logging facility, rev.2

# place @ start of script for easy modification :)
# also, you're welcome to override
: ${LOG_LEVEL:=4} # read function log() @ <logging facility>
: ${LOG_FD:=2} # 1 = stdout, 2 = stderr

# ....

# <logging_facility>
clr_nc=$'\e[0m'
clr_red=$'\e[1;31m'
clr_green=$'\e[1;32m'
clr_yellow=$'\e[1;33m'
clr_cyan=$'\e[1;36m'
log() {
    local L=''
    [ $# -gt 0 ] && L=$1 && shift
    L=${L:-'U'} # 'U' means 'unclassified'

    local c0=${clr_nc} c1=''
    case "$L" in
    E) test ${LOG_LEVEL} -lt 1 && return 0; c1=${clr_red} ;;
    W) test ${LOG_LEVEL} -lt 2 && return 0; c1=${clr_yellow} ;;
    I) test ${LOG_LEVEL} -lt 3 && return 0; c1=${clr_green} ;;
    D) test ${LOG_LEVEL} -lt 4 && return 0; c1=${clr_cyan} ;;
    *) test ${LOG_LEVEL} -lt 4 && return 0; c1=${clr_nc} ;;
    esac
    [ ! -t ${LOG_FD} ] && c0='' && c1=''

    {
        [ $# -gt 0 ] \
        && echo "[${c1}$L${c0}] ${c1}$@${c0}" \
        || sed -re "s#^(.*)\$#[${c1}$L${c0}] ${c1}\\1${c0}#"
    } >&${LOG_FD}
}
# </logging_facility>