bisect

#!/bin/bash
# print the first version where script exits non-zero

usage() {
    cat <<EOF 1>&2
Usage: $scriptname <script> <good> <bad>
EOF
}

error() {
    echo "$scriptname: $*" >&2
}

scriptname=bisect

while getopts ":h" option; do
    case $option in
    h)
        usage
        exit 0
        ;;
    ':')
        echo "Missing argument to -$OPTARG" 1>&2
        usage
        exit 2
        ;;
    '?')
        echo "Invalid option -$OPTARG" 1>&2
        usage
        exit 2
        ;;
    *)
        echo "Program does not support -$option yet" 1>&2
        usage
        exit 2
        ;;
    esac
done
shift $((OPTIND - 1))

script=$1
good=$2
bad=$3

if [[ -z $script ]] || [[ -z $good ]] || [[ -z $bad ]]; then
    usage
    exit 2
fi
if ! [[ -x $script ]]; then
    error "$script is not executable"
    exit 1
fi
if ((bad <= good)); then
    error "bad version must be higher than good version"
    exit 1
fi

logfile="$HOME/bisect.$(date +%Y%m%d.%H%M%S)"
log() {
    echo "$(date) $*" >> "$logfile"
    echo "$*" >&2
}

log "Given $good is good and $bad is bad..."
while ((bad-good > 1)); do
    version=$((good + (bad-good)/2))
    echo "Testing $script at $version..." >> "$logfile"
    echo "==========" >> "$logfile"
    if "$script" "$version" >>"$logfile" 2>&1; then
        log "$version is good"
        good=$version
    else
        log "$version is bad"
        bad=$version
    fi
    echo "==========" >> "$logfile"
done

log "$bad is bad"