Why do bash environment variables differ in shell versus node?

Question

Run these commands in Bash:

1. NODE_ENV=production echo $NODE_ENV outputs ""

2. NODE_ENV=production && echo $NODE_ENV outputs "production"

3. export NODE_ENV=production && echo $NODE_ENV outputs "production"

Now there is a file index.js:

console.log(process.env.NODE_ENV)

then run these commands in Bash:

4. NODE_ENV=production node index.js outputs "production"

5. NODE_ENV=production && node index.js outputs "undefined"

6. export NODE_ENV=production && node index.js outputs "production"

I get confused by these commands, why are the results different?

Edit:

Thanks everyone. Now I give my explanations, maybe it's helpful for other guys.

NODE_ENV=production echo $NODE_ENV, Bash expends $NODE_ENV before running this command, at this point $NODE_ENV is not set so the result is blank.

NODE_ENV=production && echo $NODE_ENV, these are two commands, the second command command only runs if the first command succeeds. Before running the second command Bash expends $NODE_ENV which is set at this point.

NODE_ENV=production node index.js, prefixing a variable definition to a command makes this variable available to this command.

NODE_ENV=production && node index.js, node is an external commands, Bash forks it and runs it in a sub-process, node doesn't get $NODE_ENV from parent process.

export NODE_ENV=production && node index.js, export makes the variable available to sub-processes, so node gets $NODE_ENV.

Answer 1

Few points first:

• && is a logical operator that separates two commands (the second one runs only if the first one succeeds)

• For var=value some_command, the variable var is passed to the environment of some_command, only after shell performs all expansions on some_command

Now:

• NODE_ENV=production echo $NODE_ENV: shell runs echo $NODE_ENV first and NODE_ENV is unset while running and hence the output is blank; the variable NODE_ENV=production can only be passed to the expanded environment like i told earlier

• NODE_ENV=production && echo $NODE_ENV has two commands; as the declaration comes in the first (and succeeds) and hence NODE_ENV will have the value production in the second command. Note that, the variable NODE_ENV will not be passed to the expanded environment of the second command.

• export NODE_ENV=production && echo $NODE_ENV is like the above with the fact that you are making NODE_ENV available throughout the environment (all subprocesses) by exporting-ing. Hence the variable will be available to the second command in the expansion time and also to its environment.

Similar logics apply to the node commands (and all other alike cases) too.