Shell Implementation not working correctly


 
Thread Tools Search this Thread
Top Forums Programming Shell Implementation not working correctly
# 8  
Old 11-07-2007
Yes, tmpin will be 3, and tmpout will be 4. These will both be open file descriptors that the child processes will inherit.
# 9  
Old 11-07-2007
Ok yes i see. I had a different idea of what dup did, i have only been doing this Unix stuff for about a week. But in reallity it wont really change my program to close those because they will just close when the child process closes, its just messy. The real question is why my stupid pipes are not working. It Makes No Sense! Smilie. But thanks man.
# 10  
Old 11-07-2007
I'll give it a compile and have a look.
# 11  
Old 11-07-2007
Oh, and another peeve of mine, don't use C++ comments in C code. Smilie

EDIT: Oops, this is actually C++ code as the for statement defines the variable.

Last edited by porter; 11-07-2007 at 04:39 PM..
# 12  
Old 11-07-2007
man pipe

Code:
fdin=fdpipe[0];
fdout=fdpipe[1];

the first element is the read end, the second element is the write end of the pipe.

On some platforms(Solaris) pipes are bidirectional, but this is classical UNIX.

Also, you need to reap (with some form of wait) all the pids you get back from fork, not just the last one, else you end up with zombies, so I would expect you to capture all those pids.

Last edited by porter; 11-07-2007 at 04:45 PM..
# 13  
Old 11-08-2007
Yes my good man. But if you look at the drawing and think about it the output of the command that is going to run will need to be written to the input of next command. So making the output write to that file will pipe over to the input file and the 0th descriptor will be set to that at the top of the loop. Just look at the pics and think about it and you will get it.
# 14  
Old 11-08-2007
Quote:
Originally Posted by AirBronto
Just look at the pics and think about it and you will get it.
Perhaps, but the difference between you and me is I have a working pipeline from your code with that small change.

Code:
$ uname -a
SunOS foobar 5.7 Generic_106541-08 sun4c sparc SUNW,Sun_4_50
$ /usr/local/bin/gcc ab.c -o ab
$ echo "fred" | ./ab
fdout=6,fdin=5
pid=274,tmpin=3,tmpout=4
fdout=6,fdin=5
pid=275,tmpin=3,tmpout=4
0+1 records in
0+1 records out
0+1 records in
0+1 records out
fdout=6,fdin=5
pid=276,tmpin=3,tmpout=4
0+1 records in
0+1 records out
pid=277,tmpin=3,tmpout=4
fred
0+1 records in
0+1 records out

and the complete source should look very familiar....

Code:
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/wait.h>
#include <stdio.h>
#include <unistd.h>
#include <errno.h>
#include <stdlib.h>
#include <fcntl.h>

struct cmd
{
  char **_arguments;
};

char *args[]={
	"dd",NULL,
	"dd",NULL,
	"dd",NULL,
	"dd",NULL
};

struct cmd cmdList[]={
	{args+0},
	{args+2},
	{args+4},
	{args+6}
};

struct cmd *_simpleCommands[]={
	cmdList+0,
	cmdList+1,
	cmdList+2,
	cmdList+3
};

char *_inputFile;
char *_outFile;

int main(int argc,char **argv)
{
int _background=0;
int _numberOfSimpleCommands=(sizeof(cmdList)
									/sizeof(cmdList[0]));
	int tmpin=dup(0);
	int tmpout=dup(1);
	int ret=-1;
	int fdout=-1;
	int fdin=-1;
	int i;
	int rc=0;

	if(_inputFile)
	{
	   fdin = open(_inputFile, O_RDONLY | O_CREAT, S_IREAD | S_IWRITE);
	}
	else
	{
	   fdin=dup(tmpin);
	}

	for (i = 0; i < _numberOfSimpleCommands; i++)
	{
	   rc=dup2(fdin, 0); if (rc==-1) perror("dup2(fdin)");
	   close(fdin); fdin=-1;

	   if(i == _numberOfSimpleCommands-1) 
	   {
	      if(_outFile)
	      {
	         fdout=open(_outFile, O_WRONLY | O_CREAT, S_IREAD | S_IWRITE);
	      }
	      else
	      {  
	         fdout=dup(tmpout);
	      }
	   }
	   else
	   {
	      int fdpipe[2];
	      pipe(fdpipe);
          fdin=fdpipe[0];
          fdout=fdpipe[1];

			fprintf(stderr,"fdout=%d,fdin=%d\n",fdout,fdin);
	    }

	    rc=dup2(fdout,1); if (rc==-1) perror("dup2(fdout)");

	    close(fdout); fdout=-1;

	    ret = fork();
	    if(ret==0)
	    {
			fprintf(stderr,"pid=%d,tmpin=%d,tmpout=%d\n",
					getpid(),tmpin,tmpout);			
			rc=close(tmpin); if (rc) perror("close(tmpin)");
			rc=close(tmpout); if (rc) perror("close(tmpout)");

			execvp( (*_simpleCommands)[i]._arguments[0],
					(*_simpleCommands)[i]._arguments);

	       	perror("execvp");
	       	exit(1);
	     }
	}

	rc=dup2(tmpin, 0); if (rc==-1) perror("dup2(tmpin,0)");
	rc=dup2(tmpout, 1); if (rc==-1) perror("dup2(tmpin,0)");
	close(tmpin);
	close(tmpout);
	
	if(!_background)
	{
		waitpid(ret, 0, 0);
	}

    return 0;
}

Login or Register to Ask a Question

Previous Thread | Next Thread

10 More Discussions You Might Find Interesting

1. UNIX for Beginners Questions & Answers

Are the brains of the UNIXoid working correctly?

Today I saw the topic. sum-even-numbers-1-100 At that time, it was already closed but not the point. Other thoughts came to mind. All newcomers to Haskell are afraid that when they study it, their brains will turn inside out. I did not notice anything like that. And all because the brains of all... (4 Replies)
Discussion started by: nezabudka
4 Replies

2. UNIX for Dummies Questions & Answers

vnc No Longer Working Correctly

Hello All, Yesterday, all day, I was using x11vnc and vncviewer to connect to a server. But today for some reason it is not working. I don't remember changing any settings or anything like that, but because it stopped working correctly I guess something has...? I'm issuing the exact same... (0 Replies)
Discussion started by: mrm5102
0 Replies

3. Shell Programming and Scripting

awk not working correctly

Hi I am attempting to right a script which will read a table and extract specfic information. LASTFAILEDJOB=/usr/openv/netbackup/scripts/GB-LDN/Junaid/temp_files/lastfailedjob cat /usr/openv/netbackup/scripts/GB-LDN/Junaid/temp_files/lastfailedjob 237308646 If i run the following... (5 Replies)
Discussion started by: Junes
5 Replies

4. UNIX for Dummies Questions & Answers

Grep Regexp not working correctly

Consider the following code: grep -o -e '^STEAM_::\d+$' workfile3.tmp A sample format of a valid string for the regexp would be: STEAM_0:1:12345678 Here is an example line from the workfile3.tmp file: 465:L 01/02/2012 - 00:05:33: "Spartan1-1-7<8><STEAM_0:1:47539638><>" connected No... (2 Replies)
Discussion started by: spinner0205
2 Replies

5. Shell Programming and Scripting

rsync is not correctly working

We are using Red Hat linux system. I am transferring my rman backup files to another server. Here is the command i am using to transfer the files. /usr/bin/rsync -avpP --delete /xyz/xyz/ 99.99.999.99::db110bkp Here is the rsync version. >rsync --version rsync version 3.0.6 ... (1 Reply)
Discussion started by: govindts
1 Replies

6. Shell Programming and Scripting

Find cmd not working correctly in script

I am trying to copy 2 types of files so I can archive them. I tested with a set of commands: touch -t $(date -d "-60 day" +%Y%m%d) WORKDIR/REF find TARGETDIR/ -type f -maxdepth 1 -iname \*.out\* -or -iname \*.log\* ! -newer WORKDIR/REF -exec ls -l {} \; This correctly lists any files in the... (2 Replies)
Discussion started by: prismtx
2 Replies

7. UNIX for Dummies Questions & Answers

grep -A switch not working correctly with -m

egrep -A 7 -m 2 -h 'Date:|Time:' *.html this is showing only 2 line after the context of the 2nd found match. Is this a bug in grep? egrep -A 7 -m 2 -h 'Time:' *.html - this works correctly (2 Replies)
Discussion started by: zer0
2 Replies

8. Shell Programming and Scripting

Variable not working correctly.

Hi, I have a script where I am trying to set a local variable using the following, MYVAR="$NAME"_"$NAME2".txt where say, NAME = one NAME2 = two so I want the output one_two.txt but what I am getting is, two.txt basically the $NAME2 is overwriting, what am I doing wrong? ... (3 Replies)
Discussion started by: walsh_j
3 Replies

9. Shell Programming and Scripting

if not working correctly

Anyone have an idea why this if statement does not work correctly? "test2.sh" 18 lines, 386 characters #!/usr/bin/sh WARNING=80 CRITICAL=95 check_it() { if ] || ];then echo "YES ] || ]" else echo "NO ] || ]" fi } check_it 80.1 check_it 81.1 (3 Replies)
Discussion started by: 2dumb
3 Replies

10. UNIX for Dummies Questions & Answers

Script not working correctly

I have a simple script that I want to run every 30 minutes but only when I execute it. I don't want it to be a crontab job. so i have for example date ls -l who sleep 1800 The first time it executes correctly but after the first time it nevers execute back again. It should execute after... (2 Replies)
Discussion started by: elchalateco
2 Replies
Login or Register to Ask a Question