i really stuck in programming a tool with bidirectional process communication (popen(cmd, "rw") ... something like that ;-)).
Here is the code:
intersting are only the last 10 lines. I try to write to factor, then read, than write again (...) until 0 is given. This wont work, because read(p_stdout[READ], ....) always blocks the programm, waiting for some better waeather are someso. I tried to use fsync() between write and read, but it didnt help. Only fclose() solve the problem, but if p_stdin[WRITE] is closed, i can only iterate the loop one times.
Is there any possibility that a Stream Read and Write queues will interchange messages of any kind. If so what are the different possiblites and under what circumstances ?
Thanks in advance. (4 Replies)
I am programming some data loader of oracle with unix c, when I find new data file, then read it to database and delete it. but one issue, if the file is in process of creating, not been closed yet. I will read zero or part of data content, this will cause problem. I want to know whether some unix... (2 Replies)
Hi Everyone,
Good day.
Scenario:
2 unix servers -- A (SunOS) and B (AIX)
I have an ftp script to sftp 30 files from A to B which happen almost instantaneously i.e 30 sftp's happen at the same time.
Some of these sftp's fail with the following error:
ssh_exchange_identification: Connection... (1 Reply)
Can you help me ?
I want to write a program ,which can open a input file (input.txt) and run as child process ,then write to output file (output.txt).......
char inFile="input.txt";
char outFile="output.txt";
int main(int argc, char **argv)
{
pid_t pid=1;
int no=0; // no. of... (5 Replies)
Hi,
I have file which contains information written in blocks (every block is different). Is it possible to read every block one by one to another file (one block per file).
The input is something like this
<block1>
<empty line>
<block2>
<empty line>
...
...
...
<block25>
<empty... (0 Replies)
Hi
I used this command:
mplayer http://host/axis-cgi/mjpg/video.cgi -user root -passwd root \
-cache 1024 -fps 25.0 -nosound -vc ffh264 \
-demuxer 3 -dumpstream -dumpfile output.avi It's ok but...
Video Playing is very fast! Why? Is it a synch problem?
What parameter I have to use for... (1 Reply)
I'm Unix. I'm looking at "df" on Unix now and below is an example. It's lists the filesystems out in 512-blocks, I need this in 4k blocks. Is there a way to do this in Unix or do I manually convert and how?
So for container 1 there is 7,340,032 in size in 512-blocks. What would the 4k block be... (2 Replies)
Hello,
I have a file like this:
FILE.TXT:
(define argc :: int)
(assert ( > argc 1))
(assert ( = argc 1))
<check>
#
(define c :: float)
(assert ( > c 0))
(assert ( = c 0))
<check>
#
now, i want to separate each block('#' is the delimeter), make them separate files, and then send them as... (5 Replies)
I have a script that takes 2 parameters (say) as mandatory
script1.sh a b
The 3rd parameter can be filename which it should process or it can come through a pipeline stream
The script should work both ways:
script1.sh a b filec
or cat filec | script1.sh a b
How to put logic in the... (1 Reply)
Hello,
Searched for a while and found some "line-to-column" script. My case is similar but with multiple fields each row:
S02 Length Per
S02 7043 3.864
S02 54477 29.89
S02 104841 57.52
S03 Length Per
S03 1150 0.835
S03 1321 0.96
S03 ... (9 Replies)
Discussion started by: yifangt
9 Replies
LEARN ABOUT FREEBSD
popen
POPEN(3) BSD Library Functions Manual POPEN(3)NAME
popen, pclose -- process I/O
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <stdio.h>
FILE *
popen(const char *command, const char *type);
int
pclose(FILE *stream);
DESCRIPTION
The popen() function ``opens'' a process by creating a bidirectional pipe forking, and invoking the shell. Any streams opened by previous
popen() calls in the parent process are closed in the new child process. Historically, popen() was implemented with a unidirectional pipe;
hence many implementations of popen() only allow the type argument to specify reading or writing, not both. Since popen() is now implemented
using a bidirectional pipe, the type argument may request a bidirectional data flow. The type argument is a pointer to a null-terminated
string which must be 'r' for reading, 'w' for writing, or 'r+' for reading and writing.
A letter 'e' may be appended to that to request that the underlying file descriptor be set close-on-exec.
The command argument is a pointer to a null-terminated string containing a shell command line. This command is passed to /bin/sh using the
-c flag; interpretation, if any, is performed by the shell.
The return value from popen() is a normal standard I/O stream in all respects save that it must be closed with pclose() rather than fclose().
Writing to such a stream writes to the standard input of the command; the command's standard output is the same as that of the process that
called popen(), unless this is altered by the command itself. Conversely, reading from a ``popened'' stream reads the command's standard
output, and the command's standard input is the same as that of the process that called popen().
Note that output popen() streams are fully buffered by default.
The pclose() function waits for the associated process to terminate and returns the exit status of the command as returned by wait4(2).
RETURN VALUES
The popen() function returns NULL if the fork(2) or pipe(2) calls fail, or if it cannot allocate memory.
The pclose() function returns -1 if stream is not associated with a ``popened'' command, if stream already ``pclosed'', or if wait4(2)
returns an error.
ERRORS
The popen() function does not reliably set errno.
SEE ALSO sh(1), fork(2), pipe(2), wait4(2), fclose(3), fflush(3), fopen(3), stdio(3), system(3)HISTORY
A popen() and a pclose() function appeared in Version 7 AT&T UNIX.
Bidirectional functionality was added in FreeBSD 2.2.6.
BUGS
Since the standard input of a command opened for reading shares its seek offset with the process that called popen(), if the original process
has done a buffered read, the command's input position may not be as expected. Similarly, the output from a command opened for writing may
become intermingled with that of the original process. The latter can be avoided by calling fflush(3) before popen().
Failure to execute the shell is indistinguishable from the shell's failure to execute command, or an immediate exit of the command. The only
hint is an exit status of 127.
The popen() function always calls sh(1), never calls csh(1).
BSD May 20, 2013 BSD