IO.popen([env,] cmd, mode="r" [, opt]) {|io| block } â obj
Runs the specified command as a subprocess; the subprocess's standard
input and output will be connected to the returned IO
object.
The PID of the started process can be obtained by #pid method.
cmd is a string or an array as follows.
cmd: "-" : fork commandline : command line string which is passed to a shell [env, cmdname, arg1, ..., opts] : command name and zero or more arguments (no shell) [env, [cmdname, argv0], arg1, ..., opts] : command name, argv[0] and zero or more arguments (no shell) (env and opts are optional.)
If cmd is a String
â-
'', then a
new instance of Ruby is started as the subprocess.
If cmd is an Array
of String
, then it
will be used as the subprocess's argv
bypassing a shell.
The array can contains a hash at first for environments and a hash at last
for options similar to spawn
.
The default mode for the new file object is âr'', but mode may be set to any of the modes listed in the description for class IO. The last argument opt qualifies mode.
# set IO encoding IO.popen("nkf -e filename", :external_encoding=>"EUC-JP") {|nkf_io| euc_jp_string = nkf_io.read } # merge standard output and standard error using # spawn option. See the document of Kernel.spawn. IO.popen(["ls", "/", :err=>[:child, :out]]) {|ls_io| ls_result_with_error = ls_io.read } # spawn options can be mixed with IO options IO.popen(["ls", "/"], :err=>[:child, :out]) {|ls_io| ls_result_with_error = ls_io.read }
Raises exceptions which IO.pipe
and Kernel.spawn
raise.
If a block is given, Ruby will run the command as a child connected to Ruby
with a pipe. Ruby's end of the pipe will be passed as a parameter to
the block. At the end of block, Ruby close the pipe and sets
$?
. In this case IO.popen
returns the value of
the block.
If a block is given with a cmd of â-
'', the
block will be run in two separate processes: once in the parent, and once
in a child. The parent process will be passed the pipe object as a
parameter to the block, the child version of the block will be passed
nil
, and the child's standard in and standard out will be
connected to the parent through the pipe. Not available on all platforms.
f = IO.popen("uname") p f.readlines f.close puts "Parent is #{Process.pid}" IO.popen("date") { |f| puts f.gets } IO.popen("-") {|f| $stderr.puts "#{Process.pid} is here, f is #{f.inspect}"} p $? IO.popen(%w"sed -e s|^|<foo>| -e s&$&;zot;&", "r+") {|f| f.puts "bar"; f.close_write; puts f.gets }
produces:
["Linux\n"] Parent is 21346 Thu Jan 15 22:41:19 JST 2009 21346 is here, f is #<IO:fd 3> 21352 is here, f is nil #<Process::Status: pid 21352 exit 0> <foo>bar;zot;
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