What do you see when you execute \"pipe1\" ? Why? Modify the program pipe1.cpp t

Question

What do you see when you execute "pipe1" ? Why?
Modify the program pipe1.cpp to pipe1a.cpp so that it accepts a command (e.g. "ls -l") from the keyboard. For example, when you execute "./pipe1a ps -auxw", it should give you the same output as pipe1.cpp.
(Hint: Use string functions strcpy() and strcat() to store the commands in a buffer. Your main function should be like: int main( int argc, char *argv[] ) )

You can also send output to an external program via a pipe. Try the following program:

What do you see when you execute "pipe2" ? Why?
Modify the program so that it prints out the first three words of the sentence in reverse by making use of awk (see lab 2) (i.e. 'If said, Arnod....).

  //pipe1.cpp  #include <unistd.h>  #include <stdlib.h>  #include <string.h>  #include <stdio.h>  #include <iostream>    using namespace std;    int main()  {    FILE *fpi;                            //for reading a pipe       char buffer[BUFSIZ+1];                //BUFSIZ defined in <stdio.h>        int chars_read;    memset ( buffer, 0,sizeof(buffer));   //clear buffer    fpi = popen ( "ps -auxw", "r" );      //pipe to command "ps -auxw"    if ( fpi != NULL ) {      //read data from pipe into buffer      chars_read = fread(buffer, sizeof(char), BUFSIZ, fpi );        if ( chars_read > 0 )        cout << "Output from pipe: " << buffer << endl;      pclose ( fpi );                     //close the pipe      return 0;     }      return 1;  }  

Explanation / Answer

What do you see when you execute "pipe1" ? Why??

The pipe1 will execute the command ps as the command is passed to the process. using popen().

And the modified version of the same which takes the parameters dynamically is:

//pipe1.cpp
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <stdio.h>
#include <iostream>

using namespace std;

int main( int argc, char *argv[] )
{
FILE *fpi; //for reading a pipe

char buffer[BUFSIZ+1]; //BUFSIZ defined in <stdio.h>
  
int chars_read;
strcpy(buffer, argv[1]);   //Copies the first parameter to buffer.
for(int i = 2; i < argc; i++)   //Copies all the remaining parameters with space appended.
{
    strcat(buffer, " ");
    strcat(buffer, argv[i]);
}  
//cout << buffer << endl;   
fpi = popen ( buffer, "r" ); //pipe to command "ps -auxw"
memset ( buffer, 0,sizeof(buffer)); //clear buffer
if ( fpi != NULL ) {
//read data from pipe into buffer
chars_read = fread(buffer, sizeof(char), BUFSIZ, fpi );
if ( chars_read > 0 )
cout << "Output from pipe: " << buffer << endl;
pclose ( fpi ); //close the pipe
return 0;
}

return 1;
}

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