := bufio.NewScanner(file)
		for scanner.Scan() {
			fileLineCount++
			totalLineCount++

			line := scanner.Text()

			// do something with line here

			fmt.Printf("%d (%d): %s\n", fileLineCount, totalLineCount, line)
		}
		if err := scanner.Err(); err != nil {
			fmt.Fprintln(os.Stderr, err)
			continue
		}
	}
}

Perl is also keeping track of the line number in $. automatically; we'd have to do that ourselves if we cared. But it doesn't reset for the next file, so it would be like totalLineCount rather than fileLineCount.