git pre-commit script to update the date of Zola's posts

pre-commit

#!/usr/bin/env bash
# Requires Bash 4.0 or newer.

# This script updates the 'updated' field in the front matter of modified .md
# files setting it to their last modified date.

# Function to exit the script with an error message.
function error_exit() {
    echo "ERROR: $1" >&2
    exit "${2:-1}"
}

# Function to extract the date from the front matter.
function extract_date() {
    local file="$1"
    local field="$2"
    grep -m 1 "^$field =" "$file" | sed -e "s/$field = //" -e 's/ *$//'
}

# Get the modified .md files, ignoring "_index.md" files.
mapfile -t modified_md_files < <(git diff --cached --name-only --diff-filter=M | grep -Ei '\.md$' | grep -v '_index.md$')

# Loop through each modified .md file.
for file in "${modified_md_files[@]}"; do
    # Get the last modified date from the filesystem.
    last_modified_date=$(date -r "$file" +'%Y-%m-%d')

    # Extract the "date" field from the front matter.
    date_value=$(extract_date "$file" "date")

    # Skip the file if the last modified date is the same as the "date" field.
    if [[ "$last_modified_date" == "$date_value" ]]; then
        continue
    fi

    # Update the "updated" field with the last modified date.
    # If the "updated" field doesn't exist, create it below the "date" field.
    awk -v date_line="$last_modified_date" '
    BEGIN {FS=OFS=" = "; first = 1}
    {
        if (/^date =/ && first) {
            print
            getline
            if (!/^updated =/) print "updated" OFS date_line
            first=0
        }
        if (/^updated =/ && !first) gsub(/[^ ]*$/, date_line, $2)
        print
    }' "$file" > "${file}.tmp" && mv "${file}.tmp" "$file" || error_exit "Failed to update file $file"

    # Stage the changes.
    git add "$file"
done

For more context, see my blog post: Zola Git Pre-Commit Hook: Updating Post Dates.

This is a Git pre-commit script that updates the 'updated' field in the front matter of modified .md files to the last modified date. This script can be used with static site generators like Zola to keep your front matter up to date.

Whenever you commit markdown files in your Git repository (e.g. your Zola site), the script will automatically update any modified .md files to include the last modified date in the front matter 'updated' field.

To use the script, copy and paste it into the .git/hooks/pre-commit file in your project's root directory. If the file doesn't exist, create it and make sure it's executable by running chmod +x .git/hooks/pre-commit.

For a version that also does PNG compression, check out this gist.