Shell script to display a random message once per day

motd

#!/bin/bash

CONFIG_DIR=~/.config/motd
MESSAGES="${CONFIG_DIR}/messages"
MESSAGES_LAST_DISPLAY="${MESSAGES}-last-display"

if [ ! -f "$MESSAGES" ]; then
  echo "$0: Store messages in '${MESSAGES}' (file does not exist)"
  exit 1
fi

if [ ! -s "$MESSAGES" ]; then
  echo "$0: Cannot find any messages in '${MESSAGES}'"
  exit 1
fi

if [ ! -r "$MESSAGES" ]; then
  echo "$0: Cannot read messages from '${MESSAGES}' (file is not readable)"
  exit 1
fi

if [ -f "$MESSAGES_LAST_DISPLAY" ]; then
  TODAY=$(date +%F)
  LAST_DATE_DISPLAYED=$(date -r "$MESSAGES_LAST_DISPLAY" +%F)
  if [ "$TODAY" == "$LAST_DATE_DISPLAYED" ]; then
    # We already displayed a message today
    # (One motivational message a day is enough)
    exit 0
  fi
fi

# Get a random message from the file:
MESSAGE=$(shuf -n 1 "$MESSAGES" 2> /dev/null)

if [ -z "$MESSAGE" ]; then
  echo "$0: Empty message (blank line) found in '${MESSAGES}'"
  exit 1
fi

# Using \033 instead of \e for escape codes as \e wasn't working in iTerm on macOS
echo -e "\033[38;5;81m${MESSAGE}\033[m"

# Create file or update its last-modified-time (mtime):
touch "$MESSAGES_LAST_DISPLAY" &> /dev/null