Screen Record a Region to GIF with byzanz. Run, select rectangle, wait for beep and it will capture for 10sec then beep and save.

byzanz-record-region.sh

#!/bin/bash

# Directory to output the videos
DESTDIR=~/Videos/

# Delay before starting
DELAY=10

# Sound notification to let one know when recording is about to start (and ends)
beep() {
	paplay /usr/share/sounds/freedesktop/stereo/message-new-instant.oga &
}

# Duration and output file
if [ $# -gt 0 ]; then
	D="--duration=$@"
else
	FILENAME="${DESTDIR}recorded-$RANDOM.gif"
	echo Default recording duration 10s to ${FILENAME}
	D="--duration=10 ${FILENAME}"
fi

# xrectsel from https://github.com/lolilolicon/xrectsel
ARGUMENTS=$(xrectsel "--x=%x --y=%y --width=%w --height=%h") || exit -1

echo Delaying $DELAY seconds. After that, byzanz will start
for (( i=$DELAY; i>0; --i )) ; do
	echo $i
	sleep 1
done
beep
byzanz-record --verbose --delay=0 ${ARGUMENTS} $D
beep