50 lines
2.1 KiB
Go
50 lines
2.1 KiB
Go
package main // A line-filter program reads input on stdin,
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// processes it, and prints results to stdout.
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// Here is an example line filter that writes a
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// a captialized version of all text it reads.
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import "bufio" // Package `bufio` will help us read line-by-line.
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import "bytes"
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import "os"
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import "io"
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func main() {
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newline := []byte("\n") // We'll need to add our own newlines
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// between processed lines.
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in := bufio.NewReader(os.Stdin) // The buffered reader gives us `ReadLine`.
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out := os.Stdout
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for { // If succesful, each `ReadLine` returns bytes and a
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inBytes, pfx, err := in.ReadLine() // boolean indicating if don't have the whole line.
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if err == io.EOF { // The `EOF` error is expected when we reach the end
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return // of the input, so exit gracefully in that case.
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} // Otherwise there is a problem.
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if err != nil {
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panic (err)
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}
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outBytes := bytes.ToUpper(inBytes) // `bytes.ToUpper` works directly on bytes, so we don't
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// need to convert to a string for `strings.ToUpper`.
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_, err = out.Write(outBytes) // Write out the upercased bytes, checking for an error
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if err != nil { // here as well.
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panic(err)
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}
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if !pfx { // Unless this read was for a prefix (not the full
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out.Write(newline) // line), we need to add our own newline.
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}
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}
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}
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/*
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$ cat > lines // Make a file with a few lowercase lines.
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hello
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filter
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$ cat lines | go run line-filter.go // Use the line filter to get upercase lines.
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HELLO
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FILTER
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*/
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