Programs running other programs and communicating with them
Many programs need to be able to run other programs. Running a program in Perl 6 is as easy as:
run 'git', 'status';
This line runs the program named "git" and passes "git" and "status" to its command-line. It will find the program using the
If you would like to run a program by sending a command-line to the shell, there's a tool for that as well. All shell meta characters are interpreted by the shell, including pipes, redirects, environment variable substitutions and so on.
shell 'ls -lR | gzip -9 > ls-lR.gz';
Caution should be taken when using
shell with user input.
shell return a Proc object, which can be used to communicate with the process in more detail. Please note that unless you close all output pipes, the program will usually not terminate.
my = run 'git', 'log', '--oneline', :out;for .out.lines ->.out.close();
If the program fails (exits with a non-zero exit code), it will throw an exception when the returned Proc object is sunk. You can save it into a variable, even anonymous one, to prevent the sinking:
$ = run '/bin/false'; # does not sink the Proc and so does not throw
You can tell the
Proc object to capture output as a filehandle by passing the
:err flags. You may also pass input via the
my = run 'echo', 'Hello, world', :out;my = run 'cat', '-n', :in(.out), :out;say .out.get;.out.close();
You may also use
Proc to capture the PID, send signals to the application, and check the exitcode.
my = run 'crontab', '-l';if .exitcode == 0else
When you need more control over the communication with and from another process, you will want to make use of Proc::Async. This class provides support for asynchronous communication with a program, as well as the ability to send signals to that program.
# Get ready to run the programmy = Proc::Async.new('tail', '-f', '/var/log/system.log');.stdout.tap(-> );.stderr.tap(-> );# Start the programmy = .start;sleep 10;# Tell the program to stop.kill('QUIT');# Wait for the program to finishawait ;
Here is a small program that uses the "tail" program to print out the contents of the log named
system.log for 10 seconds and then tells the program to stop with a QUIT signal.
Proc provides access to output using
Proc::Async provides access using asynchronous supplies (see Supply).
If you want to run a program and do some work while you wait for the original program to finish, the
start routine returns a Promise, which is kept when the program quits.
write method to pass data into the program.