A simple shell script used for converting pixel units to relative ems. It assumes a baseline of 16px if one isn't provided.

px2em

#!/bin/bash

baseline=16  # px
em=0
px=0
float_scale=3	# floating point precision for bc

function px2em()
{
  local result=$(echo "scale=$float_scale; $px / $baseline" | bc -q 2>/dev/null)
  result=$(printf '%*.*f' 0 "$float_scale" "$result")
  echo $result
}

# we need at least one argument
if [ $# -lt 1 ]
then
	echo "Usage: `basename $0` [baseline] pixel-value"
	exit 85
fi

if [ $# -eq 2 ]
then
	baseline=$1
	px=$2
else
  px=$1
fi

px2em

exit 0