Bash script to convert mov screen recordings to gifs

mov2gif.sh

#!/bin/sh

if [ -z $1 ]
  then
  echo 'Usage: mov2gif [50%] [15fps] source_file [destination_file]'
  exit 1
fi

scale=1
scale_pat='^[0-9]+%$'
if [[ $1 =~ $scale_pat ]]
then
  scale=`echo $1 | tr -d % | sed -E 's/$/\/100/' | bc -l`
  set -- ${@:2:4}
fi

fps=30
fps_pat='^[0-9]+fps$'
if [[ $1 =~ $fps_pat ]]
then
  fps=`echo $1 | tr -d 'fps'`
  set -- ${@:2:3}
fi

source=$1
source_gif=`echo $source | sed -E 's/\..{1,4}$|$/.gif/'`
dest=${2:-$source_gif}

palette="/tmp/palette.png"
filters="fps=$fps,scale=iw*$scale:ih*$scale:flags=lanczos"

ffmpeg -v warning -i "$source" -vf "$filters,palettegen" -y "$palette"
ffmpeg -v warning -i "$source" -i "$palette" -lavfi "$filters [x]; [x][1:v] paletteuse" -y "$dest"

echo "wrote $dest at ${fps}fps, scale of $scale"