Stdin Line Filter

Post Example

A line filter is a common type of program that reads input on stdin, processes it, and then prints some derived result to stdout. grep and sed are common line filters.

Examples in Go

Stdin Line Filter in Go

by yhuang Go bufio bufio.NewScanner fmt fmt.Fprintln fmt.Println

Here’s an example line filter in Go that writes a capitalized version of all input text. You can use this pattern to write your own Go line filters.

package main

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

func main() {

    // Wrapping the unbuffered os.Stdin with a buffered scanner gives us a convenient
    // Scan method that advances the scanner to the next token;
    // which is the next line in the default scanner.
    scanner := bufio.NewScanner(os.Stdin)

    for scanner.Scan() {

        ucl := strings.ToUpper(scanner.Text())
        // Write out the uppercased line.
        fmt.Println(ucl)
    }

    if err := scanner.Err(); err != nil {
        fmt.Fprintln(os.Stderr, "error:", err)
        os.Exit(1)
    }
}