togglecpuperf.sh

#!/usr/bin/env bash
# Toggle CPU performance in a binary fashion.
# Alexandre Gauthier 2011-2012
#
# Done out of disgust at how the example shell script in one of these
# "language-du-jour is better than a shell script" talks.
#
# Requirements -->
#  Toggle the sysctl value of hw.setperf between '0' and '100'.
#  Talk implied little error checking was done in shell scripts, which
#   I feel is a matter of personal style over language suitability.
#
# NOTE: Since the 'off' value is '0' which is unixese for 'true' based on
#  return codes, I could abuse that, making it clever but horrible. So I don't.
#  It /would/ probably result in less code, but who gives a shit, I hate
#  using side effects, it's a terrible idea.
#

# Path to sysctl binary
SYSCTL=/bin/sysctl

# On/Off values
# Should these ever change.
ONVAL=100
OFFVAL=0

# Simple sanity check.
[[ ! -x $SYSCTL ]] && { echo "Unable to exec /bin/sysctl" 1>2 ; exit 1 ;}

# Current performance value
PERF=$(${SYSCTL} hw.setperf | cut -d '=' -f 2)

# setperf helper function
# sets hw.setperf to $0
setperf() {
	echo "hw.setperf: $PERF -> $0"
	sudo $SYSCTL -w hw.setperf=$0 || { echo "Failed to apply value." 1>2 ;}
}

# Validate that value is not suddendly unexpected
# TODO: Could very well be moved up here in the setperf() function.
if [[ $PERF -ne $ONVAL || $PERF -ne $OFFVAL ]] ; then
	echo "Got invalid value from sysctl ($PERF)." 1>2
	echo "Will only toggle between ${ONVAL} and ${OFFVAL}." 1>2
	exit 1
fi

# Toggle sysctl value.
[[ $PERF -eq $ONVAL ]] && setperf $OFFVAL || setperf $ONVAL
exit 0