Executes a command, stores its output and prints the differences compared to the last execution (for log)

cmd_out_log.sh

#!/bin/bash 

last_out="$1"
shift
exec_cmd="$@"

script_date=$(date)
date_to_file=$(date '+%Y-%m-%d_%H.%M.%S')
base_dir=$(dirname ${last_out})
name_out=$(basename ${last_out})
file_suffix="/tmp/cmd_out_log_${name_out}"

if [[ ! -d "${base_dir}" ]] ; then
  mkdir -p "${base_dir}"
fi

if [ ! -e "${last_out}" ] ; then
  touch "${last_out}"
fi

out_file="${file_suffix}.out"
dif_file="${file_suffix}.dif"

rm ${out_file}.* 2> /dev/null
rm ${dif_file}.* 2> /dev/null

out_tmp=$(mktemp "${out_file}_${date_to_file}.XXXXXXXXX")
dif_tmp=$(mktemp "${dif_file}_${date_to_file}.XXXXXXXXX")

${exec_cmd} > ${out_tmp}

diff ${out_tmp} ${last_out} &> ${dif_tmp}

if (( $? == 0 )) ; then
  rm ${out_tmp}
else
  mv ${out_tmp} ${last_out}
  echo ${script_date}
  cat ${dif_tmp}
fi

rm ${dif_tmp}

Examples of use in crontab

* * * * * /opt/scripts/cmd_out_log.sh /etc/cmd_out/crontab-l /usr/bin/crontab -l >> /var/log/crontab-l.log 2>&1
* * * * * /opt/scripts/cmd_out_log.sh /etc/cmd_out/fdisk-l /sbin/fdisk -l >> /var/log/fdisk-l.log 2>&1
* * * * * /opt/scripts/cmd_out_log.sh /etc/cmd_out/blkid-olist /sbin/blkid -o list >> /var/log/blkid-olist.log 2>&1