How to Pass Arguments from the Parent Task to the Child Task in Rake

How do I pass an argument from a child task to a parent task in Rake

Not sure if you can set or pass a parameter, but you can use instance variables:

task :first_task  => :dep do
   puts "something else"
   puts @dir
end

task :dep do
  puts "something"
  @dir = "Foo"
end

Or just local variables:

dir = "default_dir"

task :first_task  => :dep do
   puts "something else"
   puts dir
end

task :dep do
  puts "something"
  dir = "Foo"
end

For some kinds of task, it may make more sense to set environment variables:

task :first_task  => :dep do
   puts "something else"
   puts ENV['dir']
end

task :dep do
  puts "something"
  ENV['dir'] = "Foo"
end

Rake: How do I forward params to child Rake calls?

Please check this question. If you cannot modify your tasks to add the parameters ( for some reason ), then you can use environment variables, like:

namespace :db do
  task :regenesis do
    #because of how devestating this command could be, it's going 
    # to be forced to use the Test Environment
    puts "Re-Generating the Database"
    ENV["extra_option"] = "--trace"
    Rake::Task["db:drop RAILS_ENV=test"].invoke
    Rake::Task["db:create RAILS_ENV=test"].invoke
    Rake::Task["db:create RAILS_ENV=test"].invoke
    Rake::Task["db:bootstrap RAILS_ENV=test"].invoke
  end
end

And in your tasks you'd have to look for ENV["extra_option"]

How can I pass named arguments to a Rake task?

You can say things like this:

rake some_task -- --arg=value

And then, inside your task, ARGV will be

[ 'some_task', '--arg=value' ]

so you could use OptionParser (or some other option parser) to unpack ARGV just like in any old CLI script; the funny looking -- is necessary to keep rake from trying to parse --arg=like as a rake switch.

You're probably better off with the standard environment variable approach, it isn't as ugly as all the -- stuff and it is the usual way of passing arguments to rake tasks.

parent send command line arguments to child

Code:

#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <string.h>

int main(int argc, char *argv[])
{
    pid_t   pid;
    int     status;
    int     comm[2];
    char    buffer[BUFSIZ];

    // set up pipe
    if (pipe(comm) < 0) {
        printf("pipe error\n");
        return -1;
    }
    // call fork()
    if((pid = fork()) <0)
    {
        printf("fork error %d\n", pid);
        return -1;
    }
    else if (pid == 0) {
        // -- running in child process --
        int     nChars = 0;
        close(comm[1]);
        //printf("%d \n",BUFSIZ);
        // Receive characters from parent process via pipe
        // one at a time, and count them.
        int n;
        while( (n =read(comm[0], buffer, BUFSIZ)) >0)
    {
      buffer[n] = 0;
      int oneChar, i = 0,endflag = 0;
      while((oneChar = buffer[i])!=0)
      {
       // printf("%d\n",oneChar);
        if(oneChar!=EOF)
          nChars++;
        else
        {
          endflag = 1;
          break;
        }
        i++;
      }
      //printf("%s\n",buffer);
      if(endflag)
        break;
    }
    printf("nChar : %d",nChars);
        // Return number of characters counted to parent process.
        return nChars;
    }
    else {
        // -- running in parent process --
        //int     nChars = 0;
        close(comm[0]);

        // Send characters from command line arguments starting with
        // argv[1] one at a time through pipe to child process.
        int a,c;
        char endl='\n';
        for ( a = 1; a < argc; a++) {
            for ( c = 0; c < strlen(argv[a]); c++) {
                write(comm[1], &argv[a][c], 1);
            }
        }
    printf("write end\n");
    int end = EOF;
    write(comm[1],&end,4);

        waitpid(pid, &status, 0);

        printf("child counted %d chars\n", WEXITSTATUS(status));
        return 0;
        }
}

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