The `&amp;&amp;` operator is a boolean AND operator: if the left side returns a non-zero exit status, the operator returns that status and does not evaluate the right side (it short-circuits), otherwise it evaluates the right side and returns its exit status.  This is commonly used to make sure that `command2` is only run if `command1` ran successfully.

The `;` token just separates commands, so it will run the second command regardless of whether or not the first one succeeds.

## command1 &amp;&amp; command2
`command1 &amp;&amp; command2` executes `command2` if (and only if) `command1` execution ends up successfully.  In Unix jargon, that means *exit code* / *return code* equal to zero. 
## command1; command2
`command1; command2` executes `command2` after executing `command1`, sequentially.  It does not matter whether the commands were successful or not. 

The former is a simple logic `AND` using short circuit evaluation, the latter simply delimits two commands.

What happens in real is that when the first program returns a nonzero exit code, the whole `AND` is evaluated to `FALSE` and the second command won&#39;t be executed. The later simply executes them both in order.

First of all, [this question][1] asks a very similar question. However, my question has a subtle difference.

What I&#39;d like to know is whether it is possible to programmatically change the `colorPrimary` attribute of a theme to an ***arbitrary*** color?

So for example, we have:

    &lt;style name=&quot;AppTheme&quot; parent=&quot;android:Theme.Material.Light&quot;&gt;
        &lt;item name=&quot;android:colorPrimary&quot;&gt;#ff0000&lt;/item&gt;
        &lt;item name=&quot;android:colorAccent&quot;&gt;#ff0000&lt;/item&gt;
    &lt;/style&gt;

At runtime, the user decides he wants to use `#ccffff` as a primary color. Ofcourse there&#39;s no way I can create themes for all possible colors.

I don&#39;t mind if I have to do hacky stuff, like relying on Android&#39;s private internals, as long as it works using the public SDK.

My goal is to eventually have the `ActionBar` *and* all widgets like a `CheckBox` to use this primary color.


  [1]: https://stackoverflow.com/questions/25354558/how-to-change-programmatically-the-primary-color-in-android-l

How to _really_ programmatically change primary and accent color in Android Lollipop?

Suppose I want to have REST endpoints which look roughly like this:

    /user/
    /user/user_id 
    
    /user/user_id/items/
    /user/user_id/items/item_id

CRUD on each if makes sense. For example, /user POST creates a new user, GET fetches all users. /user/*user_id* GET fetches just that one user.

Items are user specific so I put them under *user_id*, which is a particular user.

Now to make Express routing modular I made a few router instances. There is a router for user, and a router for the item.

    var userRouter = require(&#39;express&#39;).Router();
    userRouter.route(&#39;/&#39;)
      .get(function() {})
      .post(function() {})
    userRouter.route(&#39;/:user_id&#39;)
      .get(function() {})
    
    var itemRouter = require(&#39;express&#39;).Router();
    itemRouter.route(&#39;/&#39;)
      .get(function() {})
      .post(function() {})
    itemRouter.route(&#39;/:item_id&#39;)
      .get(function() {})
    
    app.use(&#39;/users&#39;, userRouter);
    
    // Now how to add the next router?
    // app.use(&#39;/users/&#39;, itemRouter);

URL to `item` is descendents of the URL hierarchy of the `user`. Now how do I get URL with `/users` whatever to userRouter but the more specific route of `/user/*user_id*/items/` to the itemRouter? And also, I would like user_id to be accessible to itemRouter as well, if possible.


Rest with Express.js nested router

What is the difference between ampersand and semicolon in Linux [Bash][1]?

For example,

    $ command1 &amp;&amp; command2

vs

    $ command1; command2

  [1]: http://en.wikipedia.org/wiki/Bash_%28Unix_shell%29


What is the difference between double-ampersand (&amp;&amp;) and semicolon (;) in Linux Bash?

What is the difference between ampersand and semicolon in Linux <a href="http://en.wikipedia.org/wiki/Bash_%28Unix_shell%29" target="_blank" rel="noopener noreferrer">Bash</a>?
For example,
<pre><code class="hljs language-ruby">$ command1 &#x26;&#x26; command2
</code></pre>
vs
<pre><code class="hljs language-ini">$ command1; command2
</code></pre>

I&#39;m trying to find files with specific extensions. 
For example, I want to find all .pdf and .jpg files that&#39;s named Robert

I know I can do this command 

    $ find . -name &#39;*.h&#39; -o -name &#39;*.cpp&#39;

but I need to specify the name of the file itself besides the extensions. 
I just want to see if there&#39;s a possible way to avoid writing the file name again and over again
Thank you !

Recursively find files with a specific extension

Each time, when I manually run `tcpdump`, I have to use &lt;kbd&gt;Ctrl&lt;/kbd&gt;+&lt;kbd&gt;C&lt;/kbd&gt; to stop it. Now I want to schedule my `tcpdump` with cronjob and I only need it to run for 1 and half hours. Without manually running &lt;kbd&gt;Ctrl&lt;/kbd&gt;+&lt;kbd&gt;C&lt;/kbd&gt; or kill command, how can it be stopped automatically? Here is the command I am testing:

    tcpdump -i eth0 &#39;port 8080&#39; -w  myfile

I can schedule another cronjob  to kill the `tcpdump` process, but it seems not a good idea. 

How to schedule tcpdump to run for a specific period of time?

How to get only the  process ID for a specified process name in linux?

    ps -ef|grep java    
    test 31372 31265  0 13:41 pts/1    00:00:00 grep java

Based on the process id I will write some logic. So how do I get only the process id for a specific process name. 

Sample program:

    PIDS= ps -ef|grep java
    if [ -z &quot;$PIDS&quot; ]; then
    echo &quot;nothing&quot;
    else
    mail test@domain.com
    fi




How to get only process ID in specify process name in linux?

When using `grep` in linux, the result often contains a lot of &quot;binary file XXX matches&quot;, which I do not care about. How to suppress this part of the results, or how to exclude binary files in grep?

How to suppress binary file matching results in grep

This is really just to satisfy curiosity, and see if there&#39;s a better way to do this.

On my Windows 8 box, Node&#39;s `process.env` object has a `NUMBER_OF_PROCESSORS` property, on my Linux box it doesn&#39;t.

Obviously different platforms have different environment variables, that much is a given, but it seems like NUMBER_OF_PROCESSORS would be a useful thing to have regardless.

My quick fix for Linux was spawning a child process to run the `nproc` command, but I&#39;d like to avoid using a callback for simply getting the number of processors. Seems like there must be a simpler way.

What have other people done to solve this?

Node.js - Get number of processors available

Traditionally MSYS bash has been considered inferior to Cygwin bash. 
The former was an ancillary tool inside MinGW intended for running autoconf scripts. 
But now there is  MinGW-w64 and MSYS2. The latter ships with a sweet pacman like package manager and elegant shells like zsh, so I wonder if there is still a gap in the emulation layer. 

While MinGW* applications are Windows native executables, MSYS2 software requires a POSIX-emulation layer, just like Cygwin does. At least to a casual user, it is hard to spot the differences between the two. 

- Which are the functional differences between the two emulation layers (if any)? 
- Which emulation is faster (more efficient)?

 



Differences between MSYS2 and Cygwin

A recent vulnerability, [CVE-2014-6271][1], in how [Bash][2] interprets environment variables [was disclosed][3]. The exploit relies on Bash parsing some environment variable declarations as function definitions, but then continuing to execute code following the definition:

    $ x=&#39;() { echo i do nothing; }; echo vulnerable&#39; bash -c &#39;:&#39;
    vulnerable

But I don&#39;t get it. There&#39;s nothing I&#39;ve been able to find in the Bash manual about interpreting environment variables as functions at all (except for _inheriting functions_, which is different). Indeed, a proper named function definition is just treated as a value:

    $ x=&#39;y() { :; }&#39; bash -c &#39;echo $x&#39;
    y() { :; }

But a corrupt one prints nothing:

    $ x=&#39;() { :; }&#39; bash -c &#39;echo $x&#39;

    $ # Nothing but newline

The corrupt function is unnamed, and so I can&#39;t just call it. Is this vulnerability a pure implementation bug, or is there an intended feature here, that I just can&#39;t see?
 
## Update

Per Barmar&#39;s comment, I hypothesized the name of the function was the parameter name:

    $ n=&#39;() { echo wat; }&#39; bash -c &#39;n&#39;
    wat

Which I could swear I tried before, but I guess I didn&#39;t try hard enough. It&#39;s repeatable now. Here&#39;s a little more testing:

    $ env n=&#39;() { echo wat; }; echo vuln&#39; bash -c &#39;n&#39;
    vuln
    wat
    $ env n=&#39;() { echo wat; }; echo $1&#39; bash -c &#39;n 2&#39; 3 -- 4
    
    wat

…so apparently the args are not set at the time the exploit executes.

Anyway, the basic answer to my question is, _yes, this is how Bash implements inherited functions_.

  [1]: http://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2014-6271
  [2]: http://en.wikipedia.org/wiki/Bash_%28Unix_shell%29
  [3]: https://securityblog.redhat.com/2014/09/24/bash-specially-crafted-environment-variables-code-injection-attack/


Is the behavior behind the Shellshock vulnerability in Bash documented or at all intentional?


I am supposed to set the EC2_HOME and JAVA_HOME variables
before running a command (ec2-describe-regions)

How do I do that in one go?


How set multiple env variables for a bash command

I have a massive prompt taking my Terminal&#39;s space &quot;*name*s-MacBook-Pro&quot; on the same line where the command is entered on every line. 

Is there a way I can remove this or make it shorter?


Content Type	Original Author	Original Content on Stackoverflow
Question	stevek-pro	View Question on Stackoverflow
Solution 1 - Linux	cdhowie	View Answer on Stackoverflow
Solution 2 - Linux	jimm-cl	View Answer on Stackoverflow
Solution 3 - Linux	Danstahr	View Answer on Stackoverflow

What is the difference between double-ampersand (&&) and semicolon (;) in Linux Bash?

Linux Problem Overview

Linux Solutions

Solution 1 - Linux

Solution 2 - Linux

command1 && command2

command1; command2

Solution 3 - Linux

Rest with Express.js nested router

How to _really_ programmatically change primary and accent color in Android Lollipop?

Attributions