54 lines
1.4 KiB
Go
54 lines
1.4 KiB
Go
// ## Line Filters
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// A line filter program reads input on stdin,
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// processes it, and prints results to stdout.
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// Here's an example line filter that writes
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// a capitalized version of all text it reads.
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package main
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// Package `bufio` will help us read line-by-line.
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import "bufio"
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import "bytes"
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import "os"
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import "io"
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// We'll need to add our own newlines between
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// processed lines.
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func main() {
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newline := []byte("\n")
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// The buffered reader gives us `ReadLine`.
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in := bufio.NewReader(os.Stdin)
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out := os.Stdout
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// If successful, each `ReadLine` returns bytes and a
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// boolean indicating if don't have the whole line yet.
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for {
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inBytes, pfx, err := in.ReadLine()
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// The `EOF` error is expected when we reach the end
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// of the input, so exit gracefully in that case.
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// Otherwise there is a problem.
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if err == io.EOF {
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return
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}
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if err != nil {
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panic(err)
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}
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// Write out the upercased bytes, checking for an error
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// here as well.
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outBytes := bytes.ToUpper(inBytes)
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_, err = out.Write(outBytes)
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if err != nil {
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panic(err)
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}
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// Unless this read was for a prefix (not the full
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// line), we need to add our own newline.
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if !pfx {
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out.Write(newline)
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}
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}
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}
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