Meaning of `export PATH=…` in .bash_profile

Question

I'm using a mac for some years now and as I'm currently learning ruby on rails, I felt like I should learn more about the system I'm using. I took a look at the ~/.bash_profile, it looks like this

PATH="/Users/nikolajandersen/.apportable/SDK/bin:$PATH"

[[ -s "$HOME/.rvm/scripts/rvm" ]] && source "$HOME/.rvm/scripts/rvm" # Load RVM$

# Setting PATH for Python 3.3
# The orginal version is saved in .bash_profile.pysave
PATH="/Library/Frameworks/Python.framework/Versions/3.3/bin:${PATH}"
export PATH
export PATH=/usr/local/bin:$PATH
export PATH=/usr/local/bin:$PATH

As there are two identical export PATH=/usr/local/bin:$PATH lines, I tried to delete the one. As a result, commands like nano and ls didn't work anymore. I reverted the change but I don't understand why it has to stated two times.

Another question is: why does it sometimes $PATH and sometimes just PATH without the $? Why does -s "$HOME/.rvm/scripts/rvm" stand in [[ ]] braces? And what does export PATH do?

Update This is the output of echo $PATH

/usr/local/bin:/usr/local/bin:/Library/Frameworks/Python.framework/Versions/3.3/bin:/Users/nikolajandersen/.rvm/gems/ruby-2.0.0-p353/bin:/Users/nikolajandersen/.rvm/gems/ruby-2.0.0-p353@global/bin:/Users/nikolajandersen/.rvm/rubies/ruby-2.0.0-p353/bin:/Users/nikolajandersen/.rvm/bin:/Users/nikolajandersen/.apportable/SDK/bin:/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin:/opt/sm/bin:/opt/sm/pkg/active/bin:/opt/sm/pkg/active/sbin

It seems like you were right with the newline. I deleted the line again and made sure that there is a blank line in the end. Now the commands are still working.

Solution

The PATH before = is a variable name and the combination tells bash to store the stuff behind the = in the variable.
The $PATH is the value of the variable PATH up until then.

The combination PATH="some_path_to_stuff:$PATH" extends the PATH variable. In bash this is a colon (:) separated list.

---

Regarding the double addition of /usr/local/bin, I can only guess that the second version has no newline after it (and is at the end of the file). In principle this should give you a PATH which starts with /usr/local/bin:/usr/local/bin:..... You can check that with

echo $PATH

And if there is only one time /usr/local/bin then do:

echo "" >> ~/.bash_profile

and login an try to print $PATH again.

Comments

[terdon]

Please don't combine multiple questions in a single post. The issue with PATH vs $PATH is explained here, and [[ ]] is a test operator, it basically means if. The duplicate exports should have no effect, that's weird, I recommend you focus on that one and make you question about the export.

[Shoeb]

Ok, sorry for the multiple questions and thanks for the answers.

[Bananguin]

Welcome to the bright side! Before we google, we like to read manuals, called man pages. Bash's man page (man bash) can answer all your questions.

[terdon]

@Bananguin in the OP's defense, man bash is 5465 lines long, not the easiest of reads.

[Shoeb]

Thanks for the additional info. I updated my question with the echo $PATH output. It looks a little weird.