replace.sh

#!/bin/bash

#
# replace.sh
#
# Replace template-like sequences in text files with the value of similarly named environment
# variables that the script knows about.
#
# For example, for a file named test.txt with the contents `{{HOME}} is where the {{THING}} is`,
# running `THING=heart replace.sh . test.txt` would transform the contents of the file into
# `/home/youruser is where the heart is`.
#
# The script always runs recursively from the given directory.
#
# Variables can be passed to the script right before execution or pre-defined in the
# environment.
#

#
# script usage info (when arguments are wrong or missing)
function usage() {
  echo "Usage: [environment] $0 <directory> <glob>" 1>&2
  echo "Example: VAR1=VAL1 VAR2=VAL2 $0 my-conf-directory '*.conf'" 1>&2
  exit -1
}

#
# find sequences like {{SOMETHING}} in files that match GLOBPATTERN in the given DIRECTORY
function get_variables() {
  for line in `grep -hroP --include=$GLOBPATTERN '{{(\S+)}}' $DIRECTORY | sort | uniq`
  do
  	if [[ $line =~ \{\{(.+)\}\} ]]
  	then
  		echo ${BASH_REMATCH[1]};
  	fi
  done
}

#
# $1: directory to recurse under
# $2: glob pattern to match files
#
DIRECTORY=$1
GLOBPATTERN=$2

#
# if either is not given, don't run
[[ -z $DIRECTORY ]] && usage
[[ -z $GLOBPATTERN ]] && usage

#
# perform replacements
for v in `get_variables`
do
  if [[ -n ${!v} ]]
  then
    echo "Replacing '{{$v}}' with ${!v}"
    find $DIRECTORY -type f -name $GLOBPATTERN -exec sed -i -e "s|{{$v}}|${!v}|g" {} \;
  fi
done