execve(“/bin/sh”, 0, 0); in a pipe

Question

I have the following example program:

#include 

int
main(int argc, char ** argv){
    char buf[100];

    printf(\"Please enter your name: \");
          


        

Answer 1

You can run your program without any modifications like this:

(echo -e 'testName\n'; cat ) | ./a.out

This way you ensure that your program's standard input doesn't end after what echo outputs. Instead, cat continues to supply input to your program. The source of that subsequent input is your terminal since this is where cat reads from.

Here's an example session:

bash-3.2$ cc stdin_shell.c 
bash-3.2$ (echo -e 'testName\n'; cat ) | ./a.out 
Please enter your name: warning: this program uses gets(), which is unsafe.
Hello "testName"
pwd
/home/user/stackoverflow/stdin_shell_question
ls -l
total 32
-rwxr-xr-x  1 user  group  9024 Dec 14 18:53 a.out
-rw-r--r--  1 user  group   216 Dec 14 18:52 stdin_shell.c
ps -p $$
  PID TTY           TIME CMD
93759 ttys000    0:00.01 (sh)
exit

bash-3.2$

Note that because shell's standard input is not connected to a terminal, sh thinks it is not executed interactively and hence does not display the prompt. You can type your commands normally, though.