fish-shell/exec.cpp

/** \file exec.c
	Functions for executing a program.

	Some of the code in this file is based on code from the Glibc
	manual, though I the changes performed have been massive.
*/

#include "config.h"

#include <stdlib.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <termios.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#include <wchar.h>
#include <string.h>
#include <limits.h>
#include <signal.h>
#include <sys/wait.h>
#include <assert.h>
#include <dirent.h>
#include <time.h>
#include <vector>
#include <deque>
#include <algorithm>
#include <memory>

#ifdef HAVE_SIGINFO_H
#include <siginfo.h>
#endif

#include "fallback.h"
#include "util.h"

#include "common.h"
#include "wutil.h"
#include "proc.h"
#include "exec.h"
#include "parser.h"
#include "builtin.h"
#include "function.h"
#include "env.h"
#include "wildcard.h"
#include "sanity.h"
#include "expand.h"
#include "signal.h"

#include "parse_util.h"

/**
   file descriptor redirection error message
*/
#define FD_ERROR   _( L"An error occurred while redirecting file descriptor %d" )

/**
   file descriptor redirection error message
*/
#define WRITE_ERROR   _( L"An error occurred while writing output" )

/**
   file redirection error message
*/
#define FILE_ERROR _( L"An error occurred while redirecting file '%ls'" )

/**
   file redirection clobbering error message
*/
#define NOCLOB_ERROR _( L"The file '%ls' already exists" )

/**
   fork error message
*/
#define FORK_ERROR _( L"Could not create child process - exiting" )

/**
   The number of times to try to call fork() before giving up
*/
#define FORK_LAPS 5

/**
   The number of nanoseconds to sleep between attempts to call fork()
*/
#define FORK_SLEEP_TIME 1000000

/**
   Base open mode to pass to calls to open
*/
#define OPEN_MASK 0666

/**
   List of all pipes used by internal pipes. These must be closed in
   many situations in order to make sure that stray fds aren't lying
   around.
*/
static std::vector<int> open_fds;

static int set_child_group( job_t *j, process_t *p, int print_errors );

static void exec_write_and_exit( int fd, char *buff, size_t count, int status )
{
	if( write_loop(fd, buff, count) == -1 ) 
	{
		debug( 0, WRITE_ERROR);
		wperror( L"write" );
		exit(status);
	}
	exit( status );
}


void exec_close( int fd )
{
	if( fd < 0 )
	{
		debug( 0, L"Called close on invalid file descriptor " );
		return;
	}
	
	while( close(fd) == -1 )
	{
		if( errno != EINTR )
		{
			debug( 1, FD_ERROR, fd );
			wperror( L"close" );
			break;
		}
	}
	
    /* Maybe remove this form our set of open fds */
    open_fds.erase(std::remove(open_fds.begin(), open_fds.end(), fd), open_fds.end());
}

int exec_pipe( int fd[2])
{
	int res;
	
	while( ( res=pipe( fd ) ) )
	{
		if( errno != EINTR )
		{
			wperror(L"pipe");
			return res;
		}
	}	
	
	debug( 4, L"Created pipe using fds %d and %d", fd[0], fd[1]);
	
    open_fds.push_back(fd[0]);
    open_fds.push_back(fd[1]);
	
	return res;
}

/**
   Check if the specified fd is used as a part of a pipeline in the
   specidied set of IO redirections.

   \param fd the fd to search for
   \param io the set of io redirections to search in
*/
static int use_fd_in_pipe( int fd, io_data_t *io )
{	
	if( !io )
		return 0;
	
	if( ( io->io_mode == IO_BUFFER ) || 
		( io->io_mode == IO_PIPE ) )
	{
		if( io->param1.pipe_fd[0] == fd ||
			io->param1.pipe_fd[1] == fd )
			return 1;
	}
		
	return use_fd_in_pipe( fd, io->next );
}


/**
   Close all fds in open_fds, except for those that are mentioned in
   the redirection list io. This should make sure that there are no
   stray opened file descriptors in the child.
   
   \param io the list of io redirections for this job. Pipes mentioned
   here should not be closed.
*/
static void close_unused_internal_pipes( io_data_t *io )
{
    /* A call to exec_close will modify open_fds, so be careful how we walk */
    for (size_t i=0; i < open_fds.size(); i++) {
        int fd = open_fds.at(i);
        if( !use_fd_in_pipe( fd, io) )
        {
            debug( 4, L"Close fd %d, used in other context", fd );
            exec_close( fd );
            i--;
        }
    }
}

/**
   Make sure the fd used by this redirection is not used by i.e. a pipe. 
*/
void free_fd( io_data_t *io, int fd )
{
	if( !io )
		return;
	
	if( ( io->io_mode == IO_PIPE ) || ( io->io_mode == IO_BUFFER ) )
	{
		int i;
		for( i=0; i<2; i++ )
		{
			if(io->param1.pipe_fd[i] == fd )
			{
				while(1)
				{
					if( (io->param1.pipe_fd[i] = dup(fd)) == -1)
					{
						 if( errno != EINTR )
						{
							debug( 1, 
								   FD_ERROR,
								   fd );							
							wperror( L"dup" );
							FATAL_EXIT();
						}
					}
					else
					{
						break;
					}
				}
			}
		}
	}
	free_fd( io->next, fd );
}

/**
   Set up a childs io redirections. Should only be called by
   setup_child_process(). Does the following: First it closes any open
   file descriptors not related to the child by calling
   close_unused_internal_pipes() and closing the universal variable
   server file descriptor. It then goes on to perform all the
   redirections described by \c io.

   \param io the list of IO redirections for the child

   \return 0 on sucess, -1 on failiure
*/
static int handle_child_io( io_data_t *io )
{

	close_unused_internal_pipes( io );

	for( ; io; io=io->next )
	{
		int tmp;

		if( io->io_mode == IO_FD && io->fd == io->param1.old_fd )
		{
			continue;
		}

		if( io->fd > 2 )
		{
			/*
			  Make sure the fd used by this redirection is not used by e.g. a pipe. 
			*/
			free_fd( io, io->fd );
		}
				
		switch( io->io_mode )
		{
			case IO_CLOSE:
			{
				if( close(io->fd) )
				{
					debug( 0, _(L"Failed to close file descriptor %d"), io->fd );
					wperror( L"close" );
				}
				break;
			}

			case IO_FILE:
			{
				if( (tmp=wopen( io->filename,
						io->param2.flags, OPEN_MASK ) )==-1 )
				{
					if( ( io->param2.flags & O_EXCL ) &&
					    ( errno ==EEXIST ) )
					{
						debug( 1, 
						       NOCLOB_ERROR,
						       io->filename.c_str() );
					}
					else
					{
						debug( 1, 
						       FILE_ERROR,
						       io->filename.c_str() );
										
						wperror( L"open" );
					}
					
					return -1;
				}
				else if( tmp != io->fd)
				{
					/*
					  This call will sometimes fail, but that is ok,
					  this is just a precausion.
					*/
					close(io->fd);
							
					if(dup2( tmp, io->fd ) == -1 )
					{
						debug( 1, 
							   FD_ERROR,
							   io->fd );
						wperror( L"dup2" );
						return -1;
					}
					exec_close( tmp );
				}				
				break;
			}
			
			case IO_FD:
			{
				/*
				  This call will sometimes fail, but that is ok,
				  this is just a precausion.
				*/
				close(io->fd);

				if( dup2( io->param1.old_fd, io->fd ) == -1 )
				{
					debug( 1, 
						   FD_ERROR,
						   io->fd );
					wperror( L"dup2" );
					return -1;
				}
				break;
			}
			
			case IO_BUFFER:
			case IO_PIPE:
			{
				int write_pipe;
				
				write_pipe = !io->is_input;
/*
				debug( 0,
					   L"%ls %ls on fd %d (%d %d)", 
					   write_pipe?L"write":L"read", 
					   (io->io_mode == IO_BUFFER)?L"buffer":L"pipe",
					   io->fd,
					   io->param1.pipe_fd[0],
					   io->param1.pipe_fd[1]);
*/
				if( dup2( io->param1.pipe_fd[write_pipe], io->fd ) != io->fd )
				{
					debug( 1, PIPE_ERROR );
					wperror( L"dup2" );
					return -1;
				}

				if( write_pipe ) 
				{
					exec_close( io->param1.pipe_fd[0]);
					exec_close( io->param1.pipe_fd[1]);
				}
				else
				{
					exec_close( io->param1.pipe_fd[0] );
				}
				break;
			}
			
		}
	}

	return 0;
	
}

/**
   Initialize a new child process. This should be called right away
   after forking in the child process. If job control is enabled for
   this job, the process is put in the process group of the job, all
   signal handlers are reset, signals are unblocked (this function may
   only be called inside the exec function, which blocks all signals),
   and all IO redirections and other file descriptor actions are
   performed.

   \param j the job to set up the IO for
   \param p the child process to set up

   \return 0 on sucess, -1 on failiure. When this function returns,
   signals are always unblocked. On failiure, signal handlers, io
   redirections and process group of the process is undefined.
*/
static int setup_child_process( job_t *j, process_t *p )
{
	int res=0;
	
	if( p )
	{
		res = set_child_group( j, p, 1 );
	}
	
	if( !res )	
	{
		res = handle_child_io( j->io );
		if( p != 0 && res )
		{
			exit( 1 );
		}
	}
	
	/* Set the handling for job control signals back to the default.  */
	if( !res )
	{
		signal_reset_handlers();
	}
	
	/* Remove all signal blocks */
	signal_unblock();	
	
	return res;
	
}

/**
   Returns the interpreter for the specified script. Returns false if file
   is not a script with a shebang.
 */
static bool get_interpreter( const wcstring &file, wcstring &interpreter )
{
    wcstring res;
	FILE *fp = wfopen( file, "r" );
	if( fp )
	{
		while( 1 )
		{
			wint_t ch = getwc( fp );
			if( ch == WEOF )
				break;
			if( ch == L'\n' )
				break;
            res.push_back(ch);
		}
        fclose(fp);
	}
	
	if (string_prefixes_string(L"#! /", res)) {
        interpreter = 3 + res.c_str();
        return true;
    } else if (string_prefixes_string(L"#!/", res)) {
        interpreter = 2 + res.c_str();
        return true;
    } else {
        return false;
    }
}

								 
/**
   This function is executed by the child process created by a call to
   fork(). It should be called after \c setup_child_process. It calls
   execve to replace the fish process image with the command specified
   in \c p. It never returns.
*/
static void launch_process( process_t *p )
{
    FILE* f;
	int err;
	
//	debug( 1, L"exec '%ls'", p->argv[0] );

	char **argv = wcsv2strv(p->get_argv());
	char **envv = env_export_arr( 0 );
	
	execve ( wcs2str(p->actual_cmd), 
		 argv,
		 envv );
	
	err = errno;
	
	/* 
	   Something went wrong with execve, check for a ":", and run
	   /bin/sh if encountered. This is a weird predecessor to the shebang
	   that is still sometimes used since it is supported on Windows.
	*/
	f = wfopen(p->actual_cmd, "r");
	if( f )
	{
		char begin[1] = {0};
		size_t read;
		
		read = fread(begin, 1, 1, f);
		fclose( f );
		
		if( (read==1) && (begin[0] == ':') )
		{
            
            wcstring_list_t argv;

			const wchar_t *sh_command = L"/bin/sh";
            argv.push_back(sh_command);
            argv.push_back(p->actual_cmd);
			for(size_t i=1; p->argv(i) != NULL; i++ ){
				argv.push_back(p->argv(i));
			}
			
			p->set_argv(argv);
			p->actual_cmd = wcsdup(sh_command);

			char **res_real = wcsv2strv( p->get_argv() );
			
			execve ( wcs2str(p->actual_cmd), 
				 res_real,
				 envv );
		}
	}
	
	errno = err;
	debug( 0, 
	       _( L"Failed to execute process '%ls'. Reason:" ),
	       p->actual_cmd );
	
	switch( errno )
	{
		
		case E2BIG:
		{
			size_t sz = 0;
			char **p;

			wcstring sz1, sz2;
			
			long arg_max = -1;

			for(p=argv; *p; p++)
			{
				sz += strlen(*p)+1;
			}
			
			for(p=envv; *p; p++)
			{
				sz += strlen(*p)+1;
			}
			
            sz1 = format_size(sz);

			arg_max = sysconf( _SC_ARG_MAX );
			
			if( arg_max > 0 )
			{
				sz2 = format_size(arg_max);
				
				debug( 0,
				       L"The total size of the argument and environment lists (%ls) exceeds the operating system limit of %ls.",
				       sz1.c_str(),
				       sz2.c_str());
			}
			else
			{
				debug( 0,
				       L"The total size of the argument and environment lists (%ls) exceeds the operating system limit.",
				       sz1.c_str());
			}
			
			debug( 0, 
			       L"Try running the command again with fewer arguments.");			
			exit(STATUS_EXEC_FAIL);
			
			break;
		}

		case ENOEXEC:
		{
			wperror(L"exec");
			
			debug(0, L"The file '%ls' is marked as an executable but could not be run by the operating system.", p->actual_cmd);
			exit(STATUS_EXEC_FAIL);
		}

		case ENOENT:
		{
            wcstring interpreter;
			if( get_interpreter(p->actual_cmd, interpreter) && waccess( interpreter, X_OK ) )
			{
				debug(0, L"The file '%ls' specified the interpreter '%ls', which is not an executable command.", p->actual_cmd, interpreter.c_str() );
			}
			else
			{
				debug(0, L"The file '%ls' or a script or ELF interpreter does not exist, or a shared library needed for file or interpreter cannot be found.", p->actual_cmd);
			}
			
			exit(STATUS_EXEC_FAIL);
		}

		case ENOMEM:
		{
			debug(0, L"Out of memory");
			exit(STATUS_EXEC_FAIL);
		}

		default:
		{
			wperror(L"exec");
			
			//		debug(0, L"The file '%ls' is marked as an executable but could not be run by the operating system.", p->actual_cmd);
			exit(STATUS_EXEC_FAIL);
		}
	}
	
}


/**
   Check if the IO redirection chains contains redirections for the
   specified file descriptor
*/
static int has_fd( io_data_t *d, int fd )
{
	return io_get( d, fd ) != 0;
}


/**
   Free a transmogrified io chain. Only the chain itself and resources
   used by a transmogrified IO_FILE redirection are freed, since the
   original chain may still be needed.
*/
static void io_untransmogrify( io_data_t * in, io_data_t *out )
{
	if( !out )
		return;
	io_untransmogrify( in->next, out->next );
	switch( in->io_mode )
	{
		case IO_FILE:
			exec_close( out->param1.old_fd );
			break;
	}	
	delete out;
}


/**
   Make a copy of the specified io redirection chain, but change file
   redirection into fd redirection. This makes the redirection chain
   suitable for use as block-level io, since the file won't be
   repeatedly reopened for every command in the block, which would
   reset the cursor position.

   \return the transmogrified chain on sucess, or 0 on failiure
*/
static io_data_t *io_transmogrify( io_data_t * in )
{
	if( !in )
		return 0;
	
	std::auto_ptr<io_data_t> out(new io_data_t());
	
	out->fd = in->fd;
	out->io_mode = IO_FD;
	out->param2.close_old = 1;
	out->next=0;
		
	switch( in->io_mode )
	{
		/*
		  These redirections don't need transmogrification. They can be passed through.
		*/
		case IO_FD:
		case IO_CLOSE:
		case IO_BUFFER:
		case IO_PIPE:
		{
            *out = *in;
			break;
		}

		/*
		  Transmogrify file redirections
		*/
		case IO_FILE:
		{
			int fd;
			
			if( (fd=wopen( in->filename, in->param2.flags, OPEN_MASK ) )==-1 )
			{
				debug( 1, 
					   FILE_ERROR,
					   in->filename.c_str() );
								
				wperror( L"open" );
				return NULL;
			}	

			out->param1.old_fd = fd;
			break;
		}
	}
	
	if( in->next)
	{
		out->next = io_transmogrify( in->next );
		if( !out->next )
		{
			io_untransmogrify( in, out.release() );
			return NULL;
		}
	}
	
	return out.release();
}

/**
   Morph an io redirection chain into redirections suitable for
   passing to eval, call eval, and clean up morphed redirections.

   \param def the code to evaluate
   \param block_type the type of block to push on evaluation
   \param io the io redirections to be performed on this block
*/

static void internal_exec_helper( parser_t &parser,
                                  const wchar_t *def, 
								  enum block_type_t block_type,
								  io_data_t *io )
{
	io_data_t *io_internal = io_transmogrify( io );
	int is_block_old=is_block;
	is_block=1;
	
	/*
	  Did the transmogrification fail - if so, set error status and return
	*/
	if( io && !io_internal )
	{
		proc_set_last_status( STATUS_EXEC_FAIL );
		return;
	}
	
	signal_unblock();
	
	parser.eval( def, io_internal, block_type );		
	
	signal_block();
	
	io_untransmogrify( io, io_internal );
	job_reap( 0 );
	is_block=is_block_old;
}

/**
   This function should be called by both the parent process and the
   child right after fork() has been called. If job control is
   enabled, the child is put in the jobs group, and if the child is
   also in the foreground, it is also given control of the
   terminal. When called in the parent process, this function may
   fail, since the child might have already finished and called
   exit. The parent process may safely ignore the exit status of this
   call.

   Returns 0 on sucess, -1 on failiure. 
*/
static int set_child_group( job_t *j, process_t *p, int print_errors )
{
	int res = 0;
	
	if( job_get_flag( j, JOB_CONTROL ) )
	{
		if (!j->pgid)
		{
			j->pgid = p->pid;
		}
		
		if( setpgid (p->pid, j->pgid) )
		{
			if( getpgid( p->pid) != j->pgid && print_errors )
			{
				debug( 1, 
				       _( L"Could not send process %d, '%ls' in job %d, '%ls' from group %d to group %d" ),
				       p->pid,
				       p->argv0(),
				       j->job_id,
				       j->command_cstr(),
				       getpgid( p->pid),
				       j->pgid );

				wperror( L"setpgid" );
				res = -1;
			}
		}
	}
	else
	{
		j->pgid = getpid();
	}

	if( job_get_flag( j, JOB_TERMINAL ) && job_get_flag( j, JOB_FOREGROUND ) )
	{
		if( tcsetpgrp (0, j->pgid) && print_errors )
		{
			debug( 1, _( L"Could not send job %d ('%ls') to foreground" ), 
				   j->job_id, 
				   j->command_cstr() );
			wperror( L"tcsetpgrp" );
			res = -1;
		}
	}

	return res;
}

/**
   This function is a wrapper around fork. If the fork calls fails
   with EAGAIN, it is retried FORK_LAPS times, with a very slight
   delay between each lap. If fork fails even then, the process will
   exit with an error message.
*/
static pid_t exec_fork()
{
	pid_t pid;
	struct timespec pollint;
	int i;
	
	for( i=0; i<FORK_LAPS; i++ )
	{
		pid = fork();
		if( pid >= 0)
		{
			return pid;
		}
		
		if( errno != EAGAIN )
		{
			break;
		}

		pollint.tv_sec = 0;
		pollint.tv_nsec = FORK_SLEEP_TIME;

		/*
		  Don't sleep on the final lap - sleeping might change the
		  value of errno, which will break the error reporting below.
		*/
		if( i != FORK_LAPS-1 )
		{
			nanosleep( &pollint, NULL );
		}
	}
	
	debug( 0, FORK_ERROR );
	wperror (L"fork");
	FATAL_EXIT();
}


/**
   Perform output from builtins
 */
static void do_builtin_io( const wchar_t *out, const wchar_t *err )
{

	if( out )
	{
		if( fwprintf( stdout, L"%ls", out ) == -1 || fflush( stdout ) == EOF )
		{
			debug( 0, L"Error while writing to stdout" );
			wperror( L"fwprintf" );
			show_stackframe();
		}
	}
	
	if( err )
	{
		if( fwprintf( stderr, L"%ls", err ) == -1 || fflush( stderr ) == EOF )
		{
			/*
			  Can't really show any error message here, since stderr is
			  dead.
			*/
		}
	}
	
} 


void exec( parser_t &parser, job_t *j )
{
	process_t *p;
	pid_t pid;
	int mypipe[2];
	sigset_t chldset; 
	int skip_fork;
	
	io_data_t pipe_read, pipe_write;
	io_data_t *tmp;

	io_data_t *io_buffer =0;

	/*
	  Set to 1 if something goes wrong while exec:ing the job, in
	  which case the cleanup code will kick in.
	*/
	int exec_error=0;

	int needs_keepalive = 0;
	process_t keepalive;
	

	CHECK( j, );
	CHECK_BLOCK();
	
	if( no_exec )
		return;
	
	sigemptyset( &chldset );
	sigaddset( &chldset, SIGCHLD );
	
	debug( 4, L"Exec job '%ls' with id %d", j->command_cstr(), j->job_id );	
	
	if( parser.block_io )
	{
		if( j->io )
		{
			j->io = io_add( io_duplicate(parser.block_io), j->io );
		}
		else
		{
			j->io=io_duplicate(parser.block_io);				
		}
	}

	
	io_data_t *input_redirect;

	for( input_redirect = j->io; input_redirect; input_redirect = input_redirect->next )
	{
		if( (input_redirect->io_mode == IO_BUFFER) && 
			input_redirect->is_input )
		{
			/*
			  Input redirection - create a new gobetween process to take
			  care of buffering
			*/
			process_t *fake = new process_t();
            fake->type  = INTERNAL_BUFFER;
			fake->pipe_write_fd = 1;
			j->first_process->pipe_read_fd = input_redirect->fd;
			fake->next = j->first_process;
			j->first_process = fake;
			break;
		}
	}
	
	if( j->first_process->type==INTERNAL_EXEC )
	{
		/*
		  Do a regular launch -  but without forking first...
		*/
		signal_block();

		/*
		  setup_child_process makes sure signals are properly set
		  up. It will also call signal_unblock
		*/
		if( !setup_child_process( j, 0 ) )
		{
			/*
			  launch_process _never_ returns
			*/
			launch_process( j->first_process );
		}
		else
		{
			job_set_flag( j, JOB_CONSTRUCTED, 1 );
			j->first_process->completed=1;
			return;
		}

	}	

	pipe_read.fd=0;
	pipe_write.fd=1;
	pipe_read.io_mode=IO_PIPE;
	pipe_read.param1.pipe_fd[0] = -1;
	pipe_read.param1.pipe_fd[1] = -1;
	pipe_read.is_input = 1;

	pipe_write.io_mode=IO_PIPE;
	pipe_write.is_input = 0;
	pipe_read.next=0;
	pipe_write.next=0;
	pipe_write.param1.pipe_fd[0]=pipe_write.param1.pipe_fd[1]=-1;
	
	j->io = io_add( j->io, &pipe_write );
	
	signal_block();

	/*
	  See if we need to create a group keepalive process. This is
	  a process that we create to make sure that the process group
	  doesn't die accidentally, and is often needed when a
	  builtin/block/function is inside a pipeline, since that
	  usually means we have to wait for one program to exit before
	  continuing in the pipeline, causing the group leader to
	  exit.
	*/
	
	if( job_get_flag( j, JOB_CONTROL ) )
	{
		for( p=j->first_process; p; p = p->next )
		{
			if( p->type != EXTERNAL )
			{
				if( p->next )
				{
					needs_keepalive = 1;
					break;
				}
				if( p != j->first_process )
				{
					needs_keepalive = 1;
					break;
				}
				
			}
			
		}
	}
		
	if( needs_keepalive )
	{
		keepalive.pid = exec_fork();

		if( keepalive.pid == 0 )
		{
			keepalive.pid = getpid();
			set_child_group( j, &keepalive, 1 );
			pause();			
			exit(0);
		}
		else
		{
			set_child_group( j, &keepalive, 0 );			
		}
	}
	
	/*
	  This loop loops over every process_t in the job, starting it as
	  appropriate. This turns out to be rather complex, since a
	  process_t can be one of many rather different things.

	  The loop also has to handle pipelining between the jobs.
	*/

	for( p=j->first_process; p; p = p->next )
	{
		mypipe[1]=-1;
		skip_fork=0;
		
		pipe_write.fd = p->pipe_write_fd;
		pipe_read.fd = p->pipe_read_fd;
//		debug( 0, L"Pipe created from fd %d to fd %d", pipe_write.fd, pipe_read.fd );
		

		/* 
		   This call is used so the global environment variable array
		   is regenerated, if needed, before the fork. That way, we
		   avoid a lot of duplicate work where EVERY child would need
		   to generate it, since that result would not get written
		   back to the parent. This call could be safely removed, but
		   it would result in slightly lower performance - at least on
		   uniprocessor systems.
		*/
		if( p->type == EXTERNAL )
			env_export_arr( 1 );
		
		
		/*
		  Set up fd:s that will be used in the pipe 
		*/
		
		if( p == j->first_process->next )
		{
			j->io = io_add( j->io, &pipe_read );
		}
		
		if( p->next )
		{
//			debug( 1, L"%ls|%ls" , p->argv[0], p->next->argv[0]);
			
			if( exec_pipe( mypipe ) == -1 )
			{
				debug( 1, PIPE_ERROR );
				wperror (L"pipe");
				exec_error=1;
				break;
			}

			memcpy( pipe_write.param1.pipe_fd, mypipe, sizeof(int)*2);
		}
		else
		{
			/*
			  This is the last element of the pipeline.
			  Remove the io redirection for pipe output.
			*/
			j->io = io_remove( j->io, &pipe_write );
			
		}

		switch( p->type )
		{
			case INTERNAL_FUNCTION:
			{
				wchar_t * def=0;
				int shadows;
				

				/*
				  Calls to function_get_definition might need to
				  source a file as a part of autoloading, hence there
				  must be no blocks.
				*/

				signal_unblock();
				const wchar_t * orig_def = function_get_definition( p->argv0() );
                
                // function_get_named_arguments may trigger autoload, which deallocates the orig_def.
                // We should make function_get_definition return a wcstring (but how to handle NULL...)
                if (orig_def)
                    def = wcsdup(orig_def);
                
				wcstring_list_t named_arguments = function_get_named_arguments( p->argv0() );
				shadows = function_get_shadows( p->argv0() );

				signal_block();
				
				if( def == NULL )
				{
					debug( 0, _( L"Unknown function '%ls'" ), p->argv0() );
					break;
				}
				parser.push_block( shadows?FUNCTION_CALL:FUNCTION_CALL_NO_SHADOW );
				
				parser.current_block->state2<process_t *>() = p;
				parser.current_block->state1<wcstring>() = p->argv0();
						

				/*
				  set_argv might trigger an event
				  handler, hence we need to unblock
				  signals.
				*/
				signal_unblock();
				parse_util_set_argv( p->get_argv()+1, named_arguments );
				signal_block();
								
				parser.forbid_function( p->argv0() );

				if( p->next )
				{
					io_buffer = io_buffer_create( 0 );					
					j->io = io_add( j->io, io_buffer );
				}
				
				internal_exec_helper( parser, def, TOP, j->io );
				
				parser.allow_function();
				parser.pop_block();
                free(def);
				
				break;				
			}
			
			case INTERNAL_BLOCK:
			{
				if( p->next )
				{
					io_buffer = io_buffer_create( 0 );					
					j->io = io_add( j->io, io_buffer );
				}
                
				internal_exec_helper( parser, p->argv0(), TOP, j->io );			
				break;
				
			}

			case INTERNAL_BUILTIN:
			{
				int builtin_stdin=0;
				int fg;
				int close_stdin=0;

				/*
				  If this is the first process, check the io
				  redirections and see where we should be reading
				  from.
				*/
				if( p == j->first_process )
				{
					io_data_t *in = io_get( j->io, 0 );
					
					if( in )
					{
						switch( in->io_mode )
						{
							
							case IO_FD:
							{
								builtin_stdin = in->param1.old_fd;
								break;
							}
							case IO_PIPE:
							{
								builtin_stdin = in->param1.pipe_fd[0];
								break;
							}
							
							case IO_FILE:
							{
								builtin_stdin=wopen( in->filename,
                                              in->param2.flags, OPEN_MASK );
								if( builtin_stdin == -1 )
								{
									debug( 1, 
										   FILE_ERROR,
										   in->filename.c_str() );
									wperror( L"open" );
								}
								else
								{
									close_stdin = 1;
								}
								
								break;
							}
	
							case IO_CLOSE:
							{
								/*
								  FIXME:

								  When
								  requesting
								  that
								  stdin
								  be
								  closed,
								  we
								  really
								  don't
								  do
								  anything. How
								  should
								  this
								  be
								  handled?
								 */
								builtin_stdin = -1;
								
								break;
							}
							
							default:
							{
								builtin_stdin=-1;
								debug( 1, 
									   _( L"Unknown input redirection type %d" ),
									   in->io_mode);
								break;
							}
						
						}
					}
				}
				else
				{
					builtin_stdin = pipe_read.param1.pipe_fd[0];
				}

				if( builtin_stdin == -1 )
				{
					exec_error=1;
					break;
				}
				else
				{
					int old_out = builtin_out_redirect;
					int old_err = builtin_err_redirect;

					/* 
					   Since this may be the foreground job, and since
					   a builtin may execute another foreground job,
					   we need to pretend to suspend this job while
					   running the builtin, in order to avoid a
					   situation where two jobs are running at once.

					   The reason this is done here, and not by the
					   relevant builtins, is that this way, the
					   builtin does not need to know what job it is
					   part of. It could probably figure that out by
					   walking the job list, but it seems more robust
					   to make exec handle things.
					*/
					
					builtin_push_io( parser, builtin_stdin );
					
					builtin_out_redirect = has_fd( j->io, 1 );
					builtin_err_redirect = has_fd( j->io, 2 );		

					fg = job_get_flag( j, JOB_FOREGROUND );
					job_set_flag( j, JOB_FOREGROUND, 0 );
					
					signal_unblock();
					
					p->status = builtin_run( parser, p->get_argv(), j->io );
					
					builtin_out_redirect=old_out;
					builtin_err_redirect=old_err;
					
					signal_block();
					
					/*
					  Restore the fg flag, which is temporarily set to
					  false during builtin execution so as not to confuse
					  some job-handling builtins.
					*/
					job_set_flag( j, JOB_FOREGROUND, fg );
				}
				
				/*
				  If stdin has been redirected, close the redirection
				  stream.
				*/
				if( close_stdin )
				{
					exec_close( builtin_stdin );
				}				
				break;				
			}
		}
		
		if( exec_error )
		{
			break;
		}
		
		switch( p->type )
		{

			case INTERNAL_BLOCK:
			case INTERNAL_FUNCTION:
			{
				int status = proc_get_last_status();
						
				/*
				  Handle output from a block or function. This usually
				  means do nothing, but in the case of pipes, we have
				  to buffer such io, since otherwise the internal pipe
				  buffer might overflow.
				*/
				if( !io_buffer )
				{
					/*
					  No buffer, so we exit directly. This means we
					  have to manually set the exit status.
					*/
					if( p->next == 0 )
					{
						proc_set_last_status( job_get_flag( j, JOB_NEGATE )?(!status):status);
					}
					p->completed = 1;
					break;
				}

				j->io = io_remove( j->io, io_buffer );
				
				io_buffer_read( io_buffer );
				
				if( io_buffer->param2.out_buffer->used != 0 )
				{
					pid = exec_fork();

					if( pid == 0 )
					{
						
						/*
						  This is the child process. Write out the contents of the pipeline.
						*/
						p->pid = getpid();
						setup_child_process( j, p );

						exec_write_and_exit(io_buffer->fd, 
											io_buffer->param2.out_buffer->buff,
											io_buffer->param2.out_buffer->used,
											status);
					}
					else
					{
						/* 
						   This is the parent process. Store away
						   information on the child, and possibly give
						   it control over the terminal.
						*/
						p->pid = pid;						
						set_child_group( j, p, 0 );
												
					}					
					
				}
				else
				{
					if( p->next == 0 )
					{
						proc_set_last_status( job_get_flag( j, JOB_NEGATE )?(!status):status);
					}
					p->completed = 1;
				}
				
				io_buffer_destroy( io_buffer );
				
				io_buffer=0;
				break;
				
			}


			case INTERNAL_BUFFER:
			{
		
				pid = exec_fork();
				
				if( pid == 0 )
				{
					/*
					  This is the child process. Write out the
					  contents of the pipeline.
					*/
					p->pid = getpid();
					setup_child_process( j, p );
					
					exec_write_and_exit( 1,
										 input_redirect->param2.out_buffer->buff, 
										 input_redirect->param2.out_buffer->used,
										 0);
				}
				else
				{
					/* 
					   This is the parent process. Store away
					   information on the child, and possibly give
					   it control over the terminal.
					*/
					p->pid = pid;						
					set_child_group( j, p, 0 );	
				}	

				break;				
			}
			
			case INTERNAL_BUILTIN:
			{
				int skip_fork;
				
				/*
				  Handle output from builtin commands. In the general
				  case, this means forking of a worker process, that
				  will write out the contents of the stdout and stderr
				  buffers to the correct file descriptor. Since
				  forking is expensive, fish tries to avoid it wehn
				  possible.
				*/

				/*
				  If a builtin didn't produce any output, and it is
				  not inside a pipeline, there is no need to fork
				*/
				skip_fork =
                    get_stdout_buffer().empty() &&
                    get_stderr_buffer().empty() &&
					!p->next;
	
				/*
				  If the output of a builtin is to be sent to an internal
				  buffer, there is no need to fork. This helps out the
				  performance quite a bit in complex completion code.
				*/

				io_data_t *io = io_get( j->io, 1 );
				int buffer_stdout = io && io->io_mode == IO_BUFFER;
				
				if( ( get_stderr_buffer().empty() ) && 
					( !p->next ) &&
					( ! get_stdout_buffer().empty() ) && 
					( buffer_stdout ) )
				{
					std::string res = wcs2string( get_stdout_buffer() );
					b_append( io->param2.out_buffer, res.c_str(), res.size() );
					skip_fork = 1;
				}

				for( io = j->io; io; io=io->next )
				{
					if( io->io_mode == IO_FILE && io->filename != L"/dev/null")
					{
						skip_fork = 0;
					}
				}
				
				if( skip_fork )
				{
					p->completed=1;
					if( p->next == 0 )
					{
						debug( 3, L"Set status of %ls to %d using short circut", j->command_cstr(), p->status );
						
						int status = p->status;
						proc_set_last_status( job_get_flag( j, JOB_NEGATE )?(!status):status );
					}
					break;
				}

				/*
				  Ok, unfortunatly, we have to do a real fork. Bummer.
				*/
								
				pid = exec_fork();
				if( pid == 0 )
				{

					/*
					  This is the child process. Setup redirections,
					  print correct output to stdout and stderr, and
					  then exit.
					*/
					p->pid = getpid();
					setup_child_process( j, p );
                    const wcstring &out = get_stdout_buffer(), &err = get_stderr_buffer();
					do_builtin_io( out.empty() ? NULL : out.c_str(), err.empty() ? NULL : err.c_str() );
					exit( p->status );
						
				}
				else
				{
					/* 
					   This is the parent process. Store away
					   information on the child, and possibly give
					   it control over the terminal.
					*/
					p->pid = pid;
						
					set_child_group( j, p, 0 );
										
				}					
				
				break;
			}
			
			case EXTERNAL:
			{
				pid = exec_fork();
				if( pid == 0 )
				{
					/*
					  This is the child process. 
					*/
					p->pid = getpid();
					setup_child_process( j, p );
					launch_process( p );
					
					/*
					  launch_process _never_ returns...
					*/
				}
				else
				{
					/* 
					   This is the parent process. Store away
					   information on the child, and possibly fice
					   it control over the terminal.
					*/
					p->pid = pid;

					set_child_group( j, p, 0 );
															
				}
				break;
			}
			
		}

		if( p->type == INTERNAL_BUILTIN )
			builtin_pop_io(parser);
				
		/* 
		   Close the pipe the current process uses to read from the
		   previous process_t
		*/
		if( pipe_read.param1.pipe_fd[0] >= 0 )
			exec_close( pipe_read.param1.pipe_fd[0] );
		/* 
		   Set up the pipe the next process uses to read from the
		   current process_t
		*/
		if( p->next )
			pipe_read.param1.pipe_fd[0] = mypipe[0];
		
		/* 
		   If there is a next process in the pipeline, close the
		   output end of the current pipe (the surrent child
		   subprocess already has a copy of the pipe - this makes sure
		   we don't leak file descriptors either in the shell or in
		   the children).
		*/
		if( p->next )
		{
			exec_close(mypipe[1]);
		}		
	}

	/*
	  The keepalive process is no longer needed, so we terminate it
	  with extreme prejudice
	*/
	if( needs_keepalive )
	{
		kill( keepalive.pid, SIGKILL );
	}
	
	signal_unblock();	

	debug( 3, L"Job is constructed" );

	j->io = io_remove( j->io, &pipe_read );

	for( tmp = parser.block_io; tmp; tmp=tmp->next )
		j->io = io_remove( j->io, tmp );
	
	job_set_flag( j, JOB_CONSTRUCTED, 1 );

	if( !job_get_flag( j, JOB_FOREGROUND ) )
	{
		proc_last_bg_pid = j->pgid;
	}

	if( !exec_error )
	{
		job_continue (j, 0);
	}
	
}


static int exec_subshell_internal( const wcstring &cmd, wcstring_list_t *lst )
{
	char *begin, *end;
	char z=0;
	int prev_subshell = is_subshell;
	int status, prev_status;
	io_data_t *io_buffer;
	char sep=0;
	
	const env_var_t ifs = env_get_string(L"IFS");

	if( ! ifs.missing_or_empty() )
	{
		if( ifs.at(0) < 128 )
		{
			sep = '\n';//ifs[0];
		}
		else
		{
			sep = 0;
			debug( 0, L"Warning - invalid command substitution separator '%lc'. Please change the firsta character of IFS", ifs[0] );
		}
		
	}
	
	is_subshell=1;	
	io_buffer= io_buffer_create( 0 );
	
	prev_status = proc_get_last_status();
	
    parser_t &parser = parser_t::principal_parser();
	if( parser.eval( cmd, io_buffer, SUBST ) )
	{
		status = -1;
	}
	else
	{
		status = proc_get_last_status();
	}
	
	io_buffer_read( io_buffer );
		
	proc_set_last_status( prev_status );
	
	is_subshell = prev_subshell;
	
	b_append( io_buffer->param2.out_buffer, &z, 1 );
	
	begin=end=io_buffer->param2.out_buffer->buff;	

	if( lst )
	{
		while( 1 )
		{
			if( *end == 0 )
			{
				if( begin != end )
				{
					wchar_t *el = str2wcs( begin );
					if( el )
					{
						lst->push_back(el);

						free(el);
					}
					else
					{
						debug( 2, L"Got null string on line %d of file %s", __LINE__, __FILE__ );
					}
				}				
				io_buffer_destroy( io_buffer );
				
				return status;
			}
			else if( *end == sep )
			{
				wchar_t *el;
				*end=0;
				el = str2wcs( begin );
				if( el )
				{
                    lst->push_back(el);

					free(el);
				}
				else
				{
					debug( 2, L"Got null string on line %d of file %s", __LINE__, __FILE__ );
				}
				begin = end+1;
			}
			end++;
		}
	}
	
	io_buffer_destroy( io_buffer );

	return status;	
}

int exec_subshell( const wcstring &cmd, std::vector<wcstring> &outputs )
{
    return exec_subshell_internal(cmd, &outputs);
}

__warn_unused int exec_subshell( const wcstring &cmd )
{
    return exec_subshell_internal(cmd, NULL);
}