Move the date-last-month-year to a function.

.bauke/Restic Backups.md

@@ -44,7 +44,7 @@ restic-b2 check
 * Monthly music library backup:
 
 ```zsh
-restic-b2 backup --tag "$(date -d "$(date +'%Y-%m-01') -1 day" +'%B %Y')" ~/Beets
+restic-b2 backup --tag "$(date-last-month-year)" ~/Beets
 ```
 
 * KeePassXC database:

.functions.zsh

@@ -1,3 +1,12 @@
+# Returns the previous month as "Month Year" (ie. "April 2023").
+# date-last-month-year
+date-last-month-year () {
+  # The inner date "+'%Y-%m-01'" gets the date of the current month with 01 as the day.
+  # Then that date has 1 day subtracted (date -d ... -1 day).
+  # And finally "+'%B %Y'" gets the resulting date as the month and year.
+  date -d "$(date +'%Y-%m-01') -1 day" +'%B %Y'
+}
+
 # Copies a section from a video using ffmpeg.
 # extract-clip <input file> <start timestamp> <end timestamp> <output file>
 extract-clip () {