TextFSM Tutorial

This repository provides a series of step-by-step examples illustrating how to parse text with the TextFSM library. Each step focuses on a specific feature or technique, allowing you to gradually become familiar with TextFSM's template syntax and parsing capabilities.

Overview

TextFSM is a Python library that facilitates parsing of semi-structured text data. It uses templates containing regular expressions to match and extract information. These templates can be especially helpful when parsing network device outputs, logs, or other text-based data formats that do not have consistent, tabular structures.

The tutorials in this repository showcase various ways to leverage TextFSM’s capabilities:

• Step 0: Introduction to TextFSM with a simple example of parsing first and last names.
• Step 1+: Progressively more complex use cases, such as handling multiple records, using states to separate sections, filling down values, requiring values, and other common text-parsing tasks.

Repository Structure

Below is a brief overview of the files and folders in the basics/ directory:

• step_0_introduction.py
  Demonstrates how to parse a simple string ("John Doe") to extract the first and last names.

• step_1_multiple_records.py
  Shows how to handle multiple lines of similar format.

• step_2_states_separator.py
  Introduces state management in TextFSM templates to handle varied text sections.

• step_3_value_filldown.py and step_3_0_value_filldown.py
  Illustrate how to fill down values when some fields are missing in subsequent lines.

• step_4_value_required.py
  Demonstrates the concept of required values in your parsed data.

• step_5_remove_the_clutter.py
  Shows strategies to clean up unwanted parts of the output and simplify templates.

• common.py
  Contains shared helper functions, including run_textfsm(), used by all examples to run the parsing logic.

Getting Started

1. Clone the Repository

   git clone https://github.com/Attumm/textfsm_tutorial
   cd textfsm_tutorial

2. Create and Activate a Virtual Environment

   python3 -m venv .venv
   source .venv/bin/activate    # Linux/Mac
   # or
   .venv\Scripts\activate       # Windows
   
   pip install -r requirements.txt

3. Install Dependencies
   Make sure TextFSM is installed:

   pip install textfsm

4. Run the Examples
   Navigate to the basics/ folder and run any of the step scripts. For instance, to run the first example:

   cd basics
   python step_0_introduction.py

Notes on Usage

• Each example is self-contained. Review the source code in each script for guidance on how TextFSM templates are defined and used.
• The run_textfsm() function in common.py encapsulates the typical loading and execution steps of TextFSM, so you do not have to write the boilerplate code repeatedly.