package exec

Import Path
	os/exec (on golang.org and go.dev)

Dependency Relation
	imports 13 packages, and imported by 5 packages


Involved Source Files

	
		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.

	      exec_unix.go
	      lp_unix.go


Code Examples

	
		package main
		
		import (
			"fmt"
			"log"
			"os/exec"
		)
		
		func main() {
			cmd := exec.Command("sh", "-c", "echo stdout; echo 1>&2 stderr")
			stdoutStderr, err := cmd.CombinedOutput()
			if err != nil {
				log.Fatal(err)
			}
			fmt.Printf("%s\n", stdoutStderr)
		}


	
		package main
		
		import (
			"fmt"
			"log"
			"os/exec"
		)
		
		func main() {
			out, err := exec.Command("date").Output()
			if err != nil {
				log.Fatal(err)
			}
			fmt.Printf("The date is %s\n", out)
		}


	
		package main
		
		import (
			"log"
			"os/exec"
		)
		
		func main() {
			cmd := exec.Command("sleep", "1")
			log.Printf("Running command and waiting for it to finish...")
			err := cmd.Run()
			log.Printf("Command finished with error: %v", err)
		}


	
		package main
		
		import (
			"log"
			"os/exec"
		)
		
		func main() {
			cmd := exec.Command("sleep", "5")
			err := cmd.Start()
			if err != nil {
				log.Fatal(err)
			}
			log.Printf("Waiting for command to finish...")
			err = cmd.Wait()
			log.Printf("Command finished with error: %v", err)
		}


	
		package main
		
		import (
			"fmt"
			"io"
			"log"
			"os/exec"
		)
		
		func main() {
			cmd := exec.Command("sh", "-c", "echo stdout; echo 1>&2 stderr")
			stderr, err := cmd.StderrPipe()
			if err != nil {
				log.Fatal(err)
			}
		
			if err := cmd.Start(); err != nil {
				log.Fatal(err)
			}
		
			slurp, _ := io.ReadAll(stderr)
			fmt.Printf("%s\n", slurp)
		
			if err := cmd.Wait(); err != nil {
				log.Fatal(err)
			}
		}


	
		package main
		
		import (
			"fmt"
			"io"
			"log"
			"os/exec"
		)
		
		func main() {
			cmd := exec.Command("cat")
			stdin, err := cmd.StdinPipe()
			if err != nil {
				log.Fatal(err)
			}
		
			go func() {
				defer stdin.Close()
				io.WriteString(stdin, "values written to stdin are passed to cmd's standard input")
			}()
		
			out, err := cmd.CombinedOutput()
			if err != nil {
				log.Fatal(err)
			}
		
			fmt.Printf("%s\n", out)
		}


	
		package main
		
		import (
			"encoding/json"
			"fmt"
			"log"
			"os/exec"
		)
		
		func main() {
			cmd := exec.Command("echo", "-n", `{"Name": "Bob", "Age": 32}`)
			stdout, err := cmd.StdoutPipe()
			if err != nil {
				log.Fatal(err)
			}
			if err := cmd.Start(); err != nil {
				log.Fatal(err)
			}
			var person struct {
				Name string
				Age  int
			}
			if err := json.NewDecoder(stdout).Decode(&person); err != nil {
				log.Fatal(err)
			}
			if err := cmd.Wait(); err != nil {
				log.Fatal(err)
			}
			fmt.Printf("%s is %d years old\n", person.Name, person.Age)
		}


	
		package main
		
		import (
			"bytes"
			"fmt"
			"log"
			"os/exec"
			"strings"
		)
		
		func main() {
			cmd := exec.Command("tr", "a-z", "A-Z")
			cmd.Stdin = strings.NewReader("some input")
			var out bytes.Buffer
			cmd.Stdout = &out
			err := cmd.Run()
			if err != nil {
				log.Fatal(err)
			}
			fmt.Printf("in all caps: %q\n", out.String())
		}


	
		package main
		
		import (
			"context"
			"os/exec"
			"time"
		)
		
		func main() {
			ctx, cancel := context.WithTimeout(context.Background(), 100*time.Millisecond)
			defer cancel()
		
			if err := exec.CommandContext(ctx, "sleep", "5").Run(); err != nil {
				// This will fail after 100 milliseconds. The 5 second sleep
				// will be interrupted.
			}
		}


	
		package main
		
		import (
			"log"
			"os"
			"os/exec"
		)
		
		func main() {
			cmd := exec.Command("prog")
			cmd.Env = append(os.Environ(),
				"FOO=duplicate_value", // ignored
				"FOO=actual_value",    // this value is used
			)
			if err := cmd.Run(); err != nil {
				log.Fatal(err)
			}
		}


	
		package main
		
		import (
			"fmt"
			"log"
			"os/exec"
		)
		
		func main() {
			path, err := exec.LookPath("fortune")
			if err != nil {
				log.Fatal("installing fortune is in your future")
			}
			fmt.Printf("fortune is available at %s\n", path)
		}




Package-Level Type Names (total 3)


	/* sort by:  |  */
	
		Cmd represents an external command being prepared or run.

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

		
			
				Args holds command line arguments, including the command as Args[0].
				If the Args field is empty or nil, Run uses {Path}.

				In typical use, both Path and Args are set by calling Command.

			
				Dir specifies the working directory of the command.
				If Dir is the empty string, Run runs the command in the
				calling process's current directory.

			
				Env specifies the environment of the process.
				Each entry is of the form "key=value".
				If Env is nil, the new process uses the current process's
				environment.
				If Env contains duplicate environment keys, only the last
				value in the slice for each duplicate key is used.
				As a special case on Windows, SYSTEMROOT is always added if
				missing and not explicitly set to the empty string.

			
				ExtraFiles specifies additional open files to be inherited by the
				new process. It does not include standard input, standard output, or
				standard error. If non-nil, entry i becomes file descriptor 3+i.

				ExtraFiles is not supported on Windows.

			
				Path is the path of the command to run.

				This is the only field that must be set to a non-zero
				value. If Path is relative, it is evaluated relative
				to Dir.

			
				Process is the underlying process, once started.

			
				ProcessState contains information about an exited process,
				available after a call to Wait or Run.

			Stderr io.Writer
			
				Stdin specifies the process's standard input.

				If Stdin is nil, the process reads from the null device (os.DevNull).

				If Stdin is an *os.File, the process's standard input is connected
				directly to that file.

				Otherwise, during the execution of the command a separate
				goroutine reads from Stdin and delivers that data to the command
				over a pipe. In this case, Wait does not complete until the goroutine
				stops copying, either because it has reached the end of Stdin
				(EOF or a read error) or because writing to the pipe returned an error.

			
				Stdout and Stderr specify the process's standard output and error.

				If either is nil, Run connects the corresponding file descriptor
				to the null device (os.DevNull).

				If either is an *os.File, the corresponding output from the process
				is connected directly to that file.

				Otherwise, during the execution of the command a separate goroutine
				reads from the process over a pipe and delivers that data to the
				corresponding Writer. In this case, Wait does not complete until the
				goroutine reaches EOF or encounters an error.

				If Stdout and Stderr are the same writer, and have a type that can
				be compared with ==, at most one goroutine at a time will call Write.

			
				SysProcAttr holds optional, operating system-specific attributes.
				Run passes it to os.StartProcess as the os.ProcAttr's Sys field.

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

			
				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.

			
				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.

			
				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.

			
				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.

			
				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.

			
				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.

			
				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.

			
				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.

		
			*T : expvar.Var
			*T : fmt.Stringer
		
			func Command(name string, arg ...string) *Cmd
			func CommandContext(ctx context.Context, name string, arg ...string) *Cmd
			func internal/execabs.Command(name string, arg ...string) *Cmd
			func internal/execabs.CommandContext(ctx context.Context, name string, arg ...string) *Cmd
			func internal/testenv.CleanCmdEnv(cmd *Cmd) *Cmd
		
			func internal/testenv.CleanCmdEnv(cmd *Cmd) *Cmd


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

		
			
				Err is the underlying error.

			
				Name is the file name for which the error occurred.

		
			(*T) Error() string
			(*T) Unwrap() error
		
			*T : error


	
		An ExitError reports an unsuccessful exit by a command.

		
			ProcessState *os.ProcessState
			
				Stderr holds a subset of the standard error output from the
				Cmd.Output method if standard error was not otherwise being
				collected.

				If the error output is long, Stderr may contain only a prefix
				and suffix of the output, with the middle replaced with
				text about the number of omitted bytes.

				Stderr is provided for debugging, for inclusion in error messages.
				Users with other needs should redirect Cmd.Stderr as needed.

		
			(*T) Error() string
			
				ExitCode returns the exit code of the exited process, or -1
				if the process hasn't exited or was terminated by a signal.

			
				Exited reports whether the program has exited.

			
				Pid returns the process id of the exited process.

			( T) String() string
			
				Success reports whether the program exited successfully,
				such as with exit status 0 on Unix.

			
				Sys returns system-dependent exit information about
				the process. Convert it to the appropriate underlying
				type, such as syscall.WaitStatus on Unix, to access its contents.

			
				SysUsage returns system-dependent resource usage information about
				the exited process. Convert it to the appropriate underlying
				type, such as *syscall.Rusage on Unix, to access its contents.
				(On Unix, *syscall.Rusage matches struct rusage as defined in the
				getrusage(2) manual page.)

			
				SystemTime returns the system CPU time of the exited process and its children.

			
				UserTime returns the user CPU time of the exited process and its children.

		
			*T : error
			 T : expvar.Var
			 T : fmt.Stringer




Package-Level Functions (total 3)


	
		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.


	
		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.


	
		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.




Package-Level Variables (only one)


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