Golang exec command linux

Go exec command

last modified October 13, 2020

Go exec command tutorial shows how to execute shell commands and programs in Golang.

The Run function starts the specified command and waits for it to complete, while the Start starts the specified command but does not wait for it to complete; we need to use Wait with Start .

Go os/exec

The os/exec package runs external commands. It wraps os.StartProcess to make it easier to remap stdin and stdout, connect I/O with pipes, and do other adjustments.

Go exec program

The Run starts the specified command and waits for it to complete.

In the example, we execute the Firefox browser.

Go exec.Command

The Command returns the Cmd struct to execute the specified program with the given arguments. The first parameter is the program to be run; the other arguments are parameters to the program.

In the example, we transform the input via the tr command.

The tr standard Linux command translates, squeezes, and/or deletes characters from standard input, writing to standard output. In our case, we transform lowercase letters to uppercase ones.

Through the Stdin field, we pass a string to the command as its input.

The output of the program will be written to the bytes buffer.

This is the output.

Go exec command with multiple args

We can pass multiple arguments to the exec.Command .

The example runs the echo command with three arguments.

This is the output.

Go exec command capture output

The Output runs the command and returns its standard output.

The example captures the output of the ls command and prints it.

Go cmd.StdinPipe

The pipe allows us to send the output of one command to another. The StdinPipe returns a pipe that will be connected to the command’s standard input when the command starts.

In the example, we write a string to the standard input inside a goroutine.

The cat command concatenates the given files to the standard output. When no file is given, or with -, the command reads standard input and prints it to standard output.

We get the standard input pipe of the cat command.

Inside the goroutine, we write a string to the stdin pipe.

This is the output.

Go cmd.StdoutPipe

The StdoutPipe returns a pipe that will be connected to the command’s standard output when the command starts.

The example reads the output of the echo command through the pipe and transforms it into uppercase letters.

The command to run is the echo command with a single string argument.

We get the standard output pipe.

The command is executed with the Start function; it does not wait wait for it to complete.

We read the data from the pipe.

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.

This is the output.

In this tutorial, we have executed external commands in Golang.

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Golang exec command linux

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Repository

Documentation ¶

Overview ¶

Package exec runs external commands. It wraps os.StartProcess to make it easier to remap stdin and stdout, connect I/O with pipes, and do other adjustments.

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. The package behaves more like C’s «exec» family of functions. To expand glob patterns, either call the shell directly, taking care to escape any dangerous input, or use the path/filepath package’s Glob function. To expand environment variables, use package os’s ExpandEnv.

Note that the examples in this package assume a Unix system. They may not run on Windows, and they do not run in the Go Playground used by golang.org and godoc.org.

Index ¶

Examples ¶

Constants ¶

This section is empty.

Variables ¶

ErrNotFound is the error resulting if a path search failed to find an executable file.

Functions ¶

func LookPath ¶

LookPath searches for an executable named file in the directories named by the PATH environment variable. If file contains a slash, it is tried directly and the PATH is not consulted. The result may be an absolute path or a path relative to the current directory.

Share Format Run

Types ¶

type Cmd ¶

Cmd represents an external command being prepared or run.

A Cmd cannot be reused after calling its Run, Output or CombinedOutput methods.

func Command ¶

Command returns the Cmd struct to execute the named program with the given arguments.

It sets only the Path and Args in the returned structure.

If name contains no path separators, Command uses LookPath to resolve name to a complete path if possible. Otherwise it uses name directly as Path.

The returned Cmd’s Args field is constructed from the command name followed by the elements of arg, so arg should not include the command name itself. For example, Command(«echo», «hello»). Args[0] is always name, not the possibly resolved Path.

On Windows, processes receive the whole command line as a single string and do their own parsing. Command combines and quotes Args into a command line string with an algorithm compatible with applications using CommandLineToArgvW (which is the most common way). Notable exceptions are msiexec.exe and cmd.exe (and thus, all batch files), which have a different unquoting algorithm. In these or other similar cases, you can do the quoting yourself and provide the full command line in SysProcAttr.CmdLine, leaving Args empty.

Share Format Run

Share Format Run

func CommandContext ¶ added in go1.7

CommandContext is like Command but includes a context.

The provided context is used to kill the process (by calling os.Process.Kill) if the context becomes done before the command completes on its own.

Share Format Run

func (*Cmd) CombinedOutput ¶

CombinedOutput runs the command and returns its combined standard output and standard error.

Share Format Run

func (*Cmd) Output ¶

Output runs the command and returns its standard output. Any returned error will usually be of type *ExitError. If c.Stderr was nil, Output populates ExitError.Stderr.

Share Format Run

func (*Cmd) Run ¶

Run starts the specified command and waits for it to complete.

The returned error is nil if the command runs, has no problems copying stdin, stdout, and stderr, and exits with a zero exit status.

If the command starts but does not complete successfully, the error is of type *ExitError. Other error types may be returned for other situations.

If the calling goroutine has locked the operating system thread with runtime.LockOSThread and modified any inheritable OS-level thread state (for example, Linux or Plan 9 name spaces), the new process will inherit the caller’s thread state.

Share Format Run

func (*Cmd) Start ¶

Start starts the specified command but does not wait for it to complete.

If Start returns successfully, the c.Process field will be set.

The Wait method will return the exit code and release associated resources once the command exits.

Share Format Run

func (*Cmd) StderrPipe ¶

StderrPipe returns a pipe that will be connected to the command’s standard error when the command starts.

Wait will close the pipe after seeing the command exit, so most callers need not close the pipe themselves. It is thus incorrect to call Wait before all reads from the pipe have completed. For the same reason, it is incorrect to use Run when using StderrPipe. See the StdoutPipe example for idiomatic usage.

Share Format Run

func (*Cmd) StdinPipe ¶

StdinPipe returns a pipe that will be connected to the command’s standard input when the command starts. The pipe will be closed automatically after Wait sees the command exit. A caller need only call Close to force the pipe to close sooner. For example, if the command being run will not exit until standard input is closed, the caller must close the pipe.

Share Format Run

func (*Cmd) StdoutPipe ¶

StdoutPipe returns a pipe that will be connected to the command’s standard output when the command starts.

Wait will close the pipe after seeing the command exit, so most callers need not close the pipe themselves. It is thus incorrect to call Wait before all reads from the pipe have completed. For the same reason, it is incorrect to call Run when using StdoutPipe. See the example for idiomatic usage.

Share Format Run

func (*Cmd) String ¶ added in go1.13

String returns a human-readable description of c. It is intended only for debugging. In particular, it is not suitable for use as input to a shell. The output of String may vary across Go releases.

func (*Cmd) Wait ¶

Wait waits for the command to exit and waits for any copying to stdin or copying from stdout or stderr to complete.

The command must have been started by Start.

The returned error is nil if the command runs, has no problems copying stdin, stdout, and stderr, and exits with a zero exit status.

If the command fails to run or doesn’t complete successfully, the error is of type *ExitError. Other error types may be returned for I/O problems.

If any of c.Stdin, c.Stdout or c.Stderr are not an *os.File, Wait also waits for the respective I/O loop copying to or from the process to complete.

Wait releases any resources associated with the Cmd.

type Error ¶

Error is returned by LookPath when it fails to classify a file as an executable.

Источник

Go для системных администраторов. Практические примеры. Часть 0

Здравствуйте, меня зовут Виталий и я обезьяна практик — для меня лучше один раз увидеть и скопировать, чем сто раз прочитать абстрактные руководства. Долгое время я был обычным системным администратором — писал скрипты на CMD/BAT, и даже на sh (при помощи busybox для Windows). Но однажды обычного shell мне стало не хватать, и я решил для себя написать собственный RPC-сервер, но так, чтобы он работал при минимуме системных компонентов, и был понятным, и был многопоточным и содержал минимум строк кода. Java и прочее ООП я отмел, так как для профессионалов, и слишком абстрактно, и надо ставить среду для выполнения на целевой компьютер, и мне же, как админу, её обновлять. Долгое время приглядывался к perl, но я боюсь динамической типизации. В статье я расскажу, как человеку мало знакомому с программированием решить некоторые задачи системного администрирования при помощи Go.

Я предполагаю, что вы осилили «Быстрый старт – программируем на Go под Windows — настройка Environment», имеете опыт написания простейших скриптов. А еще я соврал. На целевой машине может потребоваться Microsoft Visual C++.

Для начала мы попробуем превратить простой скрипт в приложение на Go. Для примера возьмем test.bat:

Минутка любви к Microsoft. Если я хочу проверить, скачался ли файл из второго источника, то я должен использовать GOTO, т. к. внутри IF и FOR %errorlevel% и %time% остаются такими же как перед вызовом IF и FOR.

Примерно так будет выглядеть наш скрипт на Go:

Запустить мы запустили, но для отладки неплохо было бы увидеть, что выдает curl в stderr/stdout. Кстати, curl все выдает в stderr:

При ошибке функция start_curl() возвращает что-то вроде «exit code 7». А нам бы хотелось получить код возврата в виде числа. Мы можем отрезать строку «exit_code » и и преобразовать строку «7» в число7. Для этого придется импортировать пакеты «strings» и «strconv». Но есть более простой, и менее понятный способ:

На сегодня все. Компилятор соберет нам готовый exe-файл. Бояться большого размера (несколько мегабайт) не нужно. В этот файл будут собраны минимальная среда исполнения и все необходимые пакеты. Потребление памяти приложением на Go раза в два меньше чем у perl или python(если мы конечно говорим о небольших приложениях). Если статья кого-то заинтересовала, в комментариях укажите, какую из тем хотелось бы рассмотреть:

• работа с текстом (парсинг stdout, кодировки)
• файлы(информация, поиск, ведение логов)
• работа с winapi(подключение dll, вызов функций, обработка ответов)
• работа с adodb(как прочитать данные из базы MSAccess)
• отправка e-mail средствами Go
• простой RPC-сервер

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How do I execute a command on a remote machine in a golang CLI?

How do I execute a command on a remote machine in a golang CLI? I need to write a golang CLI that can SSH into a remote machine via a key and execute a shell command. Furthermore, I need to be able to do this one hop away. e.g. SSH into a machine (like a cloud bastion) and then SSH into another, internal, machine and execute a shell command.

I haven’t (yet) found any examples for this.

5 Answers 5

Try with os/exec https://golang.org/pkg/os/exec/ to execute a ssh

To jump over machines use the ProxyCommand directive in a ssh config file.

You can run commands on a remote machine over SSH using the «golang.org/x/crypto/ssh» package.

Here is an example function demonstrating simple usage of running a single command on a remote machine and returning the output:

The other solutions here will work, but I’ll throw out another option you could try: simplessh. I think it is easier to use. For this question, I would use option 3 below where you can ssh using your key.

Option 1: SSH to a machine with a password, then run a command

Option 2: SSH to a machine using a set of possible passwords, then run a command

Option 3: SSH to a machine using your key

golang SSH executes shell command with timeout option

Not the answer you’re looking for? Browse other questions tagged go ssh command-line-interface or ask your own question.

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