I'm currently trying to execute a simple echo command in Golang on Linux. My code is the following:
cmd = exec.Command("echo", "\"foo 0x50\"", ">", "test.txt")
_, err = cmd.Output()
if err != nil {
fmt.Println(err)
}
But test.txt doesn't appear in my folder (even after compile and run the code). That not the first that that I use this method to execute commands and I never thought that I will be block on an echo command.
So how can I fix this code in order to have "foo 0x50" (with the quotes) in the test.txt?
You can redirect the stdout like this:
// Remove the redirect from command
cmd := exec.Command("echo", "\"foo 0x50\"")
// Make test file
testFile, err := os.Create("test.txt")
if err != nil {
panic(err)
}
defer outfile.Close()
// Redirect the output here (this is the key part)
cmd.Stdout = testFile
err = cmd.Start(); if err != nil {
panic(err)
}
cmd.Wait()
For anyone who wants to pass the complete command in oneline/string ,
func call(command string) {
cmd := exec.Command("sudo", "bash", "-c", command)
cmd.Stdin = os.Stdin
cmd.Stdout = os.Stdout
cmd.Stderr = os.Stderr
err := cmd.Start()
if err != nil {
fmt.Println(err)
}
err1 := cmd.Wait()
if err1 != nil {
fmt.Println(err1)
}
}
The Wait waits for the command to exit and waits for any copying to stdin or copying from stdout or stderr to complete. It closes the pipe after seeing the command exit.
Sources :
https://stackoverflow.com/a/43246464/9892358
https://stackoverflow.com/a/43246464/9892358
https://zetcode.com/golang/exec-command/
Related
I've been trying to write a program that record what is passed to a subprocess and the console returns in live (in the future, to record SSH sessions, for now on Python shell for testing)
I can record without issue stdout and stderr (it shows and record it correctly) but I can't find a way to do the same on stdin ?
Basically that my stdin will both map to the subprocess stdin and write to the log file.
There is my current code :
func SSH(cmd *cobra.Command, args []string) {
logFile := fmt.Sprintf("%v#%s.log", args[0], time.Now().Format(SSHLogDateFormat))
usr, _ := user.Current()
home := usr.HomeDir
logDir := fmt.Sprintf("%s/%s/logs", home, config.ConfigDir)
if _, err := os.Stat(logDir); os.IsNotExist(err) {
err = os.Mkdir(logDir, os.FileMode(int(0700)))
if err != nil {
log.Fatalf("Failed to create %s: %s", logDir, err)
}
}
fullLogFile := fmt.Sprintf("%s/%s", logDir, logFile)
log.Infof("Started recording to %s", fullLogFile)
bash, err := exec.LookPath("bash")
if err != nil {
log.Errorf("Could not locate bash: %v", err)
}
f, err := os.Create(fullLogFile)
if err != nil {
log.Fatalf("Failed to open device logs: %s", err)
}
command := exec.Command(bash, "-c", "python")
out := io.MultiWriter(os.Stdout, f)
command.Stderr = out
command.Stdout = out
if err := command.Start(); nil != err {
log.Fatalf("Error starting program: %s, %s", command.Path, err.Error())
}
err = command.Wait()
if err != nil {
log.Fatalf("Error waiting program: %s, %s", command.Path, err.Error())
}
f.Close()
log.Infof("Finished recording to %s", fullLogFile)
}
Tried this too without success :
out := io.MultiWriter(os.Stdout, f)
in := io.TeeReader(os.Stdin, out)
command.Stderr = out
command.Stdout = out
command.Stdin = in
You need to write to the process's stdin. Get a write pipe to that:
procIn, err := command.StdinPipe()
if nil!=err {
log.Fatal(err)
}
Then create a multiWriter to write to both log and process:
inWriter := io.MultiWriter(procIn, f)
Finally, copy Stdin into the MultiWriter:
go func() {
io.Copy(inWriter, os.Stdin)
procIn.Close()
}()
We do the copy in a goroutine, so as not to hang everything up: we haven't started the command yet, so there's nothing receiving the written bytes. It needs to occur in parallel to the command running.
Here's a very simple example:
package main
import (
`os`
`os/exec`
`io`
)
// pipeto copies stdin to logOut and to the command,
// and copies the commands stdout and stderr to logOut and
// to our stderr.
func pipeto(logOut os.Writer, cmd string, args ...string) error {
cmd := exec.Command(cmd, args...)
out := io.MultiWriter(os.Stdout, logOut)
cmd.Stderr, cmd.Stdout = out, out
procIn, err := cmd.StdinPipe()
if nil!=err {
return err
}
go func() {
io.Copy( io.MultiWriter(procIn, logOut) , os.Stdin )
procIn.Close()
}()
return cmd.Run()
}
func main() {
logOut, err := os.Create(`logout.log`)
if nil!=err {
panic(err)
}
defer logOut.Close()
if err := pipeto(logOut, `sed`, `s/tea/coffee/g`); nil!=err {
panic(err)
}
}
You can test it, where I've named my go file pipetest.go:
echo this is a test of tea | go run pipetest.go
The you will see both the input and the output reflected in logout.log:
this is a test of tea
this is a test of coffee
At the end I found the solution by using the PTY library (That would have been needed anyway to handle special signals and tabs on subprocesses): https://github.com/creack/pty
I took the Shell example and just replaced the io.Copy with my MultiWriter
I am trying to write a file from a bash command into a file in Go.
Note there are several reasons for using Go over bash here: I have some more logic such as parsing configuration files, I would like to run that code for multiple DBs in parallele and finally performing some more complex data manipulation after.
dumpStr := fmt.Sprintf("pg_dump -U %s -h %s %s | gzip", DbUserName, DbHost, DbName)
cmd := exec.Command("bash", "-c", dumpStr)
cmd.Env = append(cmd.Env, "PGPASSWORD="+DbPassword)
outfile, err := os.Create(DbName + ".gz")
if err != nil {
panic(err)
}
outfile = cmd.Stdout
defer outfile.Close()
err = cmd.Start()
if err != nil {
panic(err)
}
cmd.Wait()
However, I am getting an emtpy result.
I am getting data if I am executing dumpStr from the CLI but not from that code...
What am I missing?
As Flimzy said, you're not capturing the output of pg_dump. You can do that with Go, or you can use pg_dump-s --file. It can also compress with --compress so no need to pipe to gzip. Then there's no need for bash and you can avoid shell quoting issues.
cmd := exec.Command(
"pg_dump",
"--compress=9",
"--file="+DbName + ".gz",
"-U"+DbUserName,
"-h"+DbHost,
DbName,
)
log.Print("Running pg_dump...")
if err := cmd.Run(); err != nil {
log.Fatal(err)
}
Much simpler and more secure.
For illustration here's how you'd do it all in Go.
Use Cmd.StdoutPipe to get an open IO reader to pg_dump's stdout. Then use io.Copy to copy from stdout to your open file.
#Peter points out that since Cmd.Stdout is an io.Reader it's simpler to assign the open file to cmd.Stdout and let cmd write to it directly.
// Same as above, but no --file.
cmd := exec.Command(
"pg_dump",
"--compress=9",
"-U"+DbUserName,
"-h"+DbHost,
DbName,
)
// Open the output file
outfile, err := os.Create(DbName + ".gz")
if err != nil {
log.Fatal(err)
}
defer outfile.Close()
// Send stdout to the outfile. cmd.Stdout will take any io.Writer.
cmd.Stdout = outfile
// Start the command
if err = cmd.Start(); err != nil {
log.Fatal(err)
}
log.Print("Waiting for command to finish...")
// Wait for the command to finish.
if err = cmd.Wait(); err != nil {
log.Fatal(err)
}
In addition, you're only checking if the command started, not if it successfully ran.
From the docs for Cmd.Start.
Start starts the specified command but does not wait for it to complete.
The Wait method will return the exit code and release associated resources once the command exits.
You're checking cmd.Start for an error, but not cmd.Wait. Checking the error from cmd.Start only means the command started. If there is an error while the program is running you won't know what it is.
You need to actually use the output of your command. You're not doing that. To do so, use the StdoutPipe method, then you can copy the stdout from your program, into your file.
I'm trying to run a command in Golang, but it looks like it loses the exit code because the err is nil:
func runCommand() []byte, error {
cmd := exec.Command("/bin/bash", "-c", "KUBECONFIG=/tmp/.kube/config helm version")
cmd.Stdin = os.Stdin
cmd.Stderr = os.Stderr
stdOut, err := cmd.StdoutPipe()
if err != nil {
return nil, err
}
if err := cmd.Start(); err != nil {
return nil, err
}
bytes, err := ioutil.ReadAll(stdOut)
if err != nil {
return nil, err
}
if err := cmd.Wait(); err != nil {
return nil, err
}
fmt.Println(string(bytes))
return bytes, nil
}
This return nil, even though the command returns with exit code != 0.
If I type:
$> /bin/bash -c KUBECONFIG=/tmp/.kube/config helm version
$<
$> echo $?
$< 0
If I type:
$> /bin/bash -c 'KUBECONFIG=/tmp/.kube/config helm version'
$< ...connection refused
$> echo $?
$< 1
So I tried to wrap the command in single quote:
cmd := exec.Command("/bin/bash", "-c", "'KUBECONFIG=/tmp/.kube/config helm version'")
but then I get:
/bin/bash: KUBECONFIG=/tmp/.kube/config helm version: No such file or directory
(needless to say that /tmp/.kube/config is there, but I don't think the no such file or directory refers to that anyway).
What am I doing wrong?
Thanks
UPDATE: turns out I got it wrong. In fact I had two commands attempted and for some reason I was sure the one failing was the one I mentioned above, when instead the second command was exiting with a status code different from 0. The code works as expected and the err is not nil in case of exit code != 0. Sorry about that.
Seems like you should be able to get it with exec.ExitError, see exec package. Note that you may need Go 1.12. Here's a runnable example (but it won't give you realistic output at the go playground):
package main
import (
"fmt"
"io/ioutil"
"os"
"os/exec"
)
func main() {
cmd := exec.Command(`/bin/bash`, `-c`, `FOO=bar ls /foo`)
cmd.Stdin = os.Stdin
cmd.Stderr = os.Stderr
stdOut, err := cmd.StdoutPipe()
if err != nil {
fmt.Println("Error 1")
}
if err := cmd.Start(); err != nil {
fmt.Println("Error 2")
}
bytes, err := ioutil.ReadAll(stdOut)
if err != nil {
fmt.Println("Error 3")
}
if err := cmd.Wait(); err != nil {
fmt.Println("Error 4")
if exitError, ok := err.(*exec.ExitError); ok {
fmt.Printf("Exit code is %d\n", exitError.ExitCode())
}
}
fmt.Println(string(bytes))
}
On my system that prints:
$ go run main.go
ls: cannot access '/foo': No such file or directory
Error 4
Exit code is 2
If that doesn't work for you, maybe it's worth following #JimB's suggestion and invoking helm directly? The Go standard library should support pipes as well:
It wraps os.StartProcess to make it easier to remap stdin and stdout, connect I/O with pipes, and do other adjustments.
(exec package)
What I want to do is exporting a file from my server via SFTP, in golang.
Here is the troubling code
cmd = exec.Command("sftp", "login#sftp.com", `INPUT
cd /some/path
put file.gz
quit
INPUT`)
cmd.Stderr = &stderr
err = cmd.Run()
if err != nil {
fmt.Println(stderr.String())
os.Exit(1)
}
fmt.Println("done")
It gets to done but doesn't import file.gz.
I finally found the solution.
cmd = exec.Command("sftp", "login#sftp.com")
cmd.Stdin = strings.NewReader(`cd some/path
put file.gz
quit`)
cmd.Stderr = &stderr
err = cmd.Start()
if err != nil {
fmt.Println(stderr.String())
fmt.Println(err)
os.Exit(1)
}
err = cmd.Wait()
I set the commands I need to do once I'm in the STFP by setting cmd.Stdin
cmd.Start() and cmd.Wait() starts the command and stops when the whole command is done.
I'm trying to run a fairly simple bash command from my Go code. My program writes out an IPTables config file and I need to issue a command to make IPTables refresh from this config. This is very straightforward at the commandline:
/sbin/iptables-restore < /etc/iptables.conf
However, I can't for the life of me figure out how to issue this command with exec.Command(). I tried a few things to accomplish this:
cmd := exec.Command("/sbin/iptables-restore", "<", "/etc/iptables.conf")
// And also
cmd := exec.Command("/sbin/iptables-restore", "< /etc/iptables.conf")
No surprise, neither of those worked. I also tried to feed the filename into the command by piping in the file name to stdin:
cmd := exec.Command("/sbin/iptables-restore")
stdin, err := cmd.StdinPipe()
if err != nil {
log.Fatal(err)
}
err = cmd.Start()
if err != nil {
log.Fatal(err)
}
io.WriteString(stdin, "/etc/iptables.conf")
That doesn't work either, no surprise. I can use stdin to pipe in the contents of the file, but this seems silly when I can just tell iptables-restore what data to go read. So how might I get Go to run the command /sbin/iptables-restore < /etc/iptables.conf?
first read this /etc/iptables.conf file content then write it to cmd.StdinPipe() like this:
package main
import (
"io"
"io/ioutil"
"log"
"os/exec"
)
func main() {
bytes, err := ioutil.ReadFile("/etc/iptables.conf")
if err != nil {
log.Fatal(err)
}
cmd := exec.Command("/sbin/iptables-restore")
stdin, err := cmd.StdinPipe()
if err != nil {
log.Fatal(err)
}
err = cmd.Start()
if err != nil {
log.Fatal(err)
}
_, err = io.WriteString(stdin, string(bytes))
if err != nil {
log.Fatal(err)
}
}
cmd := exec.Command("/usr/sbin/iptables-restore", "--binary", iptablesFilePath)
_, err := cmd.CombinedOutput()
if err != nil {
return err
}
return nil
this work fine on my Raspberry Pi3
The os/exec package does not invoke the system shell, nor does it implement the < redirection syntax typically handled by a shell.
Open the input file and use that file as stdin:
stdin, err := os.Open("/etc/iptables.conf")
if err != nil {
log.Fatal(err)
}
defer stdin.Close()
cmd := exec.Command("/sbin/iptables-restore")
cmd.Stdin = stdin // <-- use open file as stdin
result, err := cmd.CombinedOutput()
if err != nil {
log.Fatal(err)
}
fmt.Printf("%s\n", result)