BASH: difference between "export k=1" vs. "k=1"

Question

I am going to write an script and It looks there is no difference between:

export k=1 

and

k=1 

Am I right?

Answer 1

export makes the variable available to subprocesses.

That is, if you spawn a new process from your script, the variable k won't be available to that subprocess unless you export it. Note that if you change this variable in the subprocess that change won't be visible in the parent process.

See section 3.2.3 of this doc for more detail.

Answer 2

I've created a simple script to show the difference:

$ cat script.sh  echo $answer 

Let's test without export

$ answer=42 $ ./script.sh   $ . script.sh  42 

The value is known only if using the same process to execute the script (that is, the same bash instance, using source / .)

Now, using export:

$ export answer=42 $ ./script.sh  42 $ . script.sh  42 

The value is known to the subprocess.

Thus, if you want the value of a variable to be known by subprocesses then you should use export.