Executing string sent from one terminal in another in Linux pseudo-terminal

Question

Lets say I have one terminal where the output of "tty" is "/dev/pts/2" From another terminal, I want to send a command to the first terminal and execute it. Using: echo "ls" > "/dev/pts/2" only prints "ls" in the first terminal Is there a way to execute the string?

I don't think so, because that would be a huge security hole. — Basile Starynkevitch, Dec 30 '11 at 08:36

score 2 · Accepted Answer · answered Dec 30 '11 at 08:40

2

No; terminals don't execute commands. They're just channels for data.

You can sort of run a command and attach it to another terminal like this, though:

ls </dev/pts/2 >/dev/pts/2 2>/dev/pts/2

It won't behave exactly like you ran it from that terminal, though, as it won't have that device set as its controlling terminal. It's reasonably close, though.

answered Dec 30 '11 at 08:40

Yes, the thing executing commands is the shell, not the terminal. – Basile Starynkevitch Dec 30 '11 at 08:43
Thanks! didn't about just attaching the output to the terminal. It really helps. – Ameet Gohil Dec 30 '11 at 08:50

score 1 · Answer 2 · edited Jan 01 '13 at 20:34

1

I realize it's a year late, but there is a simpler way I think. Doesn't this work?

ls > /dev/pts/2

It works on my system.

edited Jan 01 '13 at 20:34

Sergiu Dumitriu

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answered Jan 01 '13 at 20:15

Joseph Spenner

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This works for `ls`, because it doesn't accept input and usually doesn't display error messages. It won't work for more complex commands, though. – Oct 29 '14 at 18:49

score 0 · Answer 3 · answered Jul 21 '21 at 16:37

You could execute /bin/sh > /dev/pts/5 to get a shell in the pty, then execute other commands. If you want a true shell functionality, you could maybe implement a thread (in a C program, with the openpty commands and all) to read the master pty and output its contents.

score 0 · Answer 4 · answered Dec 30 '11 at 08:40

0

Try

echo `ls`

notice different quote sign.

answered Dec 30 '11 at 08:40

vadchen

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those are back-tick not quotes – Alex Jones Feb 11 '16 at 15:27

score 0 · Answer 5 · answered Dec 30 '11 at 10:31

Usually getty, login, and shell programs are needed for executing commands from tty.

But you can also put a shell directly executing commands from a pseudo terminal. This is simplified example (all error checkings removed):

int main( int argc, char** argv )
{
    int master_fd = create_my_own_psudo_terminal() ;

    // Wait until someone open the tty
    fd_set fd_rset;
    FD_ZERO( &fd_rset );
    FD_SET( master_fd, &fd_rset );
    select( master_fd + 1, &fd_rset, NULL, NULL, NULL );

    dup2( master_fd, STDIN_FILENO );
    execl("/bin/sh", "sh", 0 );

    return 0;
}

Now you can do the following:

Start this simple program in the first terminal.

And send your command from the second terminal:

echo "ls" > /dev/pts/5

And you will get listing in the first terminal.

Note: This is quite unsecure, because login is not done.

Executing string sent from one terminal in another in Linux pseudo-terminal

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