Send input to a program and get control back

Question

Hello,

I have been stuck on this for some time. Let's say I have a C program like the following. I want to be able to send this program some string and get the control after that. If I do:

--> cat myfile | myprogram
or
--> echo "0123" | myprogram
or
--> myprogram < myfile
I get the ouput (myfile contains "0123")
30 31 32 33

Using the -n option raises a segfault
--> echo -n mystring | ./test
zsh: done echo -n "0123" |
zsh: segmentation fault ./test

I also tried with a named pipe, but it didn't work either.

I would like to be able to do something like cat myfile | myprogram and get back the control so that I can type other characters.

  1 #include  <stdlib.h>
  2 #include  <stdio.h>
  3 
  4 int main (int argc, char *argv[]) {
  6   int i = 0, j;
  7   unsigned char buf[512];
  8   unsigned char x;
  9 
 10   while ((x = getchar()) != '\n') {
 11     buf[i] = x;
 12     i++;
 13   }
 14 
 16   for (j = 0; j < i; j++) {
 17     printf("%x ", buf[j]);
 18   }
 19   printf ( "\n" );
 20 
 21   return EXIT_SUCCESS;
 22 }  // end of function main

Answer 1

In this example I use tail -f, not your C program

 mkfifo /tmp/pipe   # Open Pipe
 tail -f /tmp/pipe &    #  Start your program and put it into the background

Now you also can send data to your program that runs in the background

 echo "foobar" > /tmp/pipe

I hope this helps?

Answer 2

You could modify your program to accept 1 null character then continue on...it might work:

replace line 10 with something like

while (TRUE)
{
    x = getchar();
    if (x == '\n')
        break;
    if (x == '\0')
    {
        if (seen)
            break;
        seen = TRUE;
    }
...