Use gifsicle to resize GIFs for Slack emoji

smallify.sh

#!/usr/bin/env bash

set -eo pipefail

srcdir="$1"
if [ -z "$srcdir" ]; then
  echo "usage: $0 <dir>"
  exit 1
fi

destdir="$srcdir-slack"
mkdir -p "$destdir"

MAXSIZE=128000

sizeof() {
  wc -c "$1" | perl -lane'print $F[0]'
}

numframes() {
  gifsicle "$1" -I | grep -E "\d+ images" --only-matching | grep "[0-9][0-9]*" --only-matching
}

delayof() {
  local x=$(gifsicle "$1" -I | grep -E 'delay \d+(?:\.\d+)' --only-matching | grep -E '\d.*' --only-matching | tail -n 1)
  echo "$x * 100" | bc | grep -E '\d+' --only-matching | head -n 1
}

g="gifsicle -O3 --colors=256"

for src in "$srcdir"/*.gif; do
  dest="$destdir/$(basename "$src")"

  n="$(numframes "$src" || echo 0)"
  d="$(delayof "$src" || echo 0)"

  declare -a cmds=(
    '$g --resize=128x128 \"$src\" -o \"$dest\"'
    '$g --resize=96x96 \"$src\" -o \"$dest\"'
    '$g --resize=64x64 \"$src\" -o \"$dest\"'

    '$g --resize=128x128 --lossy=30 \"$src\" -o \"$dest\"'
    '$g --resize=96x96 --lossy=30 \"$src\" -o \"$dest\"'
    '$g --resize=64x64 --lossy=30 \"$src\" -o \"$dest\"'

    '$g --resize=128x128 --lossy=80 \"$src\" -o \"$dest\"'
    '$g --resize=96x96 --lossy=80 \"$src\" -o \"$dest\"'
    '$g --resize=64x64 --lossy=80 \"$src\" -o \"$dest\"'

    '$g --resize=128x128 \"$src\" -d $((d*2)) $(seq -f \"#%g\" 0 2 $(($n - 1))) -o \"$dest\" -o \"$dest\"'
    '$g --resize=96x96 \"$src\" -d $((d*3)) $(seq -f \"#%g\" 0 3 $(($n - 1))) -o \"$dest\" -o \"$dest\"'
    '$g --resize=64x64 \"$src\" -d $((d*3)) $(seq -f \"#%g\" 0 3 $(($n - 1))) -o \"$dest\" -o \"$dest\"'

    '$g --resize=128x128 \"$src\" -d $((d*3)) $(seq -f \"#%g\" 0 3 $(($n - 1))) -o \"$dest\" -o \"$dest\"'
    '$g --resize=96x96 \"$src\" -d $((d*3)) $(seq -f \"#%g\" 0 3 $(($n - 1))) -o \"$dest\" -o \"$dest\"'
    '$g --resize=64x64 \"$src\" -d $((d*3)) $(seq -f \"#%g\" 0 3 $(($n - 1))) -o \"$dest\" -o \"$dest\"'
  )

  echo "$src"
  for cmd in "${cmds[@]}"; do
    rm -f "$dest"
    echo "> $cmd"
    eval eval $cmd
    if [ $(sizeof "$dest") -le "$MAXSIZE" ]; then
      break
    fi
  done

  echo -n "Final size: $(sizeof "$dest")"
  if [ $(sizeof "$dest") -gt "$MAXSIZE" ]; then
    echo "********** STILL TOO BIG **********"
  fi

  echo
  echo
done

Bulk deletion snipped in case you make a mistake: https://gist.github.com/nealey/5549ec14a182bc59510dd76f62e2bc64