MacOS WiFi signal-strength meter

signalMeter.sh

#!/bin/bash
#
# Authored by: Marceli Wac
#
# MacOS utility used for displaying the signal strength in a form of cascading progress bar
# prepended with a percentage value. Signal strength is expressed using cubic formula for
# conversion between dBm and % as described in http://cecas.clemson.edu/linux/nm-ipw2200.shtml
# Progress bar should be used for indication only.
# Uncertainty   progress bar:       +/- 2%
#               percentage value:   +/- 1%

clear
LOWER_WIFI_BAND=-92
UPPER_WIFI_BAND=-21
SIGNAL_PERCENTAGE=0
while x=1
  do
    SIGNAL=`/System/Library/PrivateFrameworks/Apple*.framework/Versions/Current/Resources/airport -I \
    | grep CtlRSSI \
    | sed -e 's/^.*://g'`
    if [[ "$SIGNAL" -lt "$LOWER_WIFI_BAND" ]]; then
        SIGNAL_PERCENTAGE=0
    else
        if [[ "$SIGNAL" -gt "$UPPER_WIFI_BAND" ]]; then
            SIGNAL_PERCENTAGE=100
        else
            SIGNAL_PERCENTAGE=$(( ((-154*SIGNAL*SIGNAL)-(3794*SIGNAL)+981820) / 10000 ))
        fi
    fi
    printf "%d%s " $SIGNAL_PERCENTAGE "%"
    for i in {0..50}
        do
            if [[ "$i" -lt $(($SIGNAL_PERCENTAGE/2)) ]]; then
                printf "O"
            else
                printf "-"
            fi
        done
    printf "\n"
    sleep 0.5
done