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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.