python - How can I process variable substitutions in bash? -

so have files contain placeholder values @user@ or @shell@ (all-caps variable names, enclosed in @'s, representing environment variable names). want replace placeholders actual values of environment varables reference.

in past when i've seen sort of thing done, specific variables hard-coded, eg:

sed -e 's/@some_variable@/$some_value/' <infile >outfile 

but won't work current use-case want more flexibly support arbitrary substitutions. wrote code in python want:

import re import fileinput  os import environ sys import stdout  pat = re.compile(r'@([a-z_]+)@')  line in fileinput.input():     stdout.write(pat.sub(lambda match: environ[match.group(1)], line)) 

but i'd prefer not use python if can it. surely there's way perl or sed one-liner?

perl -pe 's/\@(\w+)\@/$env{$1}/g' 1 way job.

if want throw error if variable mentioned in file doesn't exist in environment, use

perl -pe 's/\@(\w+)\@/die "$1 not found\n" unless exists $env{$1}; $env{$1}/eg'