Open3

Open3.capture2 captures the standard output of a command.

stdout_str, status = Open3.capture2([env,] cmd... [, opts])

The arguments env, cmd and opts are passed to Open3.popen3 except opts[:stdin_data] and opts[:binmode]. See Process.spawn.

If opts[:stdin_data] is specified, it is sent to the command’s standard input.

If opts[:binmode] is true, internal pipes are set to binary mode.

Example:

# factor is a command for integer factorization.
o, s = Open3.capture2("factor", :stdin_data=>"42")
p o #=> "42: 2 3 7\n"

# generate x**2 graph in png using gnuplot.
gnuplot_commands = <<"End"
  set terminal png
  plot x**2, "-" with lines
  1 14
  2 1
  3 8
  4 5
  e
End
image, s = Open3.capture2("gnuplot", :stdin_data=>gnuplot_commands, :binmode=>true)

Open3.capture2e captures the standard output and the standard error of a command.

stdout_and_stderr_str, status = Open3.capture2e([env,] cmd... [, opts])

The arguments env, cmd and opts are passed to Open3.popen3 except opts[:stdin_data] and opts[:binmode]. See Process.spawn.

If opts[:stdin_data] is specified, it is sent to the command’s standard input.

If opts[:binmode] is true, internal pipes are set to binary mode.

Example:

# capture make log
make_log, s = Open3.capture2e("make")

Open3.capture3 captures the standard output and the standard error of a command.

stdout_str, stderr_str, status = Open3.capture3([env,] cmd... [, opts])

The arguments env, cmd and opts are passed to Open3.popen3 except opts[:stdin_data] and opts[:binmode]. See Process.spawn.

If opts[:stdin_data] is specified, it is sent to the command’s standard input.

If opts[:binmode] is true, internal pipes are set to binary mode.

Examples:

# dot is a command of graphviz.
graph = <<'End'
  digraph g {
    a -> b
  }
End
drawn_graph, dot_log = Open3.capture3("dot -v", :stdin_data=>graph)

o, e, s = Open3.capture3("echo abc; sort >&2", :stdin_data=>"foo\nbar\nbaz\n")
p o #=> "abc\n"
p e #=> "bar\nbaz\nfoo\n"
p s #=> #<Process::Status: pid 32682 exit 0>

# generate a thumbnail image using the convert command of ImageMagick.
# However, if the image is really stored in a file,
# system("convert", "-thumbnail", "80", "png:#{filename}", "png:-") is better
# because of reduced memory consumption.
# But if the image is stored in a DB or generated by the gnuplot Open3.capture2 example,
# Open3.capture3 should be considered.
#
image = File.read("/usr/share/openclipart/png/animals/mammals/sheep-md-v0.1.png", :binmode=>true)
thumbnail, err, s = Open3.capture3("convert -thumbnail 80 png:- png:-", :stdin_data=>image, :binmode=>true)
if s.success?
  STDOUT.binmode; print thumbnail
end

Open3.pipeline starts a list of commands as a pipeline. It waits for the completion of the commands. No pipes are created for stdin of the first command and stdout of the last command.

status_list = Open3.pipeline(cmd1, cmd2, ... [, opts])

Each cmd is a string or an array. If it is an array, the elements are passed to Process.spawn.

cmd:
  commandline                              command line string which is passed to a shell
  [env, commandline, opts]                 command line string which is passed to a shell
  [env, cmdname, arg1, ..., opts]          command name and one or more arguments (no shell)
  [env, [cmdname, argv0], arg1, ..., opts] command name and arguments including argv[0] (no shell)

Note that env and opts are optional, as Process.spawn.

Example:

fname = "/usr/share/man/man1/ruby.1.gz"
p Open3.pipeline(["zcat", fname], "nroff -man", "less")
#=> [#<Process::Status: pid 11817 exit 0>,
#    #<Process::Status: pid 11820 exit 0>,
#    #<Process::Status: pid 11828 exit 0>]

fname = "/usr/share/man/man1/ls.1.gz"
Open3.pipeline(["zcat", fname], "nroff -man", "colcrt")

# convert PDF to PS and send to a printer by lpr
pdf_file = "paper.pdf"
printer = "printer-name"
Open3.pipeline(["pdftops", pdf_file, "-"],
               ["lpr", "-P#{printer}"])

# count lines
Open3.pipeline("sort", "uniq -c", :in=>"names.txt", :out=>"count")

# cyclic pipeline
r,w = IO.pipe
w.print "ibase=14\n10\n"
Open3.pipeline("bc", "tee /dev/tty", :in=>r, :out=>w)
#=> 14
#   18
#   22
#   30
#   42
#   58
#   78
#   106
#   202

Open3.pipeline_r starts a list of commands as a pipeline with a pipe which connects to stdout of the last command.

Open3.pipeline_r(cmd1, cmd2, ... [, opts]) {|last_stdout, wait_threads|
  ...
}

last_stdout, wait_threads = Open3.pipeline_r(cmd1, cmd2, ... [, opts])
...
last_stdout.close

Each cmd is a string or an array. If it is an array, the elements are passed to Process.spawn.

cmd:
  commandline                              command line string which is passed to a shell
  [env, commandline, opts]                 command line string which is passed to a shell
  [env, cmdname, arg1, ..., opts]          command name and one or more arguments (no shell)
  [env, [cmdname, argv0], arg1, ..., opts] command name and arguments including argv[0] (no shell)

Note that env and opts are optional, as for Process.spawn.

Example:

Open3.pipeline_r("zcat /var/log/apache2/access.log.*.gz",
                 [{"LANG"=>"C"}, "grep", "GET /favicon.ico"],
                 "logresolve") {|o, ts|
  o.each_line {|line|
    ...
  }
}

Open3.pipeline_r("yes", "head -10") {|o, ts|
  p o.read      #=> "y\ny\ny\ny\ny\ny\ny\ny\ny\ny\n"
  p ts[0].value #=> #<Process::Status: pid 24910 SIGPIPE (signal 13)>
  p ts[1].value #=> #<Process::Status: pid 24913 exit 0>
}

Open3.pipeline_rw starts a list of commands as a pipeline with pipes which connect to stdin of the first command and stdout of the last command.

Open3.pipeline_rw(cmd1, cmd2, ... [, opts]) {|first_stdin, last_stdout, wait_threads|
  ...
}

first_stdin, last_stdout, wait_threads = Open3.pipeline_rw(cmd1, cmd2, ... [, opts])
...
first_stdin.close
last_stdout.close

Each cmd is a string or an array. If it is an array, the elements are passed to Process.spawn.

cmd:
  commandline                              command line string which is passed to a shell
  [env, commandline, opts]                 command line string which is passed to a shell
  [env, cmdname, arg1, ..., opts]          command name and one or more arguments (no shell)
  [env, [cmdname, argv0], arg1, ..., opts] command name and arguments including argv[0] (no shell)

Note that env and opts are optional, as for Process.spawn.

The options to pass to Process.spawn are constructed by merging opts, the last hash element of the array, and specifications for the pipes between each of the commands.

Example:

Open3.pipeline_rw("tr -dc A-Za-z", "wc -c") {|i, o, ts|
  i.puts "All persons more than a mile high to leave the court."
  i.close
  p o.gets #=> "42\n"
}

Open3.pipeline_rw("sort", "cat -n") {|stdin, stdout, wait_thrs|
  stdin.puts "foo"
  stdin.puts "bar"
  stdin.puts "baz"
  stdin.close     # send EOF to sort.
  p stdout.read   #=> "     1\tbar\n     2\tbaz\n     3\tfoo\n"
}

Open3.pipeline_start starts a list of commands as a pipeline. No pipes are created for stdin of the first command and stdout of the last command.

Open3.pipeline_start(cmd1, cmd2, ... [, opts]) {|wait_threads|
  ...
}

wait_threads = Open3.pipeline_start(cmd1, cmd2, ... [, opts])
...

Each cmd is a string or an array. If it is an array, the elements are passed to Process.spawn.

cmd:
  commandline                              command line string which is passed to a shell
  [env, commandline, opts]                 command line string which is passed to a shell
  [env, cmdname, arg1, ..., opts]          command name and one or more arguments (no shell)
  [env, [cmdname, argv0], arg1, ..., opts] command name and arguments including argv[0] (no shell)

Note that env and opts are optional, as for Process.spawn.

Example:

# Run xeyes in 10 seconds.
Open3.pipeline_start("xeyes") {|ts|
  sleep 10
  t = ts[0]
  Process.kill("TERM", t.pid)
  p t.value #=> #<Process::Status: pid 911 SIGTERM (signal 15)>
}

# Convert pdf to ps and send it to a printer.
# Collect error message of pdftops and lpr.
pdf_file = "paper.pdf"
printer = "printer-name"
err_r, err_w = IO.pipe
Open3.pipeline_start(["pdftops", pdf_file, "-"],
                     ["lpr", "-P#{printer}"],
                     :err=>err_w) {|ts|
  err_w.close
  p err_r.read # error messages of pdftops and lpr.
}

Open3.pipeline_w starts a list of commands as a pipeline with a pipe which connects to stdin of the first command.

Open3.pipeline_w(cmd1, cmd2, ... [, opts]) {|first_stdin, wait_threads|
  ...
}

first_stdin, wait_threads = Open3.pipeline_w(cmd1, cmd2, ... [, opts])
...
first_stdin.close

Each cmd is a string or an array. If it is an array, the elements are passed to Process.spawn.

cmd:
  commandline                              command line string which is passed to a shell
  [env, commandline, opts]                 command line string which is passed to a shell
  [env, cmdname, arg1, ..., opts]          command name and one or more arguments (no shell)
  [env, [cmdname, argv0], arg1, ..., opts] command name and arguments including argv[0] (no shell)

Note that env and opts are optional, as for Process.spawn.

Example:

Open3.pipeline_w("bzip2 -c", :out=>"/tmp/hello.bz2") {|i, ts|
  i.puts "hello"
}

Open3.popen2 is similar to Open3.popen3 except that it doesn’t create a pipe for the standard error stream.

Block form:

Open3.popen2([env,] cmd... [, opts]) {|stdin, stdout, wait_thr|
  pid = wait_thr.pid # pid of the started process.
  ...
  exit_status = wait_thr.value # Process::Status object returned.
}

Non-block form:

stdin, stdout, wait_thr = Open3.popen2([env,] cmd... [, opts])
...
stdin.close  # stdin and stdout should be closed explicitly in this form.
stdout.close

See Process.spawn for the optional hash arguments env and opts.

Example:

Open3.popen2("wc -c") {|i,o,t|
  i.print "answer to life the universe and everything"
  i.close
  p o.gets #=> "42\n"
}

Open3.popen2("bc -q") {|i,o,t|
  i.puts "obase=13"
  i.puts "6 * 9"
  p o.gets #=> "42\n"
}

Open3.popen2("dc") {|i,o,t|
  i.print "42P"
  i.close
  p o.read #=> "*"
}

Open3.popen2e is similar to Open3.popen3 except that it merges the standard output stream and the standard error stream.

Block form:

Open3.popen2e([env,] cmd... [, opts]) {|stdin, stdout_and_stderr, wait_thr|
  pid = wait_thr.pid # pid of the started process.
  ...
  exit_status = wait_thr.value # Process::Status object returned.
}

Non-block form:

stdin, stdout_and_stderr, wait_thr = Open3.popen2e([env,] cmd... [, opts])
...
stdin.close  # stdin and stdout_and_stderr should be closed explicitly in this form.
stdout_and_stderr.close

See Process.spawn for the optional hash arguments env and opts.

Example:

# check gcc warnings
source = "foo.c"
Open3.popen2e("gcc", "-Wall", source) {|i,oe,t|
  oe.each {|line|
    if /warning/ =~ line
      ...
    end
  }
}

Open stdin, stdout, and stderr streams and start external executable. In addition, a thread to wait for the started process is created. The thread has a pid method and a thread variable :pid which is the pid of the started process.

Block form:

Open3.popen3([env,] cmd... [, opts]) {|stdin, stdout, stderr, wait_thr|
  pid = wait_thr.pid # pid of the started process.
  ...
  exit_status = wait_thr.value # Process::Status object returned.
}

Non-block form:

stdin, stdout, stderr, wait_thr = Open3.popen3([env,] cmd... [, opts])
pid = wait_thr[:pid]  # pid of the started process
...
stdin.close  # stdin, stdout and stderr should be closed explicitly in this form.
stdout.close
stderr.close
exit_status = wait_thr.value  # Process::Status object returned.

The parameters env, cmd, and opts are passed to Process.spawn. A commandline string and a list of argument strings can be accepted as follows:

Open3.popen3("echo abc") {|i, o, e, t| ... }
Open3.popen3("echo", "abc") {|i, o, e, t| ... }
Open3.popen3(["echo", "argv0"], "abc") {|i, o, e, t| ... }

If the last parameter, opts, is a Hash, it is recognized as an option for Process.spawn.

Open3.popen3("pwd", :chdir=>"/") {|i,o,e,t|
  p o.read.chomp #=> "/"
}

wait_thr.value waits for the termination of the process. The block form also waits for the process when it returns.

Closing stdin, stdout and stderr does not wait for the process to complete.

You should be careful to avoid deadlocks. Since pipes are fixed length buffers, Open3.popen3(“prog”) {|i, o, e, t| o.read } deadlocks if the program generates too much output on stderr. You should read stdout and stderr simultaneously (using threads or IO.select). However, if you don’t need stderr output, you can use Open3.popen2. If merged stdout and stderr output is not a problem, you can use Open3.popen2e. If you really need stdout and stderr output as separate strings, you can consider Open3.capture3.

Open3.capture2 captures the standard output of a command.

stdout_str, status = Open3.capture2([env,] cmd... [, opts])

The arguments env, cmd and opts are passed to Open3.popen3 except opts[:stdin_data] and opts[:binmode]. See Process.spawn.

If opts[:stdin_data] is specified, it is sent to the command’s standard input.

If opts[:binmode] is true, internal pipes are set to binary mode.

Example:

# factor is a command for integer factorization.
o, s = Open3.capture2("factor", :stdin_data=>"42")
p o #=> "42: 2 3 7\n"

# generate x**2 graph in png using gnuplot.
gnuplot_commands = <<"End"
  set terminal png
  plot x**2, "-" with lines
  1 14
  2 1
  3 8
  4 5
  e
End
image, s = Open3.capture2("gnuplot", :stdin_data=>gnuplot_commands, :binmode=>true)

Open3.capture2e captures the standard output and the standard error of a command.

stdout_and_stderr_str, status = Open3.capture2e([env,] cmd... [, opts])

The arguments env, cmd and opts are passed to Open3.popen3 except opts[:stdin_data] and opts[:binmode]. See Process.spawn.

If opts[:stdin_data] is specified, it is sent to the command’s standard input.

If opts[:binmode] is true, internal pipes are set to binary mode.

Example:

# capture make log
make_log, s = Open3.capture2e("make")

Open3.capture3 captures the standard output and the standard error of a command.

stdout_str, stderr_str, status = Open3.capture3([env,] cmd... [, opts])

The arguments env, cmd and opts are passed to Open3.popen3 except opts[:stdin_data] and opts[:binmode]. See Process.spawn.

If opts[:stdin_data] is specified, it is sent to the command’s standard input.

If opts[:binmode] is true, internal pipes are set to binary mode.

Examples:

# dot is a command of graphviz.
graph = <<'End'
  digraph g {
    a -> b
  }
End
drawn_graph, dot_log = Open3.capture3("dot -v", :stdin_data=>graph)

o, e, s = Open3.capture3("echo abc; sort >&2", :stdin_data=>"foo\nbar\nbaz\n")
p o #=> "abc\n"
p e #=> "bar\nbaz\nfoo\n"
p s #=> #<Process::Status: pid 32682 exit 0>

# generate a thumbnail image using the convert command of ImageMagick.
# However, if the image is really stored in a file,
# system("convert", "-thumbnail", "80", "png:#{filename}", "png:-") is better
# because of reduced memory consumption.
# But if the image is stored in a DB or generated by the gnuplot Open3.capture2 example,
# Open3.capture3 should be considered.
#
image = File.read("/usr/share/openclipart/png/animals/mammals/sheep-md-v0.1.png", :binmode=>true)
thumbnail, err, s = Open3.capture3("convert -thumbnail 80 png:- png:-", :stdin_data=>image, :binmode=>true)
if s.success?
  STDOUT.binmode; print thumbnail
end

Open3.pipeline starts a list of commands as a pipeline. It waits for the completion of the commands. No pipes are created for stdin of the first command and stdout of the last command.

status_list = Open3.pipeline(cmd1, cmd2, ... [, opts])

Each cmd is a string or an array. If it is an array, the elements are passed to Process.spawn.

cmd:
  commandline                              command line string which is passed to a shell
  [env, commandline, opts]                 command line string which is passed to a shell
  [env, cmdname, arg1, ..., opts]          command name and one or more arguments (no shell)
  [env, [cmdname, argv0], arg1, ..., opts] command name and arguments including argv[0] (no shell)

Note that env and opts are optional, as Process.spawn.

Example:

fname = "/usr/share/man/man1/ruby.1.gz"
p Open3.pipeline(["zcat", fname], "nroff -man", "less")
#=> [#<Process::Status: pid 11817 exit 0>,
#    #<Process::Status: pid 11820 exit 0>,
#    #<Process::Status: pid 11828 exit 0>]

fname = "/usr/share/man/man1/ls.1.gz"
Open3.pipeline(["zcat", fname], "nroff -man", "colcrt")

# convert PDF to PS and send to a printer by lpr
pdf_file = "paper.pdf"
printer = "printer-name"
Open3.pipeline(["pdftops", pdf_file, "-"],
               ["lpr", "-P#{printer}"])

# count lines
Open3.pipeline("sort", "uniq -c", :in=>"names.txt", :out=>"count")

# cyclic pipeline
r,w = IO.pipe
w.print "ibase=14\n10\n"
Open3.pipeline("bc", "tee /dev/tty", :in=>r, :out=>w)
#=> 14
#   18
#   22
#   30
#   42
#   58
#   78
#   106
#   202

Open3.pipeline_r starts a list of commands as a pipeline with a pipe which connects to stdout of the last command.

Open3.pipeline_r(cmd1, cmd2, ... [, opts]) {|last_stdout, wait_threads|
  ...
}

last_stdout, wait_threads = Open3.pipeline_r(cmd1, cmd2, ... [, opts])
...
last_stdout.close

Each cmd is a string or an array. If it is an array, the elements are passed to Process.spawn.

cmd:
  commandline                              command line string which is passed to a shell
  [env, commandline, opts]                 command line string which is passed to a shell
  [env, cmdname, arg1, ..., opts]          command name and one or more arguments (no shell)
  [env, [cmdname, argv0], arg1, ..., opts] command name and arguments including argv[0] (no shell)

Note that env and opts are optional, as for Process.spawn.

Example:

Open3.pipeline_r("zcat /var/log/apache2/access.log.*.gz",
                 [{"LANG"=>"C"}, "grep", "GET /favicon.ico"],
                 "logresolve") {|o, ts|
  o.each_line {|line|
    ...
  }
}

Open3.pipeline_r("yes", "head -10") {|o, ts|
  p o.read      #=> "y\ny\ny\ny\ny\ny\ny\ny\ny\ny\n"
  p ts[0].value #=> #<Process::Status: pid 24910 SIGPIPE (signal 13)>
  p ts[1].value #=> #<Process::Status: pid 24913 exit 0>
}

Open3.pipeline_rw starts a list of commands as a pipeline with pipes which connect to stdin of the first command and stdout of the last command.

Open3.pipeline_rw(cmd1, cmd2, ... [, opts]) {|first_stdin, last_stdout, wait_threads|
  ...
}

first_stdin, last_stdout, wait_threads = Open3.pipeline_rw(cmd1, cmd2, ... [, opts])
...
first_stdin.close
last_stdout.close

Each cmd is a string or an array. If it is an array, the elements are passed to Process.spawn.

cmd:
  commandline                              command line string which is passed to a shell
  [env, commandline, opts]                 command line string which is passed to a shell
  [env, cmdname, arg1, ..., opts]          command name and one or more arguments (no shell)
  [env, [cmdname, argv0], arg1, ..., opts] command name and arguments including argv[0] (no shell)

Note that env and opts are optional, as for Process.spawn.

The options to pass to Process.spawn are constructed by merging opts, the last hash element of the array, and specifications for the pipes between each of the commands.

Example:

Open3.pipeline_rw("tr -dc A-Za-z", "wc -c") {|i, o, ts|
  i.puts "All persons more than a mile high to leave the court."
  i.close
  p o.gets #=> "42\n"
}

Open3.pipeline_rw("sort", "cat -n") {|stdin, stdout, wait_thrs|
  stdin.puts "foo"
  stdin.puts "bar"
  stdin.puts "baz"
  stdin.close     # send EOF to sort.
  p stdout.read   #=> "     1\tbar\n     2\tbaz\n     3\tfoo\n"
}

Open3.pipeline_start starts a list of commands as a pipeline. No pipes are created for stdin of the first command and stdout of the last command.

Open3.pipeline_start(cmd1, cmd2, ... [, opts]) {|wait_threads|
  ...
}

wait_threads = Open3.pipeline_start(cmd1, cmd2, ... [, opts])
...

Each cmd is a string or an array. If it is an array, the elements are passed to Process.spawn.

cmd:
  commandline                              command line string which is passed to a shell
  [env, commandline, opts]                 command line string which is passed to a shell
  [env, cmdname, arg1, ..., opts]          command name and one or more arguments (no shell)
  [env, [cmdname, argv0], arg1, ..., opts] command name and arguments including argv[0] (no shell)

Note that env and opts are optional, as for Process.spawn.

Example:

# Run xeyes in 10 seconds.
Open3.pipeline_start("xeyes") {|ts|
  sleep 10
  t = ts[0]
  Process.kill("TERM", t.pid)
  p t.value #=> #<Process::Status: pid 911 SIGTERM (signal 15)>
}

# Convert pdf to ps and send it to a printer.
# Collect error message of pdftops and lpr.
pdf_file = "paper.pdf"
printer = "printer-name"
err_r, err_w = IO.pipe
Open3.pipeline_start(["pdftops", pdf_file, "-"],
                     ["lpr", "-P#{printer}"],
                     :err=>err_w) {|ts|
  err_w.close
  p err_r.read # error messages of pdftops and lpr.
}

Open3.pipeline_w starts a list of commands as a pipeline with a pipe which connects to stdin of the first command.

Open3.pipeline_w(cmd1, cmd2, ... [, opts]) {|first_stdin, wait_threads|
  ...
}

first_stdin, wait_threads = Open3.pipeline_w(cmd1, cmd2, ... [, opts])
...
first_stdin.close

Each cmd is a string or an array. If it is an array, the elements are passed to Process.spawn.

cmd:
  commandline                              command line string which is passed to a shell
  [env, commandline, opts]                 command line string which is passed to a shell
  [env, cmdname, arg1, ..., opts]          command name and one or more arguments (no shell)
  [env, [cmdname, argv0], arg1, ..., opts] command name and arguments including argv[0] (no shell)

Note that env and opts are optional, as for Process.spawn.

Example:

Open3.pipeline_w("bzip2 -c", :out=>"/tmp/hello.bz2") {|i, ts|
  i.puts "hello"
}

Open3.popen2 is similar to Open3.popen3 except that it doesn’t create a pipe for the standard error stream.

Block form:

Open3.popen2([env,] cmd... [, opts]) {|stdin, stdout, wait_thr|
  pid = wait_thr.pid # pid of the started process.
  ...
  exit_status = wait_thr.value # Process::Status object returned.
}

Non-block form:

stdin, stdout, wait_thr = Open3.popen2([env,] cmd... [, opts])
...
stdin.close  # stdin and stdout should be closed explicitly in this form.
stdout.close

See Process.spawn for the optional hash arguments env and opts.

Example:

Open3.popen2("wc -c") {|i,o,t|
  i.print "answer to life the universe and everything"
  i.close
  p o.gets #=> "42\n"
}

Open3.popen2("bc -q") {|i,o,t|
  i.puts "obase=13"
  i.puts "6 * 9"
  p o.gets #=> "42\n"
}

Open3.popen2("dc") {|i,o,t|
  i.print "42P"
  i.close
  p o.read #=> "*"
}

Open3.popen2e is similar to Open3.popen3 except that it merges the standard output stream and the standard error stream.

Block form:

Open3.popen2e([env,] cmd... [, opts]) {|stdin, stdout_and_stderr, wait_thr|
  pid = wait_thr.pid # pid of the started process.
  ...
  exit_status = wait_thr.value # Process::Status object returned.
}

Non-block form:

stdin, stdout_and_stderr, wait_thr = Open3.popen2e([env,] cmd... [, opts])
...
stdin.close  # stdin and stdout_and_stderr should be closed explicitly in this form.
stdout_and_stderr.close

See Process.spawn for the optional hash arguments env and opts.

Example:

# check gcc warnings
source = "foo.c"
Open3.popen2e("gcc", "-Wall", source) {|i,oe,t|
  oe.each {|line|
    if /warning/ =~ line
      ...
    end
  }
}

Open stdin, stdout, and stderr streams and start external executable. In addition, a thread to wait for the started process is created. The thread has a pid method and a thread variable :pid which is the pid of the started process.

Block form:

Open3.popen3([env,] cmd... [, opts]) {|stdin, stdout, stderr, wait_thr|
  pid = wait_thr.pid # pid of the started process.
  ...
  exit_status = wait_thr.value # Process::Status object returned.
}

Non-block form:

stdin, stdout, stderr, wait_thr = Open3.popen3([env,] cmd... [, opts])
pid = wait_thr[:pid]  # pid of the started process
...
stdin.close  # stdin, stdout and stderr should be closed explicitly in this form.
stdout.close
stderr.close
exit_status = wait_thr.value  # Process::Status object returned.

The parameters env, cmd, and opts are passed to Process.spawn. A commandline string and a list of argument strings can be accepted as follows:

Open3.popen3("echo abc") {|i, o, e, t| ... }
Open3.popen3("echo", "abc") {|i, o, e, t| ... }
Open3.popen3(["echo", "argv0"], "abc") {|i, o, e, t| ... }

If the last parameter, opts, is a Hash, it is recognized as an option for Process.spawn.

Open3.popen3("pwd", :chdir=>"/") {|i,o,e,t|
  p o.read.chomp #=> "/"
}

wait_thr.value waits for the termination of the process. The block form also waits for the process when it returns.

Closing stdin, stdout and stderr does not wait for the process to complete.

You should be careful to avoid deadlocks. Since pipes are fixed length buffers, Open3.popen3(“prog”) {|i, o, e, t| o.read } deadlocks if the program generates too much output on stderr. You should read stdout and stderr simultaneously (using threads or IO.select). However, if you don’t need stderr output, you can use Open3.popen2. If merged stdout and stderr output is not a problem, you can use Open3.popen2e. If you really need stdout and stderr output as separate strings, you can consider Open3.capture3.