How to Properly Pipe Commands in Go\'s `os/exec` Package?

Piping Commands in Go Using Exec Package

Piping commands in Go can be achieved using the os/exec package. However, when attempting to pipe the output of one command into another, difficulties might arise. This article addresses such challenges and provides a solution.

Consider the following command that pipes the stdout from phantomjs into ffmpeg to create a video from captured images:

phantomjs runner.js | ffmpeg -y -c:v png -f image2pipe -r 25 -t 10  -i - -c:v libx264 -pix_fmt yuv420p -movflags +faststart dragon.mp4

Issue:

Executing this command with exec.Command(parts[0], parts[1:]...), where parts represents the command components, does not honor the pipe.

Solution:

To effectively pipe the output, employ the following approach:

Use exec.Command("bash", "-c", command) to execute the command as a bash script, where command is the desired piped command. This method handles pipes transparently.

Example:

import (
    "fmt"
    "os/exec"
)

func main() {
    cmd := "phantomjs runner.js | ffmpeg -y -c:v png -f image2pipe -r 25 -t 10  -i - -c:v libx264 -pix_fmt yuv420p -movflags +faststart dragon.mp4"
    output, err := exec.Command("bash", "-c", cmd).Output()
    if err != nil {
        fmt.Printf("Failed to execute command: %s", cmd)
    }
    fmt.Println(string(output))
}

By executing the command as a bash script, the pipe is now honored, allowing the output of phantomjs to be seamlessly fed into ffmpeg.

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