Capture transcript of program with redirected input and output

Question

A typical interaction for a program I've written might look like this:

Enter command: a_command
Completed a command

Enter command: another_command
Completed another command

I typically run my program like ./program < input.txt, where input.txt would contain:

a_command
another_command

I want to be able to capture the entire interaction (not just the output) like above. How can I do this with bash?

EDIT: program is a binary (specifically, it's in C++), not a bash script. I have access to the source code, but I'd like to do this without having to modify the source code.

Answer 1

In order to print the input after the corresponding prompt, you need to know when the program is waiting for input. There's no way to tell from observing the running program: you can't distinguish a program that's waiting for input on stdin from a program that's waiting for something else (network, disk, computation, …).

So the process to obtain a transcript which would look like interactive use has to go like this:

• Launch the program.
• Wait for — and recognize — the first prompt.
• Display and send the input to the first prompt.
• Ditto with the second prompt for input and all subsequent ones.
• Quit when the program exits.

The de facto standard tool to script this is Expect. The script would look something like this (warning: not working code, typed directly in my browser):

#!/usr/bin/expect -f
set transcript_file [open "transcript" wb]
spawn myprogram
expect "Enter command:"
puts -nonewline $transcript_file $expect_out(buffer)
send "a_command\r"
puts -nonewline $transcript_file "a_command\r"
puts -nonewline $transcript_file $expect_out(buffer)
send "another_command\r"
puts -nonewline $transcript_file "another_command\r"
puts -nonewline $transcript_file $expect_out(buffer)
…
expect eof
close $transcript_file

Answer 2

Add the line set -x in your program file.

Example:

#!/bin/bash
set -x #echo on

ls $PWD

This expands all variables and prints the full commands before output of the command.

output:

+ ls /home/user/
file1.txt file2.txt

Check this answer from Stackoverflow for more similar flags for the set command.