#!/bin/sh

# Check if URL is set
if [ -z "$URL" ]; then
  exit 1
fi

# Check if INTERVAL_TIME is set
if [ -z "$INTERVAL_TIME" ]; then
  INTERVAL_TIME=300
fi

# Infinite loop
while :
do
  curl $CURL_PARAM $URL
  sleep $INTERVAL_TIME
done

#!/bin/sh

# Check if URL is set
if [ -z "${URL}" ]; then
  exit 1
fi

# Check if INTERVAL_TIME is set
if [ -z "${INTERVAL_TIME}" ]; then
  INTERVAL_TIME=300
fi

# Infinite loop
while :
do
  curl ${CURL_PARAM} ${URL}
  sleep ${INTERVAL_TIME}
done

Use of {} brackets around variables
Use of {} brackets around variables
