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// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// 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.
package exec
// BUG(r): This package should be made even easier to use or merged into os.
import (
"os"
"strconv"
)
// Arguments to Run.
const (
DevNull = iota
PassThrough
Pipe
MergeWithStdout
)
// A Cmd represents a running command.
// Stdin, Stdout, and Stderr are Files representing pipes
// connected to the running command's standard input, output, and error,
// or else nil, depending on the arguments to Run.
// Process represents the underlying operating system process.
type Cmd struct {
Stdin *os.File
Stdout *os.File
Stderr *os.File
Process *os.Process
}
// PathError records the name of a binary that was not
// found on the current $PATH.
type PathError struct {
Name string
}
func (e *PathError) String() string {
return "command " + strconv.Quote(e.Name) + " not found in $PATH"
}
// Given mode (DevNull, etc), return file for child
// and file to record in Cmd structure.
func modeToFiles(mode, fd int) (*os.File, *os.File, os.Error) {
switch mode {
case DevNull:
rw := os.O_WRONLY
if fd == 0 {
rw = os.O_RDONLY
}
f, err := os.OpenFile(os.DevNull, rw, 0)
return f, nil, err
case PassThrough:
switch fd {
case 0:
return os.Stdin, nil, nil
case 1:
return os.Stdout, nil, nil
case 2:
return os.Stderr, nil, nil
}
case Pipe:
r, w, err := os.Pipe()
if err != nil {
return nil, nil, err
}
if fd == 0 {
return r, w, nil
}
return w, r, nil
}
return nil, nil, os.EINVAL
}
// Run starts the named binary running with
// arguments argv and environment envv.
// If the dir argument is not empty, the child changes
// into the directory before executing the binary.
// It returns a pointer to a new Cmd representing
// the command or an error.
//
// The arguments stdin, stdout, and stderr
// specify how to handle standard input, output, and error.
// The choices are DevNull (connect to /dev/null),
// PassThrough (connect to the current process's standard stream),
// Pipe (connect to an operating system pipe), and
// MergeWithStdout (only for standard error; use the same
// file descriptor as was used for standard output).
// If an argument is Pipe, then the corresponding field (Stdin, Stdout, Stderr)
// of the returned Cmd is the other end of the pipe.
// Otherwise the field in Cmd is nil.
func Run(name string, argv, envv []string, dir string, stdin, stdout, stderr int) (c *Cmd, err os.Error) {
c = new(Cmd)
var fd [3]*os.File
if fd[0], c.Stdin, err = modeToFiles(stdin, 0); err != nil {
goto Error
}
if fd[1], c.Stdout, err = modeToFiles(stdout, 1); err != nil {
goto Error
}
if stderr == MergeWithStdout {
fd[2] = fd[1]
} else if fd[2], c.Stderr, err = modeToFiles(stderr, 2); err != nil {
goto Error
}
// Run command.
c.Process, err = os.StartProcess(name, argv, &os.ProcAttr{Dir: dir, Files: fd[:], Env: envv})
if err != nil {
goto Error
}
if fd[0] != os.Stdin {
fd[0].Close()
}
if fd[1] != os.Stdout {
fd[1].Close()
}
if fd[2] != os.Stderr && fd[2] != fd[1] {
fd[2].Close()
}
return c, nil
Error:
if fd[0] != os.Stdin && fd[0] != nil {
fd[0].Close()
}
if fd[1] != os.Stdout && fd[1] != nil {
fd[1].Close()
}
if fd[2] != os.Stderr && fd[2] != nil && fd[2] != fd[1] {
fd[2].Close()
}
if c.Stdin != nil {
c.Stdin.Close()
}
if c.Stdout != nil {
c.Stdout.Close()
}
if c.Stderr != nil {
c.Stderr.Close()
}
if c.Process != nil {
c.Process.Release()
}
return nil, err
}
// Wait waits for the running command c,
// returning the Waitmsg returned when the process exits.
// The options are passed to the process's Wait method.
// Setting options to 0 waits for c to exit;
// other options cause Wait to return for other
// process events; see package os for details.
func (c *Cmd) Wait(options int) (*os.Waitmsg, os.Error) {
if c.Process == nil {
return nil, os.ErrorString("exec: invalid use of Cmd.Wait")
}
w, err := c.Process.Wait(options)
if w != nil && (w.Exited() || w.Signaled()) {
c.Process.Release()
c.Process = nil
}
return w, err
}
// Close waits for the running command c to exit,
// if it hasn't already, and then closes the non-nil file descriptors
// c.Stdin, c.Stdout, and c.Stderr.
func (c *Cmd) Close() os.Error {
if c.Process != nil {
// Loop on interrupt, but
// ignore other errors -- maybe
// caller has already waited for pid.
_, err := c.Wait(0)
for err == os.EINTR {
_, err = c.Wait(0)
}
}
// Close the FDs that are still open.
var err os.Error
if c.Stdin != nil && c.Stdin.Fd() >= 0 {
if err1 := c.Stdin.Close(); err1 != nil {
err = err1
}
}
if c.Stdout != nil && c.Stdout.Fd() >= 0 {
if err1 := c.Stdout.Close(); err1 != nil && err != nil {
err = err1
}
}
if c.Stderr != nil && c.Stderr != c.Stdout && c.Stderr.Fd() >= 0 {
if err1 := c.Stderr.Close(); err1 != nil && err != nil {
err = err1
}
}
return err
}
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