Script to add a page-level variable to content front matter in hugo

This was originally a question posed on the hugo discussion forums.

The user wanted to loop through all her content files and add a weight page-level variable to the front matter. The value of weight needed to be the first 2 characters of the content filename, since her content was named like 01_content.md, 02_content.md, etc.

She then wanted to range through her pages by their weight, like so:

{{ range .Pages.ByWeight }}
<!-- some code -->
{{ end }}

The script

#!/bin/bash

for file in *.md; do
    weight=${file:0:2}
    awk -v weight=$weight '/---/{
        count++
        if(count == 2){
        sub("---","weight: " weight "\n---",$0)
        }
    }
    {print}' $file > tmp && mv tmp $file
done

Explained

Loop through all files in the directory with extension .md:

for file in *.md; do
    # ...
done

Set a variable using the first 2 characters of the filename:

weight=${file:0:2}

Call an awk program and pass it a weight variable:

awk -v weight=$weight

When the awk program encounters the 2nd occurrence of --- (which is how you end front matter in YAML), it inserts the weight page-level variable on the line above:

'/---/{
    count++
    if(count == 2){
    sub("---","weight: " weight "\n---",$0)
    }
}
{print}'

Redirect the output of the awk program to a tmp file, then overwrite the original content file with the tmp file:

> tmp && mv tmp $file

Result

Original 01_content.md:

---
title: "Some title"
draft: false
---

Updated 01_content.md:

---
title: "Some title"
draft: false
weight: 01
---