Ok. I'am finally beginning to see where the word emulator comes in now. So apart from isatty(), are there a number of other calls to watch for, is there documentation online for this.
Strange, but I made a console application and redirected the stdout and stderr the way you instructed, but to a file and it worked just fine. How did the isatty() function not pickup on this?
Strange, but I made a console application and redirected the stdout and stderr the way you instructed, but to a file and it worked just fine. How did the isatty() function not pickup on this?
Most utilities don't care, and shouldn't care. Their output is expected to be piped and redirected in creative ways. Only things like interactive editors and login systems check isatty().
Thanks for the help so far. With the time I have got, I managed to put together the app this far. Currently my only problem is I cant seem to send any keyboard input to the child process program. Please take a look at my code and advice.
Code:
#include <sys/wait.h>
#include <assert.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <error.h>
int main(int argc, char *argv[])
{
int MAXLINE = 2000;
int fd1[2];
int fd2[2];
pid_t pid;
char line[MAXLINE];
char *PROGRAM_B_INPUT= "fake input\n";
char *PROGRAM_B = argv[1];
error(0,0,"Starting [%s]...", PROGRAM_B);
if ( (pipe(fd1) < 0) || (pipe(fd2) < 0) )
{
error(0,0,"PIPE ERROR");
return -2;
}
if ( (pid = fork()) < 0 )
{
error(0,0,"FORK ERROR");
return -3;
}
else if (pid == 0) // CHILD PROCESS
{
close(fd1[1]);
close(fd2[0]);
if (dup2(fd1[0], STDIN_FILENO) != STDIN_FILENO)
{
error(0,0,"-- CHILD -- dup2 error to stdin");
}
close(fd1[0]);
if (dup2(fd2[1], STDOUT_FILENO) != STDOUT_FILENO)
{
error(0,0,"-- CHILD -- dup2 error to stdout");
}
close(fd2[1]);
if ( execl(PROGRAM_B, PROGRAM_B, (char *)0) < 0 )
{
error(0,0,"-- CHILD -- system error");
perror("ERROR DEFN : ");
return -4;
}
return 0;
}
else // PARENT PROCESS
{
int rv;
close(fd1[0]);
close(fd2[1]);
if ( write(fd1[1], PROGRAM_B_INPUT, strlen(PROGRAM_B_INPUT) ) != strlen(PROGRAM_B_INPUT) )
{
error(0,0,"READ ERROR FROM PIPE");
}
if ( (rv = read(fd2[0], line, MAXLINE)) < 0 )
{
error(0,0,"READ ERROR FROM PIPE");
}
else if (rv == 0)
{
error(0,0,"Child Closed Pipe");
return 0;
}
error(0,0,"OUTPUT of PROGRAM B is: \n%s", line);
return 0;
}
return 0;
}
You having put it in quote tags instead of code tags means I can't even quote it to get the program with sane indentation and must do it all by hand.. I'll take a look ati t...
---------- Post updated at 04:53 PM ---------- Previous update was at 04:45 PM ----------
Your program actually worked without modification, first try:
Code:
$ ./a.out /bin/cat
./a.out: Starting [/bin/cat]...
./a.out: OUTPUT of PROGRAM B is:
fake input
��
$
...though you forget to null-terminate your read string, read doesn't do that for you!
Code:
...
line[rv]='\0';
error(0,0,"OUTPUT of PROGRAM B is: \n%s", line);
Code:
$ ./a.out /bin/cat
$ ./a.out /bin/cat
./a.out: Starting [/bin/cat]...
./a.out: OUTPUT of PROGRAM B is:
fake input
$
And depending on your system the pipe may actually buffer and wait forever. You should close() the pipe after you're done writing to it, to force it to send the stuff along before you try and read() from the other pipe.
Sorry about the QUOTE tags, just now seen the CODE one.
I suspected something of the sort, but didn't know whether it was a \n escape that was needed or something else. I guess now my biggest challenge is how to continuously send and receive text from a more interactive program. I was testing it with passwd and was unable to control the input and output correctly. Please help me understand how I can achieve this successfully. I suspect some looping will be required, don't have a clue where to start with that with all the pipe logic.
The only time I received an isatty related error was with a few interactive types of programs like top. It said that the tty check failed, just as you said some of them would. passwd on the other hand launches well and requests for some input. getting it this input and retrieving the next output is proving to be the challenge. I hope you are not saying that this method completely cannot work with interactive programs. If it is possible, I would be grateful for some pointers on how to go about it.
Hi, I was just wondering how to distinguish between the two terms:
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2. shell command line
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