Running process (filehandle-based interface)
Proc is a representation of an invocation of an external process. It provides access to the input, output and error stream as well as the exit code. It is typically created through the
my = run 'echo', 'Hallo world', :out;my = .out.slurp: :close;say "Output was $captured-output.perl()"; # OUTPUT: «Output was "Hallo world\n"␤»
Piping several commands is easy too. To achieve the equivalent of the pipe
echo "Hello, world" | cat -n in Perl 6, and capture the output from the second command, you can do
my = run 'echo', 'Hello, world', :out;my = run 'cat', '-n', :in(.out), :out;say .out.get;
You can also feed the
:in pipe directly from your program, by setting it to
True, which will make the pipe available via
.in method on the
my = run "cat", "-n", :in, :out;.in.say: "Hello,\nworld!";.in.close;say .out.slurp: :close;# OUTPUT: «1 Hello,␤# 2 world!␤»
In order to capture the standard error
:err can be supplied:
my = run "ls", "-l", ".", "qqrq", :out, :err;my = .out.slurp: :close;my = .err.slurp: :close;my = .exitcode;
Use Proc::Async for non-blocking operations.
method new(Proc:: = '-',: = '-',: = '-',Bool : = False,Bool : = True,Bool : = False,Str : = 'UTF-8',Str : = "\n",--> Proc)sub shell(,: = '-',: = '-',: = '-',Bool : = False,Bool : = True,Bool : = False,Str : = 'UTF-8',Str : = "\n",: = ,Hash() : =--> Proc)
new creates a new
Proc object, whereas
shell create one and spawn it with the command and arguments provided in
$err are the three standard streams of the to-be-launched program, and default to
"-" meaning they inherit the stream from the parent process. Setting one (or more) of them to
True makes the stream available as an IO::Pipe object of the same name, like for example
$proc.out. You can set them to
False to discard them. Or you can pass an existing IO::Handle object (for example
IO::Pipe) in, in which case this handle is used for the stream.
Please bear in mind that the process streams reside in process variables, not in the dynamic variables that make them available to our programs. Thus, modifying the dynamic filehandle variables (such as
$*OUT) inside the host process will have no effect in the spawned process, unlike
$*ENV, whose changes will be actually reflected in it.
my = "/tmp/program.p6";my =spurt , ;.put: "1. standard output before doing anything weird";.put: "3. everything should be back to normal";# OUTPUT# 1. standard output before doing anything weird# /tmp/program.p6: This goes to standard output# 3. everything should be back to normal# /tmp/out.txt will contain:# 2. temp redefine standard output before this message
This program shows that the program spawned with
shell is not using the temporary
$*OUT value defined in the host process (redirected to
/tmp/out.txt), but the initial
STDOUT defined in the process.
$bin controls whether the streams are handled as binary (i.e. Blob object) or text (i.e. Str objects). If
$bin is False,
$enc holds the character encoding to encode strings sent to the input stream and decode binary data from the output and error streams.
$chomp set to
True, newlines are stripped from the output and err streams when reading with
$nl controls what your idea of a newline is.
$merge is set to True, the standard output and error stream end up merged in
sub run(* ($, *@),: = '-',: = '-',: = '-',Bool : = False,Bool : = True,Bool : = False,Str : = 'UTF-8',Str : = "\n",: = ,Hash() : =--> Proc)
Runs an external command without involving a shell and returns a Proc object. By default, the external command will print to standard output and error, and read from standard input.
run 'touch', '>foo.txt'; # Create a file named >foo.txtrun <<rm >foo.txt>>; # Another way to use run, using word quoting for the# arguments
If you want to pass some variables you can still use
< >, but try to avoid using
« » as it will do word splitting if you forget to quote variables:
my = ‘--my arbitrary filename’;run ‘touch’, ‘--’, ; # RIGHTrun <touch -->, ; # RIGHTrun «touch -- "$file"»; # RIGHT but WRONG if you forget quotesrun «touch -- »; # WRONG; touches ‘--my’, ‘arbitrary’ and ‘filename’run ‘touch’, ; # WRONG; error from `touch`run «touch "$file"»; # WRONG; error from `touch`
-- is required for many programs to disambiguate between command-line arguments and filenames that begin with hyphens.
run 'false'; # SUNK! Will throwrun('false').so; # OK. Evaluates Proc in Bool context; no sinking
If you want to capture standard output or error instead of having it printed directly you can use the
:err arguments respectively, which will make them available using the
my = run 'echo', 'Perl 6 is Great!', :out, :err;.out.slurp(:close).say; # OUTPUT: «Perl 6 is Great!␤».err.slurp(:close).say; # OUTPUT: «␤»
You can use these arguments to redirect them to a filehandle, thus creating a kind of pipe:
my = open :w, '/tmp/cur-dir-ls-alt.txt';my = run "ls", "-alt", :out();# (The file will contain the output of the ls -alt command)
new for more examples.
method sink(--> Nil)
When sunk, the
Proc object will throw X::Proc::Unsuccessful if the process it ran exited unsuccessfully.
method spawn(* ($, *@), : = , Hash() : = --> Bool)
Proc object with the given command, argument list, working directory, and environment.
method shell(, : = , : --> Bool)
Proc object with the given command and environment which are passed through to the shell for parsing and execution. See
IO::shell for an explanation of which shells are used by default in the most common operating systems.
method command(Proc: --> List)
The command method is an accessor to a list containing the arguments that were passed when the Proc object was executed via
$*PID value of the process if available, or
method exitcode(Proc: --> Int)
Returns the exit code of the external process, or -1 if it has not exited yet.
Returns the signal number with which the external process was killed, or
0 or an undefined value otherwise.