Skip to content

Line filters

Context

Line filters read input line by line (from stdin or a file) and transform each line. Common in Unix pipelines. Use bufio.Scanner to read lines.

Example

A filter that converts each line to uppercase.

Code example

package main

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

func main() {
    scanner := bufio.NewScanner(os.Stdin)
    for scanner.Scan() {
        line := scanner.Text()
        fmt.Println(strings.ToUpper(line))
    }
    if err := scanner.Err(); err != nil {
        fmt.Fprintln(os.Stderr, "error:", err)
        os.Exit(1)
    }
}

Output (if input is “hello\nworld”)

HELLO
WORLD

Useful links