[SOLVED] Extract environment variables from actual usage in nodejs projects and generate a .env.sample file

Issue

The .env.sample files in the projects i work with are always outdated. How would I write a one-liner to recursively search all files in a project and extract the used env variables to a .env.sample file.

The one-liner bash script should ideally match all the following formats

process.env.MY_VAR
process.env.MY-VAR
process.env["MY_VAR"]
process.env['MY_VAR']
process.env[MY_VAR] // MY_VAR here being a constant which holds the actual key value

Find the unique values and print to a sample .env file which could be plugged into a pre-commit hook or pipeline.

Solution

Here is a one-liner which should work

grep -rhoP  "process\.env[\.\[](\"|\')?[A-Z0-9_\-]+(\"|\')?[\]]?" ./src \
| sed -r -n  's|^.*\.([[:upper:]0-9_-]+).*$|\1=|p' | sort --unique >  .env.sample

Breaking it down

1. grep -rhoP "process\.env[\.\[](\"|\')?[a-zA-Z0-9_\-]+(\"|\')?[\]]?" ./src

   Grep modifiers

    -P, --perl-regexp
      Enables support for PCRE regexp
      Note: OpenBSD version of grep do not support PCRE expressions, GNU grep required on MacOS  

    -r recursive
      Read all files under each directory, recursively, following symbolic links 
      only if they are on the command line.

    -o, --only-matching
      Print only the matched (non-empty) parts of a matching line, on a separate output line.

    -h, --no-filename
      Suppress the prefixing of file names on output

2. The regex process\.env[\.\[](\"|\')?[A-Z0-9_\-]+(\"|\')?[\]]?

   • Matches the string literal process.env
   • [\.\[] matches the literal "." or "["
   • (\"|\')? matches single or double quotes optionally
   • [A-Z0-9_\-]+ matches one or more the upper case, numbers , underscores and dashes
   • (\"|\')? matches single or double quotes optionally
   • [\]]? matches the literal "]" optionally

3. sort --unique we only want distinct values and sorted alphabetically (makes diff comparison easier with consistent ordered list of keys )

4. sed -r -n 's|^.*\.([[:upper:]0-9_]+).*$|\1=|p'

   • shorter version of the previous regex matching all upper case characters , numbers, dashes after the literal "s." or starting with "."
   • inserts a "=" and prints the output silently

Note This is not a foolproof or comprehensive by any means . For example it does not match small case environment variables or plenty of other methods of access for example object deconstruction like const { MY_VAR } = process.env

Answered By - Manquer

Answer Checked By - Cary Denson (WPSolving Admin)