Shell Programming and Scripting

Suppose I have a program that I've written that accepts input, ie this C++ program:

Code:

#include <iostream>

using namespace std;

int main()
{
    cout << "Enter something:" << endl;
    int x;
    cin >> x;
    cout << "You entered data" << endl;
}

Suppose that I have a text file, in.txt containing this:
1

Now I run my program on the command line (supposing I named it input.exe

Code:

input.exe < in.txt

If I do this, I see the "Enter something" and the "You entered", but I will not see the entered 1 show up where the cin took place.

How do I get the 1 to print in between them (without modifying the C++ program)? I know that some tools such as expect will do this, but I've found expect to be a pain to get it to not pause when it doesn't match a regular expression. Printing input to programs would be really useful while grading C++ programs for students when testing with a lot of inputs.

Here's my Linux version:

Code:

% cat /etc/*-release
Red Hat Enterprise Linux Workstation release 6.3 (Santiago)
Red Hat Enterprise Linux Workstation release 6.3 (Santiago)

I'm currently using this shell:

Code:

% echo $SHELL
/bin/tcsh

Well, you can 'tee -a |' what is flowing into stdin to /dev/tty or the log, but it will not be in sync, as stdin as a buffered FILE* that often reads ahead, especially if stdin is not tied to a terminal but a pipe. Modifying the C++ is the only way, and if it is worth saying that you are asking and that you got something, then it is worth saying what you got.

Code:

cout << "You entered data '" << x << "'." << endl;

In the world of debug tools, you can strace/truss/tusc the shell running this and all its children and see what is going on, as it shows all system calls and on some systems (Solaris truss -u'*' ) can also show library calls.

Modifying C++ files is not effective, because there are 45 of them per assignment, and the goal is to save time by generating a "report" of people's output. The tee may be the best solution as it would show the input directly above the output (with input stripped out there).

I was trying to get them to show together using expect, as below.
However, when a regular expression does not match, it pauses and waits for me to manually type the desired input. This doesn't work well if I set it loose on a large batch of files to grade.

Where should I post this tcl/expect problem so that someone knowledgeable might see it? a.out is the executable.

#!/usr/bin/expect
set one [lindex $argv 0]
set two [lindex $argv 1]
set three [lindex $argv 2]
set four [lindex $argv 3]

spawn "./a.out"

expect -nocase -regexp "(.*Enter.*|.*Input.*)" { send -- "$one\r" }
expect -nocase -regexp "(.*)" { send -- "$two\r" }
expect -nocase -regexp "(.*Enter.*|.*Input.*)" { send -- "$three\r" }
expect -nocase -regexp "(.*)" { send -- "$four\r" }

interact

If you run under script, you have a full transcript: Man Page for script (opensolaris Section 1) - The UNIX and Linux Forums

I gave it a quick try, but it did not show the input alongside the output, since this command will only record what showed up on my console window, which does not display input within output.

% script -a script.txt
Script started, file is script.txt

% a.out < in.txt
Enter something:
You entered data

% exit

exit
Script done, file is script.txt

$ cat script.txt
Script started on Fri 15 Feb 2013 04:13:39 PM EST

% a.out < in.txt/script
Enter something:
You entered data

%

exit

Script done on Fri 15 Feb 2013 04:13:47 PM EST
Script started on Fri 15 Feb 2013 04:14:48 PM EST

%
Enter something:
You entered data

%

exit

You must have the stty set to no echo in full duplex or raw. Did the C++ do that?

Command autoexpect records everything in and out into an expect script, so you can do it all over again unless there are time artifacts. It creates an intermediate pseudo tty.