Replaces variables in a template using shell script

gistfile1.sh

#!/bin/bash
if [ $# -eq 0 ]
then
  echo "Templater"
  echo "Copies templates from one folder to another."
  echo "Only replaces variables that exist in the environment"
  echo "Usage: templater IN_FOLDER OUT_FOLDER"
  exit 1
fi

if [ ! "$(ls -A $1)" ]; then
  # No files, nothing to do
  exit 0
fi

ENV_VARS=$(env | sed 's/=.*//')
#Fix ordering to make longer variable name get used first
ENV_VARS=$(echo "$ENV_VARS" | awk '{ print length, $0 }' | sort -n -r | cut -d" " -f2-)
FILES=$1/*
# Loop over files in folder
for f in $FILES; do
  # Grab text to variable
  text=$(<$f)
  # Loop over environment variables
  while read -r env_var; do
    val="${!env_var}"
    #escape value for sed
    val=$(echo "$val" | sed 's/[\/&]/\\&/g')
    string="\$$env_var"
    text=$(echo "$text" | sed "s/$string/$val/g")
  done <<< "$ENV_VARS"
  # Output files
  echo "$text" > "$2/$(basename $f)"
done