How to redirect stdout from docker container to ho

问题:

I'm trying to call docker's mysqldump from host system for save mysql dump from golang. It works correctly with host mysqldump, but don't work with docker's mysqldump.

func writeDb(dbName string)
{
   var mysqldumpPath string = "/usr/bin/mysqldump"
 //var mysqldumpPath string = "/Applications/MAMP/Library/bin/mysqldump"

 //cmd := exec.Command(mysqldumpPath, fmt.Sprintf("-u%s", USER), fmt.Sprintf("-p%s", PASSWORD) , dbName)
   cmd := exec.Command("docker", "exec", "some-mysql", mysqldumpPath, fmt.Sprintf("%s", USER), fmt.Sprintf("-p%s", PASSWORD) , dbName, ">", fmt.Sprintf("%s.sql", dbName))

   stdout, err := cmd.StdoutPipe()
   if err != nil
   {
     log.Fatal(err)
   }

   if err := cmd.Start(); err != nil
   {
     log.Fatal(err)
   }

   bytes, err := ioutil.ReadAll(stdout)
   if err != nil
   {
      log.Fatal(err)
   }
   err = ioutil.WriteFile("./backup/" + dbName +".sql", bytes, 0644)
   if err != nil
   {
     panic(err)
   }

}

I got only that for non-empty database empty mysql dump

回答1:

Instead of mysql, try a simple command like :

• pwd
• echo a > b, just to see if you do see a file b on your host.

You need to make that redirection inside the container in a folder which has been mounted from the host (using volume), in order for the created file to persists, once docker exec exits the container.

回答2:

The solution is:

func writeDb(dbName string) {
var mysqldumpPath string = "/usr/bin/mysqldump"
cmd := exec.Command("docker", "exec", "some-mysql", mysqldumpPath, "-u", fmt.Sprintf("%s", USER), fmt.Sprintf("-p%s", PASSWORD) , fmt.Sprintf("%s", dbName))

stdout, err := cmd.StdoutPipe()
if err != nil {
    log.Fatal(err)
}

if err := cmd.Start(); err != nil {
    log.Fatal(err)
}

bytes, err := ioutil.ReadAll(stdout)
if err != nil {
    log.Fatal(err)
}
err = ioutil.WriteFile("./backup/" + dbName +".sql", bytes, 0644)
if err != nil {
    panic(err)
}

}

Just without "> dbname.sql"

回答3:

EDIT:

The OP doesn't work inside go code. It gives an error: the input device is not a TTY. I will try to find out why and update the post...

---

OP:

What about using docker exec -it [command]

Example:

# start a new mysql container...
$ docker run --rm -d --name="test_mysql" -e MYSQL_ROOT_PASSWORD=root mysql

# mysqldump > stdout
$ docker exec -it test_mysql mysqldump -u root -proot sys

or

# mysqldump > stdout > file
$ docker exec -it test_mysql mysqldump -u root -proot sys > sys.sql