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I know that, Shell variables are not available to the parent or child shells and Shell environments are available for child shells.

When I want to permanently add current directory to PATH I can do it in 2 ways:

1-Normal way:

 [sinoosh@localhost ~]$ vi ~/.bash_profile 

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2-without export command

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And then logout i see the same result as normal way

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there is not different between "1"&"2" . can we say the export command is useful for that time we do not want permanently add to environment variables?

What's happening here?

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    Please note that setting or changing environment variables in ~/.bash_profile does not affect the graphical environment on a desktop. Therefore I wouldn't call it the "normal way". Please take a look here: help.ubuntu.com/community/… – Gunnar Hjalmarsson Sep 25 '16 at 15:52
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The export (or declare -x) declaration makes the difference between a plain shell variable and an environment variable.

Since PATH is almost certainly already part of your environment - having been set in /etc/environment for example - marking it for export a second time isn't strictly necessary[1] (although it does no harm - and make the intent clear).


1 at least I think that's the case - I'd like to find a primary reference

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  • thank you, i think the reason is first time PATH is exported in /etc/profile but i am not sure – Sinoosh Sep 25 '16 at 13:06
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    PATH is made an environment variable early (more early than via /etc/profile, @Sinoosh) , and yes, it's not needed to export it again after that. This can possibly be derived from the community wiki page EnvironmentVariables, but it isn't expressed very clear. – Gunnar Hjalmarsson Sep 25 '16 at 15:44
  • according to the book of Ross Brunson in login shell sessions we have these steps:1-loging to shell. 2-/etc/profile is sourced 3-/etc/profile.d are sourced 4-~/.bash_profile is sourced 5-~/.bashrc is sourced from within the ~/.bash_profile 6-user conducts her business 7-exit 8-.bash_logout is sourced. do these steps are not complete? – Sinoosh Sep 25 '16 at 16:39

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