How do I use a pipe to redirect the output of one command to the input of another?

Question

I have a program which sends text to an LED sign.

prismcom.exe

To use the program to send \"Hello\":

prismcom.exe usb Hello

Answer 1

Not sure if you are coding these programs, but this is a simple example of how you'd do it.

program1.c

#include 
int main (int argc, char * argv[] ) {
    printf("%s", argv[1]); 
    return 0;
}

rgx.cpp

#include 
#include 
#include 
using namespace std;
int main (int argc, char * argv[] ) {
    char input[200];
    fgets(input,200,stdin);
    string s(input)
    smatch m;
    string reg_exp(argv[1]);
    regex e(reg_exp);
    while (regex_search (s,m,e)) {
      for (auto x:m) cout << x << " ";
      cout << endl;
      s = m.suffix().str();
    }
    return 0;
}

Compile both then run program1.exe "this subject has a submarine as a subsequence" | rgx.exe "\b(sub)([^ ]*)"

The | operator simply redirects the output of program1's printf operation from the stdout stream to the stdin stream whereby it's sitting there waiting for rgx.exe to pick up.