Cannot correctly connect multi-stage C command pipe (among others) (FYI: a lot of code) Post: 302787955

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Homework and Emergencies Homework & Coursework Questions Cannot correctly connect multi-stage C command pipe (among others) (FYI: a lot of code) Post 302787955 by kowit010 on Sunday 31st of March 2013 02:12:59 PM

03-31-2013

Registered User

Re:

Yeah, I know, sorry the code is so huge, I guess I had to post the whole code so the mods don't come down on me for not filling out the whole thread template, but anyway... I wish I had time to simplify the code, now I'm just trying to get this thing going. I changed the code to this (just including the problem area in the "create_command_process" function):

Code:

if(childpid=fork())//if more than one process, and this is the parent process....
 {
  if((cmd_pids[i]=(int)childpid)==-1)//did it fork correctly?
  {
   perror("Error forking!");
   exit(666);
  }
  close(prev[0]);//close previous filedescriptor in
  close(prev[1]);//close previous filedescriptor out
  close(curr[0]);
  close(curr[1]);
 }
 else
 {
  if(prev[1]!=-1)//if previous pipe has a valid item
  {
      dup2(prev[0],0);
      dup2(prev[1],1);
      close(prev[0]);
      close(prev[1]);
  }
  if(curr[0]!=-1)//if current pipe has a valid item
  {
      dup2(curr[0],0);
      dup2(curr[1],1);
      close(curr[0]);
      close(curr[1]);
  }
    execvp(test,argvector);//execute the process....
 }

When I run it with "ls | wc", absolute NO output to the shell console comes back (even though it's writing stuff to my logfile). I will work on this some more, but I don't know if this means it's working now? Aren't I like supposed to get a set of numbers back for "ls | wc"? (running it in shell spits out "16 16 150" in my current folder). Then again, the assignment description says this, and I quote:

"　
The standard output stream is used and used only for printing command execution results.
"

So I take this to mean I shouldn't have to worry enough about it printing anything straight to the console?

---------- Post updated at 01:12 PM ---------- Previous update was at 01:11 PM ----------

Quote:

Originally Posted by Corona688

Also, exit(666) makes no sense. It only takes numbers 1-127.

Oh, really? I didn't know that. I just heard that any non-zero number fed into an exit() call indicated failure so I use 666 to be a wise guy for obvious reasons, bahahaha. I'll change it, though, to be something in that valid range. Thanks.

kowit010

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truncate

TRUNCATE(1)							   User Commands						       TRUNCATE(1)

NAME

       truncate - shrink or extend the size of a file to the specified size

SYNOPSIS

       truncate OPTION... FILE...

DESCRIPTION

       Shrink or extend the size of each FILE to the specified size

       A FILE argument that does not exist is created.

       If  a  FILE  is	larger than the specified size, the extra data is lost.  If a FILE is shorter, it is extended and the extended part (hole)
       reads as zero bytes.

       Mandatory arguments to long options are mandatory for short options too.

       -c, --no-create
	      do not create any files

       -o, --io-blocks
	      treat SIZE as number of IO blocks instead of bytes

       -r, --reference=RFILE
	      base size on RFILE

       -s, --size=SIZE
	      set or adjust the file size by SIZE bytes

       --help display this help and exit

       --version
	      output version information and exit

       SIZE is an integer and optional unit (example: 10M is 10*1024*1024).  Units are K, M, G, T, P, E, Z, Y (powers of  1024)  or  KB,  MB,  ...
       (powers of 1000).

       SIZE  may also be prefixed by one of the following modifying characters: '+' extend by, '-' reduce by, '<' at most, '>' at least, '/' round
       down to multiple of, '%' round up to multiple of.

       GNU  coreutils  online  help:  <http://www.gnu.org/software/coreutils/>	Report	truncate  translation  bugs   to   <http://translationpro-
       ject.org/team/>

AUTHOR

       Written by Padraig Brady.

COPYRIGHT

       Copyright (C) 2013 Free Software Foundation, Inc.  License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>.
       This is free software: you are free to change and redistribute it.  There is NO WARRANTY, to the extent permitted by law.

SEE ALSO

       dd(1), truncate(2), ftruncate(2)

       The  full  documentation  for truncate is maintained as a Texinfo manual.  If the info and truncate programs are properly installed at your
       site, the command

	      info coreutils 'truncate invocation'

       should give you access to the complete manual.

GNU coreutils 8.22						     June 2014							       TRUNCATE(1)