I want to create a simple program using Go that can get an output in the terminal output. For example:
echo "john" | goprogram
The output is hi john
When using command cat
cat list_name.txt | goprogram
The output using
hi doe
hi james
hi chris
Is there a way to do this using Go?
Read from os.Stdin. Here's an example implementation of the Hi program.
package main
import (
"bufio"
"fmt"
"log"
"os"
)
func main() {
s := bufio.NewScanner(os.Stdin)
for s.Scan() {
fmt.Println("hi", s.Text())
}
if s.Err() != nil {
log.Fatal(s.Err())
}
}
This program creates a scanner to read os.Stdin by line. For each line in stdin, the program prints "hi" and the line.
Related
How do I pass a list as a flag variable in Golang? For example in Bash you can pass a list as getopts to the script. Something like that:
./myScript.sh -n list_of_names.txt //some file with about 50 names
and later loop over the list:
#!/bin/bash
while getopts "n:h:" options; do
case "${options}" in
"n") NAME=${OPTARG};;
"h") PRINT_USAGE;;
esac
done
for i in $NAME; do
//TODO
I've heard about the "flag" package, but I have no idea how to achieve that
PS I'm a complete newbie to Go
In your example, you really only have one required argument, so you don't really need to parse anything. You can just check the slice length:
package main
import "os"
func main() {
if len(os.Args) != 2 {
println("myScript <file>")
os.Exit(1)
}
name := os.Args[1]
println(name)
}
https://golang.org/pkg/os#Args
As per the golang documentation, go does not make a call to the system's shell when you are using exec.Command().
From the golang.org documentation on the "os/exec" package:
Unlike the "system" library call from C and other languages, the os/exec package intentionally does not invoke the system shell and does not expand any glob patterns or handle other expansions, pipelines, or redirections typically done by shells.
This presents a problem. Because of this design choice you cannot use piping when executing a command. Therefore the following code does not execute as desired.
package main
import (
"fmt"
"os/exec"
)
func main() {
exec.Command("echo", "Hello", ">>", "~/thing").Run()
cmdOut, _ := exec.Command("cat", "~/thing").Output()
fmt.Println(cmdOut)
}
Instead of printing out the contents of a file that should contain the word 'Hello,' it instead prints out a blank newline. I have tried directly invoking bash like this:
package main
import (
"fmt"
"os/exec"
)
func main() {
exec.Command("bash", "-c", "echo", "Hello", ">>", "~/thing").Run()
cmdOut, _ := exec.Command("cat", "~/thing").Output()
fmt.Println(cmdOut)
}
This, however, produces the same result as the original code. How can I directly invoke the system shell when using golang?
The second argument should be one string. In shell command you need to pass it as one string too. Also ~ is interpreted by bash. You can safely assume that sh exists. Bash shell is not a must.
package main
import (
"fmt"
"os/exec"
)
func main() {
exec.Command("sh", "-c", "echo Hello >> ~/thing").Run()
cmdOut, _ := exec.Command("sh", "-c", "cat ~/thing").Output()
fmt.Println(cmdOut)
}
How do I read string argument include & in Go for example this link
$ ./main
https://www.youtube.com/watch?v=G3PvTWRIhZA&list=PLQVvvaa0QuDeF3hP0wQoSxpkqgRcgxMqX
without use double quotation (")
$ ./main
"https://www.youtube.com/watch?v=G3PvTWRIhZA&list=PLQVvvaa0QuDeF3hP0wQoSxpkqgRcgxMqX"
main.go
package main
import (
"os"
"fmt"
)
func main() {
link := os.Args[1]
fmt.Println(link)
}
$ go build main.go
$ ./main
https://www.youtube.com/watch?v=G3PvTWRIhZA&list=PLQVvvaa0QuDeF3hP0wQoSxpkqgRcgxMqX
output will be
https://www.youtube.com/watch?v=G3PvTWRIhZA
Both #JimB and #Adrian are correct, the & needs to be escaped.
If you absolutely must find a workaround, you could opt to not use a command-line argument and rather read input instead to bypass need for escaping.
Example:
package main
import (
"fmt"
)
func main() {
var input string
fmt.Scan(&input)
fmt.Println(input)
}
input:
$ ./main
https://www.youtube.com/watch?v=G3PvTWRIhZA&list=PLQVvvaa0QuDeF3hP0wQoSxpkqgRcgxMqX
output:
https://www.youtube.com/watch?v=G3PvTWRIhZA&list=PLQVvvaa0QuDeF3hP0wQoSxpkqgRcgxMqX
I want to escape a restricted shell spawning a bash shell via Go. In other words, I want to do this but using Go:
python -c 'import pty; pty.spawn("/bin/bash")'
I am totally new to Go. I have tried this (following the answer in this question Go: How to spawn a bash shell) but nothing happens:
package main
import "os"
import "os/exec"
func main() {
shell := exec.Command("/bin/bash")
shell.Stdout = os.Stdout
shell.Stdin = os.Stdin
shell.Stderr = os.Stderr
shell.Run()
}
Also if I add the fmt.Println("hello") line at the end of the main function nothing is printed
UPDATE
Maybe I did not expalined well. What I am trying to achieve it's to spawn a shell gotten a restricted shell. This is what I did:
Listener:
nc.traditional -l -p 8080 -e /bin/bash
Connects to listener: And I exec the code here
nc.traditional localhost 8080 -v
Your program works fine for me. I put some error checking in and an extra print statement which should make what is happening clearer. You are getting an interactive shell, it just looks exactly like your previous shell.
$ go run Go/shell.go
$ # whoa another shell
$ exit
exit
exiting
$ # back again
$
Here is the revised program
package main
import (
"fmt"
"log"
"os"
"os/exec"
)
func main() {
shell := exec.Command("/bin/bash")
shell.Stdout = os.Stdout
shell.Stdin = os.Stdin
shell.Stderr = os.Stderr
err := shell.Run()
if err != nil {
log.Fatalf("command failed: %v", err)
}
fmt.Printf("exiting\n")
}
For fun and to better learn Go, I'm trying to re-implement antigen in Go.
Problem is: source is a shell built-in function, so I can't call it with os/exec Command function, because it expects an executable in PATH.
How can I do this? And, is it possible to make a source from inside a go program affect the user shell?
You can write the command directly in the terminal device. But, to do that, first you need to know which device is using the user. A script that executes your program can be a solution.
#!/bin/bash
echo Running from foo script, pid = $$
go run foo.go `tty`
Then, the program has to write the commands to the terminal device.
package main
import (
"C"
"fmt"
"os"
"syscall"
"unsafe"
)
func main() {
// Get tty path
if len(os.Args) < 2 {
fmt.Printf("no tty path\n")
os.Exit(1)
}
ttyPath := os.Args[1]
// Open tty
tty, err := os.Open(ttyPath)
if err != nil {
fmt.Printf("error opening tty: %s\n", err.Error())
os.Exit(2)
}
defer tty.Close()
// Write a command
cmd := "echo Hello from go, pid = $$\n"
cmdstr := C.CString(cmd)
cmdaddr := uintptr(unsafe.Pointer(cmdstr))
for i := range []byte(cmd) {
_, _, err := syscall.Syscall(syscall.SYS_IOCTL, tty.Fd(), syscall.TIOCSTI, cmdaddr+uintptr(i))
if uintptr(err) != 0 {
fmt.Printf("syscall error: %s\n", err.Error())
os.Exit(3)
}
}
}
Here is an example output:
$ echo $$
70318
$ ./foo
Running from foo script, pid = 83035
echo Hello from go, pid = $$
$ echo Hello from go, pid = $$
Hello from go, pid = 70318
Note that I am executing the script with ./ not source, so the PID of the script differs. But later, the command executed by the go program has the same PID.