20191212-01

#!/bin/sh

set -e
rm -rf work
mkdir work
cd work
cat <<EOD > launcher.c; cc -Wall -Werror launcher.c -o launcher
#include <sys/types.h>
#include <sys/wait.h>
#include <stdio.h>
#include <unistd.h>
int main(int    argc,
         char **argv,
         char **arge
        )
{
  int     wait_status;

  size_t  program_index;

  pid_t   fork_result;

  char  * programs[]={"./py2-demo",
                      "./py3-demo",
                      "./sh-demo",
                      "./bash-demo",
                      "./perl-demo",
                      NULL
                     };

  argv[0]="jabberwocky";

  for(program_index=0;
      programs[program_index];
      program_index++
     )
  {
    fork_result=fork();

    if(fork_result==-1)
    {
      perror("fork()");

      return 1;
    }

    if(fork_result==0)
    {
      printf("launching %s\n",programs[program_index]);

      execve(programs[program_index],argv,arge);

      perror("execve()");

      return 1;
    }

    wait(&wait_status);
  }

  return 0;
}
EOD
cat <<EOD > py2-demo.c; cc -Wall -Werror py2-demo.c -o py2-demo
#include <sys/types.h>
#include <sys/wait.h>
#include <stdio.h>
#include <unistd.h>
int main(int    argc,
         char **argv,
         char **arge
        )
{
  int    wait_status;

  pid_t  fork_result;

  argv[0]="jabberwocky";

  fork_result=fork();

  if(fork_result==-1)
  {
    perror("fork()");

    return 1;
  }

  if(fork_result==0)
  {
    execve("./py2-demo.py",argv,arge);

    perror("execve()");

    return 1;
  }

  wait(&wait_status);
}
EOD
cat <<EOD > py2-demo.py; chmod 700 py2-demo.py
#!/usr/bin/env python2

import os
import subprocess

def get_arg0():
    return (subprocess.Popen(["ps","-p","%s" % os.getppid(),"-o","args="],
                             stdout=subprocess.PIPE).stdout.read()
                             .decode(encoding='latin1')
                             .split(" ")[0])
print get_arg0()
EOD
cat <<EOD > py3-demo.c; cc -Wall -Werror py3-demo.c -o py3-demo
#include <sys/types.h>
#include <sys/wait.h>
#include <stdio.h>
#include <unistd.h>
int main(int    argc,
         char **argv,
         char **arge
        )
{
  int    wait_status;

  pid_t  fork_result;

  argv[0]="jabberwocky";

  fork_result=fork();

  if(fork_result==-1)
  {
    perror("fork()");

    return 1;
  }

  if(fork_result==0)
  {
    execve("./py3-demo.py",argv,arge);

    perror("execve()");

    return 1;
  }

  wait(&wait_status);
}
EOD
cat <<EOD > py3-demo.py; chmod 700 py3-demo.py
#!/usr/bin/env python3

import os
import subprocess

def get_arg0():
    return subprocess.run("ps -p %s -o 'args='" % os.getppid(),
                          shell=True,
                          stdout=subprocess.PIPE,
                          stderr=subprocess.PIPE
                         ).stdout.decode(encoding='latin1').split(sep=" ")[0]

print(get_arg0())
EOD
cat <<EOD > sh-demo.c; cc -Wall -Werror sh-demo.c -o sh-demo
#include <sys/types.h>
#include <sys/wait.h>
#include <stdio.h>
#include <unistd.h>
int main(int    argc,
         char **argv,
         char **arge
        )
{
  int    wait_status;

  pid_t  fork_result;

  argv[0]="jabberwocky";

  fork_result=fork();

  if(fork_result==-1)
  {
    perror("fork()");

    return 1;
  }

  if(fork_result==0)
  {
    execve("./sh-demo.sh",argv,arge);

    perror("execve()");

    return 1;
  }

  wait(&wait_status);
}
EOD
cat <<EOD > sh-demo.sh; chmod 700 sh-demo.sh
#!/bin/sh

get_arg0()
{
  echo \$(ps -p \$PPID -o "args=" | awk '{print \$1}')
}

echo \$(get_arg0)
EOD
cat <<EOD > bash-demo.c; cc -Wall -Werror bash-demo.c -o bash-demo
#include <sys/types.h>
#include <sys/wait.h>
#include <stdio.h>
#include <unistd.h>
int main(int    argc,
         char **argv,
         char **arge
        )
{
  int    wait_status;

  pid_t  fork_result;

  argv[0]="jabberwocky";

  fork_result=fork();

  if(fork_result==-1)
  {
    perror("fork()");

    return 1;
  }

  if(fork_result==0)
  {
    execve("./bash-demo.sh",argv,arge);

    perror("execve()");

    return 1;
  }

  wait(&wait_status);
}
EOD
cat <<EOD > bash-demo.sh; chmod 700 bash-demo.sh
#!/bin/sh

get_arg0()
{
  echo \$(ps -p \$PPID -o "args=" | awk '{print \$1}')
}

echo \$(get_arg0)
EOD
cat <<EOD > perl-demo.c; cc -Wall -Werror perl-demo.c -o perl-demo
#include <sys/types.h>
#include <sys/wait.h>
#include <stdio.h>
#include <unistd.h>
int main(int    argc,
         char **argv,
         char **arge
        )
{
  int    wait_status;

  pid_t  fork_result;

  argv[0]="jabberwocky";

  fork_result=fork();

  if(fork_result==-1)
  {
    perror("fork()");

    return 1;
  }

  if(fork_result==0)
  {
    execve("./perl-demo.pl",argv,arge);

    perror("execve()");

    return 1;
  }

  wait(&wait_status);
}
EOD
cat <<EOD > perl-demo.pl; chmod 700 perl-demo.pl
#!/usr/bin/env perl

use strict;
use warnings FATAL=>"all";

sub get_arg0
{
  my \$result;
  my \$parent=getppid();
  \$result=\`ps -p \$parent -o "args=" | awk '{print \\\$1}'\`;

  chomp(\$result);
  return \$result;
}

print(get_arg0,"\n");
EOD
./launcher