module PTY - Documentation for Ruby 4.0
Description: module PTY: Creates and manages pseudo terminals (PTYs). en.
Keywords: ruby,module,PTY

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# module PTY

Creates and manages pseudo terminals (PTYs). See also en.wikipedia.org/wiki/Pseudo_terminal

`PTY` allows you to allocate new terminals using `::open` or `::spawn` a new terminal with a specific command.

## Example

In this example we will change the buffering type in the `factor` command, assuming that factor uses stdio for stdout buffering.

If `IO.pipe` is used instead of `PTY.open`, this code deadlocks because factor’s stdout is fully buffered.

    # start by requiring the standard library PTY
    require 'pty'

    master, slave = PTY.open
    read, write = IO.pipe
    pid = spawn("factor", :in=>read, :out=>slave)
    read.close     # we dont need the read
    slave.close    # or the slave

    # pipe "42" to the factor command
    write.puts "42"
    # output the response from factor
    p master.gets #=> "42: 2 3 7\n"

    # pipe "144" to factor and print out the response
    write.puts "144"
    p master.gets #=> "144: 2 2 2 2 3 3\n"
    write.close # close the pipe

    # The result of read operation when pty slave is closed is platform
    # dependent.
    ret = begin
            master.gets     # FreeBSD returns nil.
          rescue Errno::EIO # GNU/Linux raises EIO.
            nil
          end
    p ret #=> nil

## License

© Copyright 1998 by Akinori Ito.

This software may be redistributed freely for this purpose, in full or in part, provided that this entire copyright notice is included on any copies of this software and applications and derivations thereof.

This software is provided on an “as is” basis, without warranty of any kind, either expressed or implied, as to any matter including, but not limited to warranty of fitness of purpose, or merchantability, or results obtained from use of this software.

### Public Class Methods

check(pid, raise = false) → Process::Status or nil
check(pid, true) → nil or raises PTY::ChildExited
Source

    static VALUE
    pty_check(int argc, VALUE *argv, VALUE self)
    {
        VALUE pid, exc;
        rb_pid_t cpid;
        int status;
        const int flag =
    #ifdef WNOHANG
            WNOHANG|
    #endif
    #ifdef WUNTRACED
            WUNTRACED|
    #endif
            0;

        rb_scan_args(argc, argv, "11", &pid, &exc);
        cpid = rb_waitpid(NUM2PIDT(pid), &status, flag);
        if (cpid == -1 || cpid == 0) return Qnil;

        if (!RTEST(exc)) return rb_last_status_get();
        raise_from_check(cpid, status);

        UNREACHABLE_RETURN(Qnil);
    }

Checks the status of the child process specified by `pid`. Returns `nil` if the process is still alive.

If the process is not alive, and `raise` was true, a `PTY::ChildExited` exception will be raised. Otherwise it will return a `Process::Status` instance.

`pid`

  The process id of the process to check

`raise`

  If `true` and the process identified by `pid` is no longer alive a `PTY::ChildExited` is raised.

getpty
Alias for: spawn
open → [master_io, slave_file]
open {|(master_io, slave_file)| ... } → block value
Source

    static VALUE
    pty_open(VALUE klass)
    {
        int master_fd, slave_fd;
        char slavename[DEVICELEN];

        getDevice(&master_fd, &slave_fd, slavename, 1);

        VALUE master_path = rb_obj_freeze(rb_sprintf("masterpty:%s", slavename));
        VALUE master_io = rb_io_open_descriptor(rb_cIO, master_fd, FMODE_READWRITE | FMODE_SYNC | FMODE_DUPLEX, master_path, RUBY_IO_TIMEOUT_DEFAULT, NULL);

        VALUE slave_path = rb_obj_freeze(rb_str_new_cstr(slavename));
        VALUE slave_file = rb_io_open_descriptor(rb_cFile, slave_fd, FMODE_READWRITE | FMODE_SYNC | FMODE_DUPLEX | FMODE_TTY, slave_path, RUBY_IO_TIMEOUT_DEFAULT, NULL);

        VALUE assoc = rb_assoc_new(master_io, slave_file);

        if (rb_block_given_p()) {
            return rb_ensure(rb_yield, assoc, pty_close_pty, assoc);
        }

        return assoc;
    }

Allocates a pty (pseudo-terminal).

In the block form, yields an array of two elements (`master_io, slave_file`) and the value of the block is returned from `open`.

The `IO` and `File` are both closed after the block completes if they haven’t been already closed.

    PTY.open {|master, slave|
      p master      #=> #<IO:masterpty:/dev/pts/1>
      p slave      #=> #<File:/dev/pts/1>
      p slave.path #=> "/dev/pts/1"
    }

In the non-block form, returns a two element array, `[master_io, slave_file]`.

    master, slave = PTY.open
    # do something with master for IO, or the slave file

The arguments in both forms are:

`master_io`

  the master of the pty, as an `IO`.

`slave_file`

  the slave of the pty, as a `File`. The path to the terminal device is available via `slave_file.path`

`IO#raw!` is usable to disable newline conversions:

    require 'io/console'
    PTY.open {|m, s|
      s.raw!
      # ...
    }

spawn([env,] command_line) { |r, w, pid| ... }
spawn([env,] command_line) → [r, w, pid]
spawn([env,] command, arguments, ...) { |r, w, pid| ... }
spawn([env,] command, arguments, ...) → [r, w, pid]
Source

    static VALUE
    pty_getpty(int argc, VALUE *argv, VALUE self)
    {
        VALUE res;
        struct pty_info info;
        char SlaveName[DEVICELEN];

        establishShell(argc, argv, &info, SlaveName);

        VALUE pty_path = rb_obj_freeze(rb_str_new_cstr(SlaveName));
        VALUE rport = rb_io_open_descriptor(
            rb_cFile, info.fd, FMODE_READABLE, pty_path, RUBY_IO_TIMEOUT_DEFAULT, NULL
        );

        int wpty_fd = rb_cloexec_dup(info.fd);
        if (wpty_fd == -1) {
            rb_sys_fail("dup()");
        }
        VALUE wport = rb_io_open_descriptor(
            rb_cFile, wpty_fd, FMODE_WRITABLE | FMODE_TRUNC | FMODE_CREATE | FMODE_SYNC,
            pty_path, RUBY_IO_TIMEOUT_DEFAULT, NULL
        );

        res = rb_ary_new2(3);
        rb_ary_store(res, 0, rport);
        rb_ary_store(res, 1, wport);
        rb_ary_store(res,2,PIDT2NUM(info.child_pid));

        if (rb_block_given_p()) {
            rb_ensure(rb_yield, res, pty_detach_process, (VALUE)&info);
            return Qnil;
        }
        return res;
    }

Spawns the specified command on a newly allocated pty. You can also use the alias `::getpty`.

The command’s controlling tty is set to the slave device of the pty and its standard input/output/error is redirected to the slave device.

`env` is an optional hash that provides additional environment variables to the spawned pty.

    # sets FOO to "bar"
    PTY.spawn({"FOO"=>"bar"}, "printenv", "FOO") do |r, w, pid|
      p r.read #=> "bar\r\n"
    ensure
      r.close; w.close; Process.wait(pid)
    end
    # unsets FOO
    PTY.spawn({"FOO"=>nil}, "printenv", "FOO") do |r, w, pid|
      p r.read #=> ""
    ensure
      r.close; w.close; Process.wait(pid)
    end

`command` and `command_line` are the full commands to run, given a `String`. Any additional `arguments` will be passed to the command.

### Return values

In the non-block form this returns an array of size three, `[r, w, pid]`.

In the block form these same values will be yielded to the block:

`r`

  A readable `IO` that contains the command’s standard output and standard error

`w`

  A writable `IO` that is the command’s standard input

`pid`

  The process identifier for the command.

### Clean up

This method does not clean up like closing IOs or waiting for child process, except that the process is detached in the block form to prevent it from becoming a zombie (see `Process.detach`). Any other cleanup is the responsibility of the caller. If waiting for `pid`, be sure to close both `r` and `w` before doing so; doing it in the reverse order may cause deadlock on some OSes.

Also aliased as: getpty