Multi tool use

Entering password into terminal through c

I searched for this question and could only find python variants. If this is a duplicate apologies upfront.

I'm trying to write a script in c that auto setup systems so that I don't have too manually do it on heaps of computers. For part of the script I need to enter a password.

stdin

bash

sudo

bash

2 Answers
2

If you have access to the terminal, why not use bash for these setups? In both instances of C, or bash, if you're accessing high privilege level areas, you'll need privilege access. The thing you'd be looking for would be a sudo command. It'll prompt you for the password prior to running it, and is just ran as follows:

sudo someExecutable


Some programs (that prompts for password) use isatty(STDIN_FILENO) call for ensuring that password is typed via terminal.

isatty(STDIN_FILENO)

In that case it not possible use normal pipes for sending password to the program.

For those programs, you can create a pseudo terminal, that is used instead of a pipe. Example:

void test(void)
{
const int fdm = posix_openpt(O_RDWR | O_NOCTTY);
if (fdm != -1)
{
char name[100];
unlockpt(fdm);
ptsname_r(fdm, name, sizeof(name));

const int fds = open(name, O_RDWR | O_NOCTTY);
if (fds != -1)
{
const pid_t child_pid = fork();

if (child_pid == -1)
{
// TODO: Error handling
}
else if (child_pid == 0)
{
dup2(fds, STDIN_FILENO);
dup2(fds, STDOUT_FILENO);
close(fds);
close(fdm);
execl("/sbin/program_that_requires_password_from_terminal", "blabla", (char*) NULL);
}
else
{
const char password = "mypasswordn";
int status;
close(fds);
// TODO: wait prompt from the program by reading fdm
write(fdm, password, strlen(password));
waitpid(-1, &status, 0);
close(fdm);
}
}
}
}


In that way isatty(STDIN_FILENO) in the target program returns 'true'.

isatty(STDIN_FILENO)

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