is there a way to redirect the input and output to the same file?

Question

I have a C++ program that outputs prompts and takes user input via the standard input stream cin.

I want to get a full transcript including both the program's output and the input in a file.

I know I can redirect input/output with command-line redirection (i.e. ./program < in.txt > out.txt), but this will only fill out.txt with the program's output in response to the input from in.txt.

I want to have a transcript that shows both the input and output. That is, let's say my program outputs a prompt "\nEnter a number: ", takes a user inputted number and outputs its double, "\nTwice your number is: ", and keeps doing this until the user enters a 0.

Let's say I have in.txt containing:

1
3
0

Then I want to have a transcript of input/output:

Enter a number: 1
Twice your number is: 2
Enter a number: 3
Twice your number is: 6
Enter a number: 0
Twice your number is: 0

Sorry if I didn't explain this very well... I didn't really know how to word it.

Is there a way to do this simply, or do I just have to enter the input by hand... and do some save of the terminal...

Answer 1

script doesn't cover your exact use case. You'd like to see the input and output to your program exactly as a user would see it, but without having to do it yourself.

I found Expect, which seems to be exactly what we're looking for. I don't know Tcl, but there's a Python port, pexpect. You'll need to install pexpect:

wget http://pexpect.sourceforge.net/pexpect-2.3.tar.gz
tar xzf pexpect-2.3.tar.gz
cd pexpect-2.3
sudo python ./setup.py install

Then copy this code into an executable file:

#! /usr/bin/env python

import sys, pexpect

executable = sys.argv[1]
infile = sys.argv[2]

proc = pexpect.spawn(executable)
file = open(infile)

for line in file:
    proc.send(line)

proc.sendeof()
proc.expect(pexpect.EOF)
print proc.before,

And then you can run it like so:

transcript ./executablefile fileforinput

My sample run gave me this output:

Enter a number: 1
Twice your number is: 2
Enter a number: 2
Twice your number is: 4
Enter a number: 3
Twice your number is: 6
Enter a number: 0
Twice your number is: 0

Assuming I read your question right, that should be the exact answer you're looking for. And it works on any program without any modification at all.

Hope that helps!

-Jake

Answer 2

The UNIX script command will do it.