taillog: tail FILE in --follow mode highlighting with colors the severity

taillog.sh

#!/usr/bin/env bash
#
# taillog: tail FILE highlighting with colors the severity.
#
#   Based in the script found at https://serverfault.com/a/1022806/256983
#
#   TODO: check whether the syntax "\<MESSAGE\>" offers better compatibility than "\bMESSAGE\b" to match whole words only (Mac OS)

if [ "$1" = "-h" -o "$1" = "--help" ]
then
    echo -e "\033[1;1mtaillog\033[0m: tail FILE in --follow mode highlighting with colors the severity: \033[1;36mdebug\033[0m, \033[1;32minfo\033[0m, \033[1;33mwarn\033[0m, \033[1;31merror\033[0m or \033[1;31mfatal\033[0m."
    echo
    echo -e  "\033[1;1mUsage: taillog [FILE]\033[0m"
    echo
    echo "If FILE is not provided, it tails the standard input."
    echo
    echo -e "If \033[1;1m\$GREP_ARGS\033[0m is set, it filters with grep the output with the given arguments and show the results in \033[1;35mpurple\033[0m."
    echo
    echo "E.g. to filter only logs from Postgres you might use:"
    echo
    echo "    $ GREP_ARGS=\"^postgres:\" taillog file.log"
    echo
    echo "The opposite filter to NOT get the logs from Postgres might be:"
    echo
    echo "    $ GREP_ARGS=\"-v ^postgres:\" taillog file.log"
    echo
    echo -e "You can also override the default arguments passed to tail (\`-f -n 100') with the env variable \033[1;1m\$TAIL_ARGS\033[0m."
    exit
fi

shopt -s expand_aliases

alias filter-grep="GREP_COLOR='1;35' grep -i -E --color=always --line-buffered"
alias grey-grep="GREP_COLOR='1;30' grep -i -E --color=always --line-buffered"
alias red-grep="GREP_COLOR='1;31' grep -i -E --color=always --line-buffered"
alias green-grep="GREP_COLOR='1;32' grep -i -E --color=always --line-buffered"
alias yellow-grep="GREP_COLOR='1;33' grep -i -E --color=always --line-buffered"
alias cyan-grep="GREP_COLOR='1;36' grep -i -E --color=always --line-buffered"

if [ -z "${TAIL_ARGS+x}" ]
then
    TAIL_ARGS="-f -n 100"
fi

if [ -z "$GREP_ARGS" ]
then
    tail $TAIL_ARGS $1 | cyan-grep "\bdebug\b|$" | green-grep "\binfo\b|$" | yellow-grep "\bwarn\b|\bwarning\b|$" | red-grep "\berror\b|\bfatal\b|\bcritical\b|\bCommandError\b|\bTimeoutError\b|\bexception\b|\bTraceback\b|$"
else
    tail $TAIL_ARGS $1 | filter-grep $GREP_ARGS | cyan-grep "\bdebug\b|$" | green-grep "\binfo\b|$" | yellow-grep "\bwarn\b|\bwarning\b|$" | red-grep "\berror\b|\bfatal\b|\bcritical\b|\bCommandError\b|\bTimeoutError\b|\bexception\b|\bTraceback\b|$"
fi