variable expansion and pathname expansion

ShadeLover · 04-11-2015, 08:18 PM

Hello!

I'm in an online Intro to Unix class. We are using Fedora 20 with VirtualBox. Obviously, as this is for a class, I would normally ask the teacher. But it is an online class, and my professor generally waits a week or so before answering emails.

My question is this: What is the difference between variable expansion and pathname expansion?

I'm supposed to write a script that demonstrates that variable expansion occurs before pathname expansion. I've looked at the BASH Manual for every reference of variable expansion and pathname expansion, and two paragraphs that are in the textbook.

I think that variables on the command line are expanded first normally?

Any help would be so greatly appreciated!

veerain · 04-11-2015, 11:28 PM

It clearly says first variable expansion and at the last pathname expansion.

ShadeLover · 04-12-2015, 02:41 PM

Quote:

Originally Posted by veerain

It clearly says first variable expansion and at the last pathname expansion.

Which it? It says that variable expansion comes first and then pathname? Is there a better information source that explains this more plainly?

Diantre · 04-12-2015, 08:49 PM

Quote:

Originally Posted by ShadeLover

My question is this: What is the difference between variable expansion and pathname expansion?

I'm supposed to write a script that demonstrates that variable expansion occurs before pathname expansion. I've looked at the BASH Manual for every reference of variable expansion and pathname expansion, and two paragraphs that are in the textbook.

I think that variables on the command line are expanded first normally?

Have a look at the bash manpage, specifically the section EXPANSION:

Code:

       Expansion is performed on the command line after it has been split into words.  There are
       seven kinds of expansion performed: brace expansion, tilde expansion, parameter and vari‐
       able  expansion, command substitution, arithmetic expansion, word splitting, and pathname
       expansion.

       The order of expansions is: brace expansion, tilde  expansion,  parameter,  variable  and
       arithmetic  expansion  and  command  substitution (done in a left-to-right fashion), word
       splitting, and pathname expansion.

       On systems that can support it, there is an additional expansion available: process  sub‐
       stitution.

There is also a subsection for each type of expansion, definitely more than two paragraphs...

Here's a couple of sites that you might find useful:

http://mywiki.wooledge.org/BashGuide
http://wiki.bash-hackers.org/start

ShadeLover · 04-14-2015, 09:30 PM

Thank you Diantre!

azazalolxd · 04-22-2015, 07:22 PM

Hello. And Bye.

onebuck · 04-22-2015, 10:56 PM

@azazalolxd this is not a constructive post to this thread. You have been a member since 2013. I suggest that you re-read LQ Rules so that you can post in the correct manner.