Learn X By Example
Learn X By Example

    Go by Example: Exec'ing Processes

    Go by Example : Exec'ing Processes

    In the previous example we looked at spawning external processes . We do this when we need an external process accessible to a running Go process. Sometimes we just want to completely replace the current Go process with another (perhaps non-Go) one. To do this we’ll use Go’s implementation of the classic exec function.

    package main
    import (
    "os"
    "os/exec"
    "syscall"
)
    func main() {

    For our example we’ll exec ls . Go requires an absolute path to the binary we want to execute, so we’ll use exec.LookPath to find it (probably /bin/ls ).

        binary, lookErr := exec.LookPath("ls")
    if lookErr != nil {
        panic(lookErr)
    }

    Exec requires arguments in slice form (as opposed to one big string). We’ll give ls a few common arguments. Note that the first argument should be the program name.

        args := []string{"ls", "-a", "-l", "-h"}

    Exec also needs a set of environment variables to use. Here we just provide our current environment.

        env := os.Environ()

    Here’s the actual syscall.Exec call. If this call is successful, the execution of our process will end here and be replaced by the /bin/ls -a -l -h process. If there is an error we’ll get a return value.

        execErr := syscall.Exec(binary, args, env)
    if execErr != nil {
        panic(execErr)
    }
}

    When we run our program it is replaced by ls .

    $ go run execing-processes.go
total 16
drwxr-xr-x  4 mark 136B Oct 3 16:29 .
drwxr-xr-x 91 mark 3.0K Oct 3 12:50 ..
-rw-r--r--  1 mark 1.3K Oct 3 16:28 execing-processes.go

    Note that Go does not offer a classic Unix fork function. Usually this isn’t an issue though, since starting goroutines, spawning processes, and exec’ing processes covers most use cases for fork .

    Next example: Signals .

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