如何将exec.Command的输出传递到Golang中的另一个命令

Question

I have eight Microsoft access databases each one has around 215 tables and I needed to transfered those databases into postgresql so i used mdb-tools and exported the schemes which just one step ;but when it come to exporting tables data into postgres directly into postgresql i have to write this command for every single table:

mdb-export -I postgres -q \' myaccessdatabase.mdb table-name | psql -d mypsqldatabase -U postgres -w -h localhost 

so I have been trying to write a go command program to do as follows: 1. firstly excute a command to list tables name. which will be the arg of the next command. 2. then start for range looop to excute a command that export tanle data and the output of this command is pipe into the next command. 3. this command is psql which will write the output from the previous command ( which is sql insert statment)

package main

import (
    "bufio"
    "log"
    "os"
    "os/exec"
)
func main() {
    // command to Collect tables name and list it to the next command 
          tablesname := exec.Command("mdb-tables", "-1", "myaccessdatabase.mdb")

    // Run the command on each table name and get the output pipe/feed into the psql shell 
    for _, table := range tablesname {
        ls := exec.Command("mdb-export", "-I", "postgres", "-q", "\'", "myaccessdatabase.mdb", table)

        // | psql -d mydatabase -U postgres -w -h localhost command which will write each line from the output of previouse command's 
        visible := exec.Command("psql", "-d", "mypsqldatabase", "-U", "postgres", "-w", "-h", "localhost")



    }
}

So i have tried to pipe the output into the stdin of the next command and couldn't implement it , meanwhile I am trying with goroutin and channels just been unable to even come with a way to make this into the last command.

Thank you very much in advance.

Answer 1

The exec.Command function only creates the command, it doesn't execute it.

To get the output from tablesname := exec.Command("mdb-tables", "-1", "myaccessdatabase.mdb"), you need to run the command and capture its output:

tablesname := exec.Command("mdb-tables", "-1", "myaccessdatabase.mdb")
//capture the output pipe of the command
outputStream := bufio.NewScanner(tablesname.StdoutPipe())
tablesname.Start()  //Runs the command in the background

for outputStream.Scan() {   
//Default scanner is a line-by-line scan, so this will advance to the next line
    ls := exec.Command("mdb-export", "-I", "postgres", "-q", "\'", "myaccessdatabase.mdb", outputStream.Text())
    ls.Run()  //Blocks until command finishes execution

    visible := exec.Command("psql", "-d", "mypsqldatabase", "-U", "postgres", "-w", "-h", "localhost")
    visible.Run()
}

tablesname.Wait()  //Cleanup 

BEWARE: For database interactions, exec isn't idiomatic code.

The SQL library allows direct interaction with the database: http://golang.org/pkg/database/sql/