glm-nml-edit

GLM Namelist Editor

Overview

The General Lake Model (GLM) uses Fortran namelist (.nml) files for configuration. This skill covers how to parse and update specific parameters in these files.

Setup

No special installation is required if using standard CLI tools like sed or python for string replacement. For more robust parsing, use a regex-based approach.

Usage Pattern: Python (Regex)

import re

def update_nml(file_path, section, parameter, value):
    with open(file_path, 'r') as f:
        content = f.read()

    # Find the section and update the parameter within it
    pattern = rf"(&{section}.*?\b{parameter}\s*=\s*)[^,\n]*"
    replacement = rf"\g<1>{value}"
    
    # Use flags=re.DOTALL to match across lines if needed, 
    # but GLM parameters are usually on one line.
    new_content = re.sub(pattern, replacement, content, flags=re.IGNORECASE | re.DOTALL)
    
    with open(file_path, 'w') as f:
        f.write(new_content)

Example: Bash (sed)

# Update Kw in &light section
sed -i '/&light/,/\// s/Kw *= *[0-9.]*/Kw = 0.45/' glm3.nml

Considerations

• GLM parameters are case-insensitive but usually lowercase.
• Parameters are grouped into blocks (e.g., &glm_setup, &light).
• Some parameters are arrays (e.g., the_depths = 0.0, 1.0, 2.0). Update these carefully to maintain format.
• Always verify the change with grep after modification.