Add custom last-updated-date pre-commit hook

Author: kencx

.pre-commit-config.yaml

@@ -9,3 +9,12 @@ repos:
       - id: check-toml
       - id: mixed-line-ending
       - id: check-merge-conflict
+  - repo: local
+    hooks:
+      - id: last-updated-date
+        name: last-updated-date
+        entry: bin/last-updated-date
+        language: system
+        types: ["markdown"]
+        files: ^content/
+        exclude: ^_index.md$

bin/last-updated-date

@@ -0,0 +1,53 @@
+#!/usr/bin/env bash
+
+# SOURCE: https://gist.github.com/welpo/6594765f5640982cb5886c9e9459ef5b
+# 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