A Bash script that prints the current state of the CPU on a Raspberry Pi. It displays variables like temperature, voltage and speed.

cpustatus.sh

#!/bin/bash
# cpustatus
#
# Prints the current state of the CPU like temperature, voltage and speed.
# The temperature is reported in degrees Celsius (C) while
# the CPU speed is calculated in megahertz (MHz).

function convert_to_MHz {
    let value=$1/1000
    echo "$value"
}

function calculate_overvolts {
    # We can safely ignore the integer
    # part of the decimal argument
    # since it's not realistic to run the Pi
    # at voltages higher than 1.99 V
    let overvolts=${1#*.}-20
    echo "$overvolts"
}

temp=$(vcgencmd measure_temp)
temp=${temp:5:4}

volts=$(vcgencmd measure_volts)
volts=${volts:5:4}

if [ $volts != "1.20" ]; then
    overvolts=$(calculate_overvolts $volts)
fi

minFreq=$(cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_min_freq)
minFreq=$(convert_to_MHz $minFreq)

maxFreq=$(cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq)
maxFreq=$(convert_to_MHz $maxFreq)

freq=$(cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_cur_freq)
freq=$(convert_to_MHz $freq)

governor=$(cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor)

echo "Temperature:   $temp C"
echo -n "Voltage:       $volts V"
[ $overvolts ] && echo " (+0.$overvolts overvolt)" || echo -e "\r"
echo "Min speed:     $minFreq MHz"
echo "Max speed:     $maxFreq MHz"
echo "Current speed: $freq MHz"
echo "Governor:      $governor"

exit 0

On a raspberry pi2 I have this error executing this script:
cpustatus.sh: 23: cpustatus.sh: Bad substitution

/sys/devices/system/cpu/cpu0/cpufreq/scaling_cur_freq is wrong unfortunately! Don't trust in it if you're interested in CPU clock. This is controlled by the 'firmware', the kernel has no clue at which frequency the CPU cores are running and you need to query the firmware with vcgencmd measure_clock arm instead especially if you're interested in overclocking.

bamarni/pi64#4 (comment)