Ensures any raised {NoSuchDependencyError} has its {NoSuchDependencyError#required_by} set. @yield
Replaces the current process by running the given external command, which can take one of the following forms:
exec(commandline)
command line string which is passed to the standard shell
exec(cmdname, arg1, ...)
command name and one or more arguments (no shell)
exec([cmdname, argv0], arg1, ...)
command name, argv and zero or more arguments (no shell)
In the first form, the string is taken as a command line that is subject to shell expansion before being executed.
The standard shell always means "/bin/sh" on Unix-like systems, same as ENV["RUBYSHELL"] (or ENV["COMSPEC"] on Windows NT series), and similar.
If the string from the first form (exec("command")) follows these simple rules:
no meta characters
no shell reserved word and no special built-in
Ruby invokes the command directly without shell
You can force shell invocation by adding “;” to the string (because “;” is a meta character).
Note that this behavior is observable by pid obtained (return value of spawn() and IO#pid for IO.popen) is the pid of the invoked command, not shell.
In the second form (exec("command1", "arg1", ...)), the first is taken as a command name and the rest are passed as parameters to command with no shell expansion.
In the third form (exec(["command", "argv0"], "arg1", ...)), starting a two-element array at the beginning of the command, the first element is the command to be executed, and the second argument is used as the argv[0] value, which may show up in process listings.
In order to execute the command, one of the exec(2) system calls are used, so the running command may inherit some of the environment of the original program (including open file descriptors).
This behavior is modified by the given env and options parameters. See ::spawn for details.
If the command fails to execute (typically Errno::ENOENT when it was not found) a SystemCallError exception is raised.
This method modifies process attributes according to given options before exec(2) system call. See ::spawn for more details about the given options.
The modified attributes may be retained when exec(2) system call fails.
For example, hard resource limits are not restorable.
Consider to create a child process using ::spawn or Kernel#system if this is not acceptable.
exec "echo *" # echoes list of files in current directory # never get here exec "echo", "*" # echoes an asterisk # never get here
Creates a subprocess. If a block is specified, that block is run in the subprocess, and the subprocess terminates with a status of zero. Otherwise, the fork call returns twice, once in the parent, returning the process ID of the child, and once in the child, returning nil. The child process can exit using Kernel.exit! to avoid running any at_exit functions. The parent process should use Process.wait to collect the termination statuses of its children or use Process.detach to register disinterest in their status; otherwise, the operating system may accumulate zombie processes.
The thread calling fork is the only thread in the created child process. fork doesn’t copy other threads.
If fork is not usable, Process.respond_to?(:fork) returns false.
Note that fork(2) is not available on some platforms like Windows and NetBSD 4. Therefore you should use spawn() instead of fork().
spawn executes specified command and return its pid.
pid = spawn("tar xf ruby-2.0.0-p195.tar.bz2") Process.wait pid pid = spawn(RbConfig.ruby, "-eputs'Hello, world!'") Process.wait pid
This method is similar to Kernel#system but it doesn’t wait for the command to finish.
The parent process should use Process.wait to collect the termination status of its child or use Process.detach to register disinterest in their status; otherwise, the operating system may accumulate zombie processes.
spawn has bunch of options to specify process attributes:
env: hash
name => val : set the environment variable
name => nil : unset the environment variable
the keys and the values except for +nil+ must be strings.
command...:
commandline : command line string which is passed to the standard shell
cmdname, arg1, ... : command name and one or more arguments (This form does not use the shell. See below for caveats.)
[cmdname, argv0], arg1, ... : command name, argv[0] and zero or more arguments (no shell)
options: hash
clearing environment variables:
:unsetenv_others => true : clear environment variables except specified by env
:unsetenv_others => false : don't clear (default)
process group:
:pgroup => true or 0 : make a new process group
:pgroup => pgid : join the specified process group
:pgroup => nil : don't change the process group (default)
create new process group: Windows only
:new_pgroup => true : the new process is the root process of a new process group
:new_pgroup => false : don't create a new process group (default)
resource limit: resourcename is core, cpu, data, etc. See Process.setrlimit.
:rlimit_resourcename => limit
:rlimit_resourcename => [cur_limit, max_limit]
umask:
:umask => int
redirection:
key:
FD : single file descriptor in child process
[FD, FD, ...] : multiple file descriptor in child process
value:
FD : redirect to the file descriptor in parent process
string : redirect to file with open(string, "r" or "w")
[string] : redirect to file with open(string, File::RDONLY)
[string, open_mode] : redirect to file with open(string, open_mode, 0644)
[string, open_mode, perm] : redirect to file with open(string, open_mode, perm)
[:child, FD] : redirect to the redirected file descriptor
:close : close the file descriptor in child process
FD is one of follows
:in : the file descriptor 0 which is the standard input
:out : the file descriptor 1 which is the standard output
:err : the file descriptor 2 which is the standard error
integer : the file descriptor of specified the integer
io : the file descriptor specified as io.fileno
file descriptor inheritance: close non-redirected non-standard fds (3, 4, 5, ...) or not
:close_others => false : inherit
current directory:
:chdir => str
The 'cmdname, arg1, ...' form does not use the shell. However,
on different OSes, different things are provided as built-in
commands. An example of this is 'echo', which is a built-in
on Windows, but is a normal program on Linux and Mac OS X.
This means that `Process.spawn 'echo', '%Path%'` will display
the contents of the `%Path%` environment variable on Windows,
but `Process.spawn 'echo', '$PATH'` prints the literal '$PATH'.
If a hash is given as env, the environment is updated by env before exec(2) in the child process. If a pair in env has nil as the value, the variable is deleted.
# set FOO as BAR and unset BAZ. pid = spawn({"FOO"=>"BAR", "BAZ"=>nil}, command)
If a hash is given as options, it specifies process group, create new process group, resource limit, current directory, umask and redirects for the child process. Also, it can be specified to clear environment variables.
The :unsetenv_others key in options specifies to clear environment variables, other than specified by env.
pid = spawn(command, :unsetenv_others=>true) # no environment variable pid = spawn({"FOO"=>"BAR"}, command, :unsetenv_others=>true) # FOO only
The :pgroup key in options specifies a process group. The corresponding value should be true, zero, a positive integer, or nil. true and zero cause the process to be a process leader of a new process group. A non-zero positive integer causes the process to join the provided process group. The default value, nil, causes the process to remain in the same process group.
pid = spawn(command, :pgroup=>true) # process leader pid = spawn(command, :pgroup=>10) # belongs to the process group 10
The :new_pgroup key in options specifies to pass CREATE_NEW_PROCESS_GROUP flag to CreateProcessW() that is Windows API. This option is only for Windows. true means the new process is the root process of the new process group. The new process has CTRL+C disabled. This flag is necessary for Process.kill(:SIGINT, pid) on the subprocess. :new_pgroup is false by default.
pid = spawn(command, :new_pgroup=>true) # new process group pid = spawn(command, :new_pgroup=>false) # same process group
The :rlimit_foo key specifies a resource limit. foo should be one of resource types such as core. The corresponding value should be an integer or an array which have one or two integers: same as cur_limit and max_limit arguments for Process.setrlimit.
cur, max = Process.getrlimit(:CORE) pid = spawn(command, :rlimit_core=>[0,max]) # disable core temporary. pid = spawn(command, :rlimit_core=>max) # enable core dump pid = spawn(command, :rlimit_core=>0) # never dump core.
The :umask key in options specifies the umask.
pid = spawn(command, :umask=>077)
The :in, :out, :err, an integer, an IO and an array key specifies a redirection. The redirection maps a file descriptor in the child process.
For example, stderr can be merged into stdout as follows:
pid = spawn(command, :err=>:out) pid = spawn(command, 2=>1) pid = spawn(command, STDERR=>:out) pid = spawn(command, STDERR=>STDOUT)
The hash keys specifies a file descriptor in the child process started by spawn. :err, 2 and STDERR specifies the standard error stream (stderr).
The hash values specifies a file descriptor in the parent process which invokes spawn. :out, 1 and STDOUT specifies the standard output stream (stdout).
In the above example, the standard output in the child process is not specified. So it is inherited from the parent process.
The standard input stream (stdin) can be specified by :in, 0 and STDIN.
A filename can be specified as a hash value.
pid = spawn(command, :in=>"/dev/null") # read mode pid = spawn(command, :out=>"/dev/null") # write mode pid = spawn(command, :err=>"log") # write mode pid = spawn(command, [:out, :err]=>"/dev/null") # write mode pid = spawn(command, 3=>"/dev/null") # read mode
For stdout and stderr (and combination of them), it is opened in write mode. Otherwise read mode is used.
For specifying flags and permission of file creation explicitly, an array is used instead.
pid = spawn(command, :in=>["file"]) # read mode is assumed pid = spawn(command, :in=>["file", "r"]) pid = spawn(command, :out=>["log", "w"]) # 0644 assumed pid = spawn(command, :out=>["log", "w", 0600]) pid = spawn(command, :out=>["log", File::WRONLY|File::EXCL|File::CREAT, 0600])
The array specifies a filename, flags and permission. The flags can be a string or an integer. If the flags is omitted or nil, File::RDONLY is assumed. The permission should be an integer. If the permission is omitted or nil, 0644 is assumed.
If an array of IOs and integers are specified as a hash key, all the elements are redirected.
# stdout and stderr is redirected to log file. # The file "log" is opened just once. pid = spawn(command, [:out, :err]=>["log", "w"])
Another way to merge multiple file descriptors is [:child, fd]. [:child, fd] means the file descriptor in the child process. This is different from fd. For example, :err=>:out means redirecting child stderr to parent stdout. But :err=>[:child, :out] means redirecting child stderr to child stdout. They differ if stdout is redirected in the child process as follows.
# stdout and stderr is redirected to log file. # The file "log" is opened just once. pid = spawn(command, :out=>["log", "w"], :err=>[:child, :out])
[:child, :out] can be used to merge stderr into stdout in IO.popen. In this case, IO.popen redirects stdout to a pipe in the child process and [:child, :out] refers the redirected stdout.
io = IO.popen(["sh", "-c", "echo out; echo err >&2", :err=>[:child, :out]]) p io.read #=> "out\nerr\n"
The :chdir key in options specifies the current directory.
pid = spawn(command, :chdir=>"/var/tmp")
spawn closes all non-standard unspecified descriptors by default. The “standard” descriptors are 0, 1 and 2. This behavior is specified by :close_others option. :close_others doesn’t affect the standard descriptors which are closed only if :close is specified explicitly.
pid = spawn(command, :close_others=>true) # close 3,4,5,... (default) pid = spawn(command, :close_others=>false) # don't close 3,4,5,...
:close_others is false by default for spawn and IO.popen.
Note that fds which close-on-exec flag is already set are closed regardless of :close_others option.
So IO.pipe and spawn can be used as IO.popen.
# similar to r = IO.popen(command) r, w = IO.pipe pid = spawn(command, :out=>w) # r, w is closed in the child process. w.close
:close is specified as a hash value to close a fd individually.
f = open(foo) system(command, f=>:close) # don't inherit f.
If a file descriptor need to be inherited, io=>io can be used.
# valgrind has --log-fd option for log destination. # log_w=>log_w indicates log_w.fileno inherits to child process. log_r, log_w = IO.pipe pid = spawn("valgrind", "--log-fd=#{log_w.fileno}", "echo", "a", log_w=>log_w) log_w.close p log_r.read
It is also possible to exchange file descriptors.
pid = spawn(command, :out=>:err, :err=>:out)
The hash keys specify file descriptors in the child process. The hash values specifies file descriptors in the parent process. So the above specifies exchanging stdout and stderr. Internally, spawn uses an extra file descriptor to resolve such cyclic file descriptor mapping.
See Kernel.exec for the standard shell.
Exits the process immediately. No exit handlers are run. status is returned to the underlying system as the exit status.
Process.exit!(true)
Initiates the termination of the Ruby script by raising the SystemExit exception. This exception may be caught. The optional parameter is used to return a status code to the invoking environment. true and FALSE of status means success and failure respectively. The interpretation of other integer values are system dependent.
begin exit puts "never get here" rescue SystemExit puts "rescued a SystemExit exception" end puts "after begin block"
produces:
rescued a SystemExit exception after begin block
Just prior to termination, Ruby executes any at_exit functions (see Kernel::at_exit) and runs any object finalizers (see ObjectSpace::define_finalizer).
at_exit { puts "at_exit function" } ObjectSpace.define_finalizer("string", proc { puts "in finalizer" }) exit
produces:
at_exit function in finalizer
Terminate execution immediately, effectively by calling Kernel.exit(false). If msg is given, it is written to STDERR prior to terminating.
Returns the status of the last executed child process in the current thread.
Process.wait Process.spawn("ruby", "-e", "exit 13") Process.last_status #=> #<Process::Status: pid 4825 exit 13>
If no child process has ever been executed in the current thread, this returns nil.
Process.last_status #=> nil
Sends the given signal to the specified process id(s) if pid is positive. If pid is zero signal is sent to all processes whose group ID is equal to the group ID of the process. signal may be an integer signal number or a POSIX signal name (either with or without a SIG prefix). If signal is negative (or starts with a minus sign), kills process groups instead of processes. Not all signals are available on all platforms. The keys and values of Signal.list are known signal names and numbers, respectively.
pid = fork do Signal.trap("HUP") { puts "Ouch!"; exit } # ... do some work ... end # ... Process.kill("HUP", pid) Process.wait
produces:
Ouch!
If signal is an integer but wrong for signal, Errno::EINVAL or RangeError will be raised. Otherwise unless signal is a String or a Symbol, and a known signal name, ArgumentError will be raised.
Also, Errno::ESRCH or RangeError for invalid pid, Errno::EPERM when failed because of no privilege, will be raised. In these cases, signals may have been sent to preceding processes.
Waits for a child process to exit, returns its process id, and sets $? to a Process::Status object containing information on that process. Which child it waits on depends on the value of pid:
Waits for the child whose process ID equals pid.
Waits for any child whose process group ID equals that of the calling process.
Waits for any child process (the default if no pid is given).
Waits for any child whose process group ID equals the absolute value of pid.
The flags argument may be a logical or of the flag values Process::WNOHANG (do not block if no child available) or Process::WUNTRACED (return stopped children that haven’t been reported). Not all flags are available on all platforms, but a flag value of zero will work on all platforms.
Calling this method raises a SystemCallError if there are no child processes. Not available on all platforms.
include Process fork { exit 99 } #=> 27429 wait #=> 27429 $?.exitstatus #=> 99 pid = fork { sleep 3 } #=> 27440 Time.now #=> 2008-03-08 19:56:16 +0900 waitpid(pid, Process::WNOHANG) #=> nil Time.now #=> 2008-03-08 19:56:16 +0900 waitpid(pid, 0) #=> 27440 Time.now #=> 2008-03-08 19:56:19 +0900
Waits for a child process to exit (see Process::waitpid for exact semantics) and returns an array containing the process id and the exit status (a Process::Status object) of that child. Raises a SystemCallError if there are no child processes.
Process.fork { exit 99 } #=> 27437 pid, status = Process.wait2 pid #=> 27437 status.exitstatus #=> 99
Waits for a child process to exit, returns its process id, and sets $? to a Process::Status object containing information on that process. Which child it waits on depends on the value of pid:
Waits for the child whose process ID equals pid.
Waits for any child whose process group ID equals that of the calling process.
Waits for any child process (the default if no pid is given).
Waits for any child whose process group ID equals the absolute value of pid.
The flags argument may be a logical or of the flag values Process::WNOHANG (do not block if no child available) or Process::WUNTRACED (return stopped children that haven’t been reported). Not all flags are available on all platforms, but a flag value of zero will work on all platforms.
Calling this method raises a SystemCallError if there are no child processes. Not available on all platforms.
include Process fork { exit 99 } #=> 27429 wait #=> 27429 $?.exitstatus #=> 99 pid = fork { sleep 3 } #=> 27440 Time.now #=> 2008-03-08 19:56:16 +0900 waitpid(pid, Process::WNOHANG) #=> nil Time.now #=> 2008-03-08 19:56:16 +0900 waitpid(pid, 0) #=> 27440 Time.now #=> 2008-03-08 19:56:19 +0900
Waits for a child process to exit (see Process::waitpid for exact semantics) and returns an array containing the process id and the exit status (a Process::Status object) of that child. Raises a SystemCallError if there are no child processes.
Process.fork { exit 99 } #=> 27437 pid, status = Process.wait2 pid #=> 27437 status.exitstatus #=> 99
Waits for all children, returning an array of pid/status pairs (where status is a Process::Status object).
fork { sleep 0.2; exit 2 } #=> 27432 fork { sleep 0.1; exit 1 } #=> 27433 fork { exit 0 } #=> 27434 p Process.waitall
produces:
[[30982, #<Process::Status: pid 30982 exit 0>], [30979, #<Process::Status: pid 30979 exit 1>], [30976, #<Process::Status: pid 30976 exit 2>]]
Some operating systems retain the status of terminated child processes until the parent collects that status (normally using some variant of wait()). If the parent never collects this status, the child stays around as a zombie process. Process::detach prevents this by setting up a separate Ruby thread whose sole job is to reap the status of the process pid when it terminates. Use detach only when you do not intend to explicitly wait for the child to terminate.
The waiting thread returns the exit status of the detached process when it terminates, so you can use Thread#join to know the result. If specified pid is not a valid child process ID, the thread returns nil immediately.
The waiting thread has pid method which returns the pid.
In this first example, we don’t reap the first child process, so it appears as a zombie in the process status display.
p1 = fork { sleep 0.1 } p2 = fork { sleep 0.2 } Process.waitpid(p2) sleep 2 system("ps -ho pid,state -p #{p1}")
produces:
27389 Z
In the next example, Process::detach is used to reap the child automatically.
p1 = fork { sleep 0.1 } p2 = fork { sleep 0.2 } Process.detach(p1) Process.waitpid(p2) sleep 2 system("ps -ho pid,state -p #{p1}")
(produces no output)
Returns the process id of this process. Not available on all platforms.
Process.pid #=> 27415
Returns the process id of the parent of this process. Returns untrustworthy value on Win32/64. Not available on all platforms.
puts "I am #{Process.pid}" Process.fork { puts "Dad is #{Process.ppid}" }
produces:
I am 27417 Dad is 27417
Returns the process group ID for this process. Not available on all platforms.
Process.getpgid(0) #=> 25527 Process.getpgrp #=> 25527
Equivalent to setpgid(0,0). Not available on all platforms.
Returns the process group ID for the given process id. Not available on all platforms.
Process.getpgid(Process.ppid()) #=> 25527
Sets the process group ID of pid (0 indicates this process) to integer. Not available on all platforms.
Returns the session ID for the given process id. If not given, return current process sid. Not available on all platforms.
Process.getsid() #=> 27422 Process.getsid(0) #=> 27422 Process.getsid(Process.pid()) #=> 27422
Establishes this process as a new session and process group leader, with no controlling tty. Returns the session id. Not available on all platforms.
Process.setsid #=> 27422