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74 lines
2.3 KiB
Go
74 lines
2.3 KiB
Go
// Sometimes our Go programs need to spawn other, non-Go
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// processes. For example, the syntax highlighting on this
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// site is [implemented](https://github.com/mmcgrana/gobyexample/blob/master/tools/generate.go)
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// by spawning a [`pygmentize`](http://pygments.org/)
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// process from a Go program. Let's look at a few examples
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// of spawning processes from Go.
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package main
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import (
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"fmt"
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"io/ioutil"
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"os/exec"
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)
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func main() {
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// We'll start with a simple command that takes no
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// arguments or input and just prints something to
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// stdout. The `exec.Command` helper creates an object
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// to represent this external process.
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dateCmd := exec.Command("date")
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// `.Output` is another helper that handles the common
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// case of running a command, waiting for it to finish,
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// and collecting its output. If there were no errors,
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// `dateOut` will hold bytes with the date info.
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dateOut, err := dateCmd.Output()
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if err != nil {
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panic(err)
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}
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fmt.Println("> date")
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fmt.Println(string(dateOut))
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// Next we'll look at a slightly more involved case
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// where we pipe data to the external process on its
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// `stdin` and collect the results from its `stdout`.
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grepCmd := exec.Command("grep", "hello")
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// Here we explicitly grab input/output pipes, start
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// the process, write some input to it, read the
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// resulting output, and finally wait for the process
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// to exit.
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grepIn, _ := grepCmd.StdinPipe()
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grepOut, _ := grepCmd.StdoutPipe()
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grepCmd.Start()
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grepIn.Write([]byte("hello grep\ngoodbye grep"))
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grepIn.Close()
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grepBytes, _ := ioutil.ReadAll(grepOut)
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grepCmd.Wait()
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// We ommited error checks in the above example, but
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// you could use the usual `if err != nil` pattern for
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// all of them. We also only collect the `StdoutPipe`
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// results, but you could collect the `StderrPipe` in
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// exactly the same way.
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fmt.Println("> grep hello")
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fmt.Println(string(grepBytes))
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// Note that when spawning commands we need to
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// provide an explicitly delineated command and
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// argument array, vs. being able to just pass in one
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// command-line string. If you want to spawn a full
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// command with a string, you can use `bash`'s `-c`
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// option:
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lsCmd := exec.Command("bash", "-c", "ls -a -l -h")
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lsOut, err := lsCmd.Output()
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if err != nil {
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panic(err)
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}
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fmt.Println("> ls -a -l -h")
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fmt.Println(string(lsOut))
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}
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