Capture stdout from multiple processes Post: 302546992

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Top Forums Programming Capture stdout from multiple processes Post 302546992 by dvales on Friday 12th of August 2011 08:31:22 PM

08-12-2011

Registered User

Capture stdout from multiple processes

I have a number of binaries which I currenlty have no control over. They alright data to stdout. I would like to kick off any number of these binaries and capture and process their stdout. Doing this for one process is straight forward for example - comments and error checking removed for simplicity

Code:

pid_t pid;
int	commpipe[2];
char buf[BUFSIZE];

pipe(commpipe)
 
pid=fork();

 if(pid){
    dup2(commpipe[0],0);
    close(commpipe[0]);
    while ( fgets ( buf, BUFSIZE, stdin ) )
    { processBuffer ( buf );
 } else{
    dup2(commpipe[1],1); 
   close(commpipe[0]);
    setvbuf(stdout,(char*)NULL,_IONBF,0); 
   execl("child","child",NULL) 	
}

I would run the above from a separate thread. This works fine for one process, if I attempt to repeat the above for a secoind process. the output of the 2 process is intermingled. I can solve the stdin side by not removing the dup2 call in the parent and reading directly from the read side of the pipe i.e. fgets( buf, BUFSIZE, stdin). But the data is still intermingled since it is the same stdout.
I can close stdout before forking but then I only get the output from one process.

The goal is to have a separate thread read the stdout of each process Any help will be appreciated

Thanks in advance

I'm sure there is away to do it

Last edited by zxmaus; 08-12-2011 at 11:40 PM.. Reason: added code tags

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LEARN ABOUT SUNOS

pid

pid(n)                                                         Tcl Built-In Commands                                                        pid(n)

__________________________________________________________________________________________________________________________________________________

NAME

       pid - Retrieve process identifiers

SYNOPSIS

       pid ?fileId?
_________________________________________________________________

DESCRIPTION

       If  the  fileId  argument is given then it should normally refer to a process pipeline created with the open command.  In this case the pid
       command will return a list whose elements are the process identifiers of all the processes in the pipeline, in order.   The  list  will  be
       empty if fileId refers to an open file that is not a process pipeline.  If no fileId argument is given then pid returns the process identi-
       fier of the current process.  All process identifiers are returned as decimal strings.

EXAMPLE

       Print process information about the processes in a pipeline using the SysV ps program before reading the output of that pipeline:

              set pipeline [open "| zcat somefile.gz | grep foobar | sort -u"]
              # Print process information
              exec ps -fp [pid $pipeline] >@stdout
              # Print a separator and then the output of the pipeline
              puts [string repeat - 70]
              puts [read $pipeline]
              close $pipeline

SEE ALSO

       exec(n), open(n)

KEYWORDS

       file, pipeline, process identifier

Tcl                                                                     7.0                                                                 pid(n)

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