How to Execute Piped Commands in Go using exec.Command()?

Executing Commands with Pipes in Go Using exec.Command()

When working with the exec.Command() function in Go, users may encounter difficulties when attempting to execute commands that involve pipes. While executing simple commands is straightforward, using pipes within those commands can pose challenges.

Problem:

In this instance, users have observed that while the following command executes successfully and prints the output of the "ps" command:

out, err := exec.Command("ps", "cax").Output()

Attempting to use a pipe within the command, as seen below, results in an error:

out, err := exec.Command("ps", "cax | grep myapp").Output()

Solution:

To address this issue, there are two approaches to consider:

1. Passing Everything to Bash:

One option is to pass the entire command line to bash and have it execute the pipeline for you. This approach can be achieved by using the following code:

out, err := exec.Command("bash", "-c", "ps cax | grep myapp").Output()

2. More Idiomatic Approach:

A more idiomatic way of handling this situation is to use the exec.Command() function to create two separate commands and then connect their input and output streams. This can be accomplished as follows:

package main

import (
    "fmt"
    "os/exec"
)

func main() {
    grep := exec.Command("grep", "redis")
    ps := exec.Command("ps", "cax")

    // Get ps's stdout and attach it to grep's stdin.
    pipe, _ := ps.StdoutPipe()
    defer pipe.Close()

    grep.Stdin = pipe

    // Run ps first.
    ps.Start()

    // Run and get the output of grep.
    res, _ := grep.Output()

    fmt.Println(string(res))
}

In this example, the "ps" command is executed first, and its output is piped into the "grep" command, which filters the output based on the "redis" string. The result is then printed to the standard output.

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