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Martin Hope
don.joey
Asked: 2013-08-21 08:41:34 +0800 CST
  • 586

In tutorials and how-to's I often see commands combined. For instance,

sudo apt-get update && sudo apt-get install pyrenamer

There seem to be four possible connectors: &, &&, || and ;. Though the & connector is clear to me (it sends a process to the background and leaves the terminal available), it is not clear what the difference is between && and ;. And I did not know of || until Kaya's comment.

The following questions deal with the difference between the two connectors, but do so mostly in the comments:

So here are a number of related questions:

  1. What is the difference between ; and &&?
  2. When should you use them respectively? It would be nice to see some use cases: if I want to run a command and then after it shutdown my computer, which connector should I choose?
  3. What are their advantages and dangers? Robie Basak mentions in a comment to this answer that a command like cd /somewhere_else; rm -Rf * can have destructive consequences if the first element in the command chain fails, for instance.
  4. If relevant, where do they come from?
command-line
Martin Hope
huff
Asked: 2011-08-27 16:22:54 +0800 CST
  • 594

I'm running Ubuntu 11.04. I use the terminal to start a bash session, and I want to add an environment variable:

$r@hajt:~$ env THEVAR=/example

But it's not working. It shows all the variables with THEVAR being the last one, but another call to env does not show THEVAR anymore- env | grep THEVAR returns nothing.

Similarly, scripts with export (export THEVAR=/example) or other variable assignments (THEVAR=/example) don't add the environment variable.

I know I'm doing something wrong, I know it should be something simple, but I just can't find what.

UPDATE: The real meaning of my question was this one:

(Anyway I'll choose the most voted answer and leave the edited title -that wasn't what I was asking)

env runs a program in a modified environment, then dismisses all the changes.

bash
Martin Hope
Benjamin
Asked: 2011-08-08 00:04:12 +0800 CST
  • 574

I want to install Oracle's JRE and to update to the latest version with the Software Updater when they released. Is there a Ubuntu package that is provided by Canonical or Oracle?

Before release Java 7, I followed this way to install Java 6.

But it doesn't work for Java 7. There is no package sun-java7-xxx. How can you install Java 7?

java
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