The POSIX::Spawn module implements a compatible subset of Ruby 1.9’s Process::spawn and related methods using the IEEE Std 1003.1 posix_spawn(2) system interfaces where available, or a pure Ruby fork/exec based implementation when not.
In Ruby 1.9, a versatile new process spawning interface was added (Process::spawn) as the foundation for enhanced versions of existing process-related methods like Kernel#system, Kernel#`, and IO#popen. These methods are backward compatible with their Ruby 1.8 counterparts but support a large number of new options. The POSIX::Spawn module implements many of these methods with support for most of Ruby 1.9’s features.
The argument signatures for all of these methods follow a new convention, making it possible to take advantage of Process::spawn features:
spawn([env], command, [argv1, ...], [options]) system([env], command, [argv1, ...], [options]) popen([[env], command, [argv1, ...]], mode="r", [options])
The env, command, and options arguments are described below.
If a hash is given in the first argument (env), the child process’s environment becomes a merge of the parent’s and any modifications specified in the hash. When a value in env is nil, the variable is unset in the child:
# set FOO as BAR and unset BAZ. spawn({"FOO" => "BAR", "BAZ" => nil}, 'echo', 'hello world')
The command and optional argvN string arguments specify the command to execute and any program arguments. When only command is given and includes a space character, the command text is executed by the system shell interpreter, as if by:
/bin/sh -c 'command'
When command does not include a space character, or one or more argvN arguments are given, the command is executed as if by execve(2) with each argument forming the new program’s argv.
NOTE: Use of the shell variation is generally discouraged unless you indeed want to execute a shell program. Specifying an explicitly argv is typically more secure and less error prone in most cases.
When a hash is given in the last argument (options), it specifies a current directory and zero or more fd redirects for the child process.
The :chdir option specifies the current directory. Note that :chdir is not thread-safe on systems that provide posix_spawn(2), because it forces a temporary change of the working directory of the calling process.
spawn(command, :chdir => "/var/tmp")
The :in, :out, :err, a Fixnum, an IO object or an Array option specify fd redirection. For example, stderr can be merged into stdout as follows:
spawn(command, :err => :out) spawn(command, 2 => 1) spawn(command, STDERR => :out) spawn(command, STDERR => STDOUT)
The key is a fd in the newly spawned child process (stderr in this case). The value is a fd in the parent process (stdout in this case).
You can also specify a filename for redirection instead of an fd:
spawn(command, :in => "/dev/null") # read mode spawn(command, :out => "/dev/null") # write mode spawn(command, :err => "log") # write mode spawn(command, 3 => "/dev/null") # read mode
When redirecting to stdout or stderr, the files are opened in write mode; otherwise, read mode is used.
It’s also possible to control the open flags and file permissions directly by passing an array value:
spawn(command, :in=>["file"]) # read mode assumed spawn(command, :in=>["file", "r"]) # explicit read mode spawn(command, :out=>["log", "w"]) # explicit write mode, 0644 assumed spawn(command, :out=>["log", "w", 0600]) spawn(command, :out=>["log", File::APPEND | File::CREAT, 0600])
The array is a [filename, open_mode, perms] tuple. open_mode can be a string or an integer. When open_mode is omitted or nil, File::RDONLY is assumed. The perms element should be an integer. When perms is omitted or nil, 0644 is assumed.
The :close It’s possible to direct an fd be closed in the child process. This is important for implementing `popen`-style logic and other forms of IPC between processes using `IO.pipe`:
rd, wr = IO.pipe pid = spawn('echo', 'hello world', rd => :close, :stdout => wr) wr.close output = rd.read Process.wait(pid)
The POSIX::Spawn#spawn method uses the best available implementation given the current platform and Ruby version. In order of preference, they are:
1. The posix_spawn based C extension method (pspawn). 2. Process::spawn when available (Ruby 1.9 only). 3. A simple pure-Ruby fork/exec based spawn implementation compatible with Ruby >= 1.8.7.
Executes a command in a subshell using the system’s shell interpreter and returns anything written to the new process’s stdout. This method is compatible with Kernel#`.
Returns the String output of the command.
# File lib/posix/spawn.rb, line 272 def `(cmd) r, w = IO.pipe pid = spawn(*system_command_prefixes, cmd, :out => w, r => :close) if pid > 0 w.close out = r.read ::Process.waitpid(pid) out else '' end ensure [r, w].each{ |io| io.close rescue nil } end
Spawn a child process with a variety of options using a pure Ruby fork + exec. Supports the standard spawn interface as described in the POSIX::Spawn module documentation.
# File lib/posix/spawn.rb, line 195 def fspawn(*args) env, argv, options = extract_process_spawn_arguments(*args) valid_options = [:chdir, :unsetenv_others, :pgroup] if badopt = options.find{ |key,val| !fd?(key) && !valid_options.include?(key) } raise ArgumentError, "Invalid option: #{badopt[0].inspect}" elsif !argv.is_a?(Array) || !argv[0].is_a?(Array) || argv[0].size != 2 raise ArgumentError, "Invalid command name" end fork do begin # handle FD => {FD, :close, [file,mode,perms]} options options.each do |key, val| if fd?(key) key = fd_to_io(key) if fd?(val) val = fd_to_io(val) key.reopen(val) key.close_on_exec = false val.close_on_exec = false elsif val == :close if key.respond_to?(:close_on_exec=) key.close_on_exec = true else key.close end elsif val.is_a?(Array) file, mode_string, perms = *val key.reopen(File.open(file, mode_string, perms)) end end end # setup child environment ENV.replace({}) if options[:unsetenv_others] == true env.each { |k, v| ENV[k] = v } # { :chdir => '/' } in options means change into that dir ::Dir.chdir(options[:chdir]) if options[:chdir] # { :pgroup => pgid } options pgroup = options[:pgroup] pgroup = 0 if pgroup == true Process::setpgid(0, pgroup) if pgroup # do the deed ::Kernel::exec(*argv, :close_others=>false) ensure exit!(127) end end end
Spawn a child process with all standard IO streams piped in and out of the spawning process. Supports the standard spawn interface as described in the POSIX::Spawn module documentation.
Returns a [pid, stdin, stdout, stderr] tuple, where pid is the new process’s pid, stdin is a writeable IO object, and stdout / stderr are readable IO objects. The caller should take care to close all IO objects when finished and the child process’s status must be collected by a call to Process::waitpid or equivalent.
# File lib/posix/spawn.rb, line 297 def popen4(*argv) # create some pipes (see pipe(2) manual -- the ruby docs suck) ird, iwr = IO.pipe ord, owr = IO.pipe erd, ewr = IO.pipe # spawn the child process with either end of pipes hooked together opts = ((argv.pop if argv[-1].is_a?(Hash)) || {}).merge( # redirect fds # close other sides :in => ird, iwr => :close, :out => owr, ord => :close, :err => ewr, erd => :close ) pid = spawn(*(argv + [opts])) [pid, iwr, ord, erd] ensure # we're in the parent, close child-side fds [ird, owr, ewr].each { |fd| fd.close if fd } end
Spawn a child process with a variety of options using the posix_spawn(2) systems interfaces. Supports the standard spawn interface as described in the POSIX::Spawn module documentation.
Raises NotImplementedError when the posix_spawn_ext module could not be loaded due to lack of platform support.
# File lib/posix/spawn.rb, line 176 def pspawn(*args) env, argv, options = extract_process_spawn_arguments(*args) raise NotImplementedError unless respond_to?(:_pspawn) if defined? JRUBY_VERSION # On the JVM, changes made to the environment are not propagated down # to C via get/setenv, so we have to fake it here. unless options[:unsetenv_others] == true env = ENV.merge(env) options[:unsetenv_others] = true end end _pspawn(env, argv, options) end
Spawn a child process with a variety of options using the best available implementation for the current platform and Ruby version.
spawn(, command, [argv1, ...], [options])
env - Optional hash specifying the new process’s environment. command - A string command name, or shell program, used to determine the
program to execute.
argvN - Zero or more string program arguments (argv). options - Optional hash of operations to perform before executing the
new child process.
Returns the integer pid of the newly spawned process.
Raises any number of Errno |
exceptions on failure. |
# File lib/posix/spawn.rb, line 160 def spawn(*args) if respond_to?(:_pspawn) pspawn(*args) elsif ::Process.respond_to?(:spawn) ::Process::spawn(*args) else fspawn(*args) end end
Executes a command and waits for it to complete. The command’s exit status is available as $?. Supports the standard spawn interface as described in the POSIX::Spawn module documentation.
This method is compatible with Kernel#system.
Returns true if the command returns a zero exit status, or false for non-zero exit.
# File lib/posix/spawn.rb, line 258 def system(*args) pid = spawn(*args) return false if pid <= 0 ::Process.waitpid(pid) $?.exitstatus == 0 rescue Errno::ENOENT false end
Generated with the Darkfish Rdoc Generator 2.