autoexpect

Spawn a shell and generate a script from it

$ autoexpect

$ autoexpect [command]

$ autoexpect -f [path/to/file] [command]

autoexpect [options] [command [args ...]]

-f scriptfile
    Specifies the name of the output Expect script file. Default is script.exp.

-P prefix
    Sets a prefix for temporary files used by autoexpect.

-C chardelay
    Adds a delay (in milliseconds) after each character sent by the generated script during playback. Useful for slow systems or applications.

-T timeout
    Sets the default timeout (in seconds) for expect commands within the generated script.

-D debugfile
    Records debugging information from the generated Expect script to the specified file.

-l logfile
    Logs the entire terminal session (input and output) to the specified file, in addition to generating the script.

-r
    Forces autoexpect to use raw mode, preventing interpretation of special characters like backspaces or control sequences.

-t
    Includes timestamps for events in the generated script, which can be useful for analysis.

-s
    Causes autoexpect to output the 'send' commands when creating the script.

-a
    Appends the generated Expect script to the specified output file instead of overwriting it.

command [args ...]
    The command and its arguments to execute and record during the session. If omitted, autoexpect starts a shell.

autoexpect is a utility that automates the creation of Expect scripts by observing an interactive session. When launched, it records all user input and program output within a terminal. Upon completion of the session, autoexpect translates this recorded interaction into a runnable Expect script.

This generated script can then be used to automatically replay the exact sequence of commands and responses, effectively automating tasks that require human interaction, such as logging into remote servers, installing software, or running interactive diagnostic tools. It significantly simplifies the process of writing complex Expect scripts manually, reducing potential errors and saving considerable development time for repetitive or testing scenarios. While providing a robust starting point, the resulting script often requires manual refinement for increased robustness and flexibility.

Autoexpect generates scripts based on exact observed interactions, making them potentially 'fragile.' Minor changes in the interactive program's output (e.g., slight variations in prompts, timing differences, or new lines) can break the generated script.

For robust automation, the generated script almost always requires manual editing to generalize patterns, handle variable input, incorporate error checking, and manage sensitive information like passwords more securely. It may also include redundant or overly specific expect patterns that need simplification.

Autoexpect operates by creating a pseudo-terminal (pty) and inserting itself between the user's terminal and the program being run. It monitors all data passing through this pty, capturing everything typed by the user and everything output by the program. Based on this observation, it constructs an Expect script using expect commands to wait for specific output patterns and send commands to reproduce the user's input. The generated script effectively mimics the recorded interactive session.

While autoexpect provides a great starting point, always review and refine the generated script. Replace hardcoded strings with regular expressions where appropriate (e.g., `expect -re "(yes/no)"`). Use variables for sensitive data like passwords instead of embedding them directly. Add comments to explain complex logic. Test the script thoroughly in various scenarios to ensure its robustness against minor environmental changes or unexpected program outputs.

The Expect tool, which autoexpect is a part of, was developed by Don Libes at the National Institute of Standards and Technology (NIST) in the early 1990s.

Autoexpect itself emerged as a powerful utility accompanying the Expect package, designed to lower the barrier to entry for users wanting to automate interactive processes without deep knowledge of the Expect syntax. Its development reflects the need for simpler script generation in complex automation environments, leveraging Expect's capabilities to observe and record real-time terminal interactions.

expect(1), script(1), tcl(1)