Go by Example: Line Filters

Go by Example : Line Filters

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.
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)`
`Text`returns the current token, here the next line, from the input.	`for scanner.Scan() {`
	`ucl := strings.ToUpper(scanner.Text())`
Write out the uppercased line.	`fmt.Println(ucl) }`
Check for errors during `Scan`. End of file is expected and not reported by `Scan`as an error.	`if err := scanner.Err(); err != nil { fmt.Fprintln(os.Stderr, "error:", err) os.Exit(1) } }`

To try out our line filter, first make a file with a few lowercase lines.	`$ echo 'hello' > /tmp/lines $ echo 'filter' >> /tmp/lines`
Then use the line filter to get uppercase lines.	`$ cat /tmp/lines \| go run line-filters.go HELLO FILTER`

Next example: File Paths .