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