How to echo redirected stdin

Question

I execute an application from a script file and redirect stdin to it from here-doc like this:

my_cli << HERE_DOC
enable
configure
10
exit
exit
HERE_DOC

This works as expected, but I don't see neither the input nor the app output. The application is an interactive prompt written in C. When I interact manually with it, I see the prompt itself and responses to my input, but when I execute the aforementioned script I see nothing. I would like it to print the input and the output as if a real user was typing. Do you know how to achieve that?

Answer 1

It seems like there ought to be a better way, but you could use a wrapper function:

wrapper () { local text=$(</dev/stdin); echo "$text"; my_cli <<<"$text"; }
wrapper << HERE_DOC
enable
configure
10
exit
exit
HERE_DOC

To process the here doc line by line:

wrapper2 () { local line; while read -r line; do echo "$line"; my_cli <<<"$line"; done; }

If you manually interact with your program, does it show output? Does it output to stdout or stderr?

Another option that might work for you is expect.

Answer 2

I see Perl!

Well, you can't do it if you're using qx or system calls, since they are blocking in nature (yes, you can do system("program &") or call it from another thread and detach it.

Launcher thread:

threads->create( sub { 
                    threads->self->detach(); 
                    qx"$cmd > file1.cmd";
});

Main code: :

threads->create( sub {
while (1) { 
 get file size, if it is bigger than second ago - read new line, increase size
 parse new line, if any?
 sleep 1;
}
} );

Better, use POE::Wheel::FollowTail

Another solution is to redirect output of each of your programs to named fifo and read them all from your prog, keeping an eye for new lines.

man mkfifo

Answer 3

(tee /dev/fd/42 | mycmd) 42>&1 <<EOF
blah
blah
EOF

It won't look exactly like a real user - all input will be printed immediately. expect is probably better for this.