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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.
// The exec package runs external commands.
package exec
import (
"os"
"strings"
)
// 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.
// Pid is the running command's operating system process ID.
type Cmd struct {
Stdin *os.File
Stdout *os.File
Stderr *os.File
Pid int
}
// 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.Open("/dev/null", 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 binary prog running with
// arguments argv and environment envv.
// It returns a pointer to a new Cmd representing
// the command or an error.
//
// The parameters 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 a parameter 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(argv0 string, argv, envv []string, dir string, stdin, stdout, stderr int) (p *Cmd, err os.Error) {
p = new(Cmd)
var fd [3]*os.File
if fd[0], p.Stdin, err = modeToFiles(stdin, 0); err != nil {
goto Error
}
if fd[1], p.Stdout, err = modeToFiles(stdout, 1); err != nil {
goto Error
}
if stderr == MergeWithStdout {
fd[2] = fd[1]
} else if fd[2], p.Stderr, err = modeToFiles(stderr, 2); err != nil {
goto Error
}
// Run command.
p.Pid, err = os.ForkExec(argv0, argv, envv, dir, fd[0:])
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 p, 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 p.Stdin != nil {
p.Stdin.Close()
}
if p.Stdout != nil {
p.Stdout.Close()
}
if p.Stderr != nil {
p.Stderr.Close()
}
return nil, err
}
// Wait waits for the running command p,
// returning the Waitmsg returned by os.Wait and an error.
// The options are passed through to os.Wait.
// Setting options to 0 waits for p to exit;
// other options cause Wait to return for other
// process events; see package os for details.
func (p *Cmd) Wait(options int) (*os.Waitmsg, os.Error) {
if p.Pid <= 0 {
return nil, os.ErrorString("exec: invalid use of Cmd.Wait")
}
w, err := os.Wait(p.Pid, options)
if w != nil && (w.Exited() || w.Signaled()) {
p.Pid = -1
}
return w, err
}
// Close waits for the running command p to exit,
// if it hasn't already, and then closes the non-nil file descriptors
// p.Stdin, p.Stdout, and p.Stderr.
func (p *Cmd) Close() os.Error {
if p.Pid > 0 {
// Loop on interrupt, but
// ignore other errors -- maybe
// caller has already waited for pid.
_, err := p.Wait(0)
for err == os.EINTR {
_, err = p.Wait(0)
}
}
// Close the FDs that are still open.
var err os.Error
if p.Stdin != nil && p.Stdin.Fd() >= 0 {
if err1 := p.Stdin.Close(); err1 != nil {
err = err1
}
}
if p.Stdout != nil && p.Stdout.Fd() >= 0 {
if err1 := p.Stdout.Close(); err1 != nil && err != nil {
err = err1
}
}
if p.Stderr != nil && p.Stderr != p.Stdout && p.Stderr.Fd() >= 0 {
if err1 := p.Stderr.Close(); err1 != nil && err != nil {
err = err1
}
}
return err
}
func canExec(file string) bool {
d, err := os.Stat(file)
if err != nil {
return false
}
return d.IsRegular() && d.Permission()&0111 != 0
}
// LookPath searches for an executable binary 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.
//
// TODO(rsc): Does LookPath belong in os instead?
func LookPath(file string) (string, os.Error) {
// NOTE(rsc): I wish we could use the Plan 9 behavior here
// (only bypass the path if file begins with / or ./ or ../)
// but that would not match all the Unix shells.
if strings.Index(file, "/") >= 0 {
if canExec(file) {
return file, nil
}
return "", os.ENOENT
}
pathenv := os.Getenv("PATH")
for _, dir := range strings.Split(pathenv, ":", 0) {
if dir == "" {
// Unix shell semantics: path element "" means "."
dir = "."
}
if canExec(dir + "/" + file) {
return dir + "/" + file, nil
}
}
return "", os.ENOENT
}
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