How can I source a shell script using Go? - bash

Question

I want to source shell scripts using Go. Ideally the following code
cmd := exec.Command("/bin/bash", "source", file.Name())
but, I know that "source" is a bash built-in function, not an executable.
However, I have found some ways to mimic this behavior in Python:
http://pythonwise.blogspot.fr/2010/04/sourcing-shell-script.html
Unfortunately, I don't know how to translate this in Go. Does anyone have an idea ?
Thanks !

Answer 1

You can set environmental variables when running a program using exec:
cmd := exec.Command("whatever")
cmd.Env = []string{"A=B"}
cmd.Run()
If you really need source then you can run your command through bash:
cmd := exec.Command("bash", "-c", "source " + file.Name() + " ; echo 'hi'")
cmd.Run()
Check out this library for a more full-featured workflow: https://github.com/progrium/go-basher.
Update: Here's an example that modifies the current environment:
package main
import (
"bufio"
"bytes"
"io/ioutil"
"log"
"os"
"os/exec"
"strings"
)
func main() {
err := ioutil.WriteFile("example_source", []byte("export FOO=bar; echo $FOO"), 0777)
if err != nil {
log.Fatal(err)
}
cmd := exec.Command("bash", "-c", "source example_source ; echo '<<<ENVIRONMENT>>>' ; env")
bs, err := cmd.CombinedOutput()
if err != nil {
log.Fatalln(err)
}
s := bufio.NewScanner(bytes.NewReader(bs))
start := false
for s.Scan() {
if s.Text() == "<<<ENVIRONMENT>>>" {
start = true
} else if start {
kv := strings.SplitN(s.Text(), "=", 2)
if len(kv) == 2 {
os.Setenv(kv[0], kv[1])
}
}
}
}
log.Println(os.Getenv("FOO"))

Answer 2

I have recently added such a utility function to my shell/bash Golang library:
https://godoc.org/mvdan.cc/sh/shell#SourceFile
For example, you could do:
vars, err := shell.SourceFile("foo.sh")
if err != nil { ... }
fmt.Println(vars["URL"].Value)
// http://the.url/value
It's decently safe, because it never actually calls bash nor any other program. It parses the shell script, then interprets it. But when interpreting, it has a whitelist of what files the script can open and what programs the script can execute.
The interpreter also has a context.Context, so you can set a timeout if you want to be protected against forever loops or other bad code.