How to substitute values in a key-value file if keys exists in shell environment?

>>> from string import Template
>>> s = Template('$who likes $what')
>>> s.substitute(who='tim', what='kung pao')
'tim likes kung pao'

configfile=./Configuration.conf

. "$configfile"

declare -A configlist

while IFS='=' read -r key val ; do

  # skip empty / commented lines and obviously invalid input
  [[ $key =~ ^[[:space:]]*[_[:alpha:]] ]] || continue

  # Stripping up to the last space in $key removes "export".
  # Using eval to approximate the shell's handling of lines like this:
  #    var="some thing with spaces" # and a trailing comment.
  eval "configlist[${key##* }]=$val"

done < "$configfile"

# The keys are "${!configlist[@]}", the values are "${configlist[@]}"
#
#for key in "${!configlist[@]}" ; do
#  printf '"%s" = "%s"\n' "$key" "${configlist[$key]}"
#done

for value in "${configlist[@]}" ; do
  : your logic goes here
done

awk -F',' 'NR==FNR{k[$1]=$2;next}
         {for(x in k)gsub(x,k[x]);print}' lookup.file targetfile

A,foo
foo,bar
bar,blah

a.*, B
b-$, foo

xxx=xxxxx
yyy=yyyyy
zzz=zzzzz

#!/bin/ksh
while read line.
do
  user=${line%%=*}
  ip=${line##*=}
  # example how to access the values
  printf "user: %s  IP: %s\n" "${user}" "${ip}"
done < your.properties

user: xxx  ip: xxxxx
user: yyy  ip: yyyyy
user: zzz  ip: zzzzz

user=www
ip=wwwww
user=xxx
ip=xxxxx
user=yyy
ip=yyyyy
user=zzz
ip=zzzzz

#!/bin/sh
# the file input from file `your.properties` is redirected to filedescriptor 3
# to avoid problems with programs inside the loop which themself use `stdin`
# for reading input
while read user <&3; read ip <&3
do
  user=${user##*=}
  ip=${ip##*=}
  # example how to access the values
  printf "user: %s  ip: %s\n" "${user}" "${ip}"
done 3< your.properties

user: www  ip: wwwww
user: xxx  ip: xxxxx
user: yyy  ip: yyyyy
user: zzz  ip: zzzzz

# grab the output file name
file=$1
shift
# loop through the rest of args which are names of variables that
# need to be substituted
for var in "${@}"; do
  # note: ${var} and ${!var} do get evaluated inside single quotes so long as 
  # there are enclosing double quotes around them
  sed_expr=${sed_expr}" -e 's/\${$var}/${!var}/'"
done

# enclose sed_expr as well file in double quotes to prevent
# word splitting and globbig
sed -i "$sed_expr" "$file"

export ID="toto" SECRET="tata" OTHER="franck"
./config.sh file ID SECRET OTHER

ID="toto" SECRET="tata" OTHER="franck" ./config.sh file ID SECRET OTHER

-e 's/${ID}/toto/' -e 's/${SECRET}/tata/' -e 's/${OTHER}/franck/'

$clientId = 'toto';
$clientSecret = 'tata';
$publication = 'franck';