pdfcrop

#!/usr/bin/env zsh

IN_FILE="$1"
OUT_FILE="${IN_FILE%.pdf}_cropped.pdf"
PADDING_X=10
PADDING_Y=10

# Determine bounding box
MINMAX_AWK='{
if (NR==1) {left = $1; bottom = $2; right=$3; top=$4;}
else {
if ($1 < left) left = $1;
if ($2 < bottom) bottom = $2;
if ($3 > right) right = $3;
if ($4 > top) top = $4;
}}
END {print left, bottom, right, top}'
BBOX=(`gs -q -dBATCH -dNOPAUSE -sDEVICE=bbox "$IN_FILE" 2>&1 | grep -v HiResBoundingBox | sed 's/.*: *//' | awk "$MINMAX_AWK"`)
# BBOX=(left bottom right top)

echo "BBOX: $BBOX"

# Compute offset and new size
OFFSET_X=`expr $BBOX[1] - $PADDING_X`
OFFSET_Y=`expr $BBOX[2] - $PADDING_Y`
NEW_WIDTH=`expr $BBOX[3] - $OFFSET_X + $PADDING_X`
NEW_HEIGHT=`expr $BBOX[4] - $OFFSET_Y + $PADDING_Y`

echo "Offset: $OFFSET_X $OFFSET_Y"
echo "New size: $NEW_WIDTH $NEW_HEIGHT"

# Translate parameters for `pdfwrite`
OFFSET_X=`expr 0 - $OFFSET_X`
OFFSET_Y=`expr 0 - $OFFSET_Y`
NEW_WIDTH=`expr $NEW_WIDTH \* 10`
NEW_HEIGHT=`expr $NEW_HEIGHT \* 10`

# Crop PDF
gs \
  -o "$OUT_FILE" \
  -sDEVICE=pdfwrite \
  -g"$NEW_WIDTH"x"$NEW_HEIGHT" \
  -c "<</PageOffset [$OFFSET_X $OFFSET_Y]>> setpagedevice" \
  -f "$IN_FILE"

echo "Output written to '$OUT_FILE'."