Yes, `$?` is the variable that contains the error level.

Try `echo $?` for example.

An example from Cygwin bash (I&#39;m guessing you are using Cygwin because you are using the Windows `cmd` in your example.)

    susam@nifty /cygdrive/c/Documents and Settings/susam/Desktop
    $ cmd /c &quot;badapp&quot;
    &#39;badapp&#39; is not recognized as an internal or external command,
    operable program or batch file.
    
    susam@nifty/cygdrive/c/Documents and Settings/susam/Desktop
    $ if [ $? -eq 0 ]
    &gt; then
    &gt;   echo &quot;good&quot;
    &gt; else
    &gt;   echo &quot;bad&quot;
    &gt; fi
    bad

I am currently working on a Flash webplayer with resolution switching functionality. I am trying to make use of the NetStream class&#39;s `play2()` function in Actionscript.

The problem I am running into is that the videos don&#39;t change quickly. For those familiar with the `play2()` function I believe that the player is performing a `&quot;standard switch&quot;` rather than a `&quot;fast switch.&quot;`

[The documentation says that][1] when the offset parameter is -1, fast switching occurs. What actually happens, though is once the `&quot;NetStream.Play.Transition&quot;` event is received, the player waits until the time denoted by `ns.time + ns.bufferLength` has been reached, before performing the switch.

I thought fast switching cleared the buffer, but on a check to `ns.backbufferlength`, I found that everything is still cached. Also it mentions: &quot;When offset is -1, the switch occurs at the first available keyframe after `netstream.time + 3`,&quot; which is why I am confused.

Any help/insight on this matter would be much appreciated.

Here is a snippet of code describing what is going on (`newStream()` is called when a user clicks to change to a new resolution, youtube style):

    public function newStream(address:String):void
    {
        var opts:NetStreamPlayOptions = new NetStreamPlayOptions();
        opts.streamName = address;
        opts.transition = NetStreamPlayTransitions.SWITCH;
        opts.offset = -1;
        ns.play2(opts);
    }

    private function nsCallback(event:NetStatusEvent)
    {
        switch(event.info.code)
        {
            case &quot;NetStream.Play.Transition&quot;:
            {
                trace(&quot;Current time (on Transition): &quot; + 
                      ns.time, &quot;Buffer: &quot; + ns.bufferLength);
                var estTime:Number = ns.time + ns.bufferLength;
                trace(&quot;Estimated Completion Time: &quot; + estTime);
                break;
            }
        }
    }


  [1]: http://help.adobe.com/en_US/FlashPlatform/reference/actionscript/3/flash/net/NetStreamPlayOptions.html#offset

How to make use of play2() function in order to perform fast stream switching of videos?

The web browser DOM has been around since the late &#39;90s, but it remains one of the largest constraints in performance/speed. 

We have some of the world&#39;s most brilliant minds from Google, Mozilla, Microsoft, Opera, W3C, and various other organizations working on web technologies for all of us, so obviously this isn&#39;t a simple &quot;Oh, we didn&#39;t optimize it&quot; issue.

**My question is** if i were to work on the the part of a web browser that deals specifically with this, why would I have such a hard time making it run faster?

**My question is not** asking *[what][1]* makes it slow, it&#39;s asking **[why][2]** hasn&#39;t it become faster?

This seems to be against the grain of what&#39;s going on elsewhere, such as JS engines with performance near that of C++ code.


Example of quick script:

    for (var i=0;i&lt;=10000;i++){
        someString = &quot;foo&quot;;
    }


Example of slow because of DOM:

    for (var i=0;i&lt;=10000;i++){
        element.innerHTML = &quot;foo&quot;;
    }


-----

Some details as per request:

After bench marking, it looks like it&#39;s not an unsolvable slow issue, but often the wrong tool is used, and the tool used depends on what you&#39;re doing cross-browser.

It looks like the DOM efficiency varies greatly between browsers, but my original presumption that the dom is slow and unsolvable seems to be wrong.

I ran tests against Chrome, FF4, and IE 5-9, you can see the operations per second in this chart:

![enter image description here][3]


Chrome is lightning fast when you use the DOM API, but vastly slower using the .innerHTML operator (by a magnitude 1000-fold slower), however, FF is worse than Chrome in some areas (for instance, the append test is much slower than Chrome), but the InnerHTML test runs much faster than chrome.

IE seems to actually be getting worse at using DOM append and better at innerHTML as you progress through versions since 5.5 (ie, 73ops/sec in IE8 now at 51 ops/sec in IE9).

I have the test page over here:

http://jsperf.com/browser-dom-speed-tests2

What&#39;s interesting is that it seems different browsers seem to all be having different challenges when generating the DOM. Why is there such disparity here?


  [1]: http://www.merriam-webster.com/dictionary/what
  [2]: http://www.merriam-webster.com/dictionary/why?show=0&amp;t=1311602447
  [3]: http://i.stack.imgur.com/OjUXN.jpg

But why&#39;s the browser DOM still so slow after 10 years of effort?

I have an application that only works properly when called from a windows command prompt. Something to do with the input/output streams.

So I can call it from a bash script by passing it as an argument to cmd.

cmd /c &quot;badapp&quot;   

This works fine - but occasionally badapp fails with network problems - and I get no feedback. Is there anyway to check the ERRORLEVEl from the bash script - or see the output from badapp on the terminal running the bash script? 

accessing ERRORLEVEL from bash script

I have an application that only works properly when called from a windows command prompt. Something to do with the input/output streams.
So I can call it from a bash script by passing it as an argument to cmd.
cmd /c "badapp"
This works fine - but occasionally badapp fails with network problems - and I get no feedback. Is there anyway to check the ERRORLEVEl from the bash script - or see the output from badapp on the terminal running the bash script?

I know I can test for an empty string in Bash with `-z` like so:

    if [[ -z $myvar ]]; then do_stuff; fi

but I see a lot of code written like:

    if [[ X&quot;&quot; = X&quot;$myvar&quot; ]]; then do_stuff; fi

Is that method more portable? Is it just historical cruft from before the days of `-z`? Is it for POSIX shells (even though I&#39;ve seen it used in scripts targeting `bash`)? Ready for my history/portability lesson.

----------

The same question was asked on Server Fault as [How to determine if a bash variable is empty?](https://serverfault.com/questions/7503/) but no one offered an explanation as to *why* you see code with the `X&quot;&quot;` stuff.


Test for empty string with X&quot;&quot;

I want to be able to use sed to take an input such as:

    C:\Windows\Folder\File.txt

to

    C:/Windows/Folder/File.txt

Use sed to replace all backslashes with forward slashes

I have a shell script in which I wrap a command (mvn clean install), to redirect the output  to a logfile. 

    #!/bin/bash
    ...
    mvn clean install $@ | tee $logfile
    echo $? # Does not show the return code of mvn clean install

Now if `mvn clean install` fails with an error, I want my wrapper shell script also fail with that error. But since I&#39;m piping all the output to tee, I cannot access the return code of `mvn clean install`, so when I access `$?` afterwards, it&#39;s always 0 (since tee successes). 

I tried letting the command write the error output to a separate file and checking that afterwards, but the error output of mvn is always empty (seems like it only writes to stdout).

How can I preserve the return code of `mvn clean install` but still piping the output to a logfile?

Piping command output to tee but also save exit code of command

I am having a bash script which is something like following,

    cat filename | while read line
    do
        read input;
        echo $input;
    done

but this is clearly not giving me the right output as when I do read in the while loop it tries to read from the file filename because of the possible I/O redirection.

Any other way of doing the same?

Read user input inside a loop

This does not generate any output. How come?

    $ echo &#39;this 1 2 3&#39; | grep &#39;\d\+&#39;

But these do:

    $ echo &#39;this 1 2 3&#39; | grep &#39;\s\+&#39;
    this 1 2 3
    
    $ echo &#39;this 1 2 3&#39; | grep &#39;\w\+&#39;
    this 1 2 3


Is \d not supported by grep&#39;s basic expressions?

I&#39;m fairly proficient at writing Batch scripts for Windows, but even after all these years how to correctly escape characters puzzles me.  It&#39;s especially difficult when trying figure out the correct way to escape a regular expression for use with sed. Is there any tool that can help me?  Perhaps something that allows me to paste in a &quot;normal&quot; string and it spits out the correctly escaped version of that string?

**Update:**   I&#39;m reluctant to give an example because I&#39;m not looking for an answer on how to escape one specific string. I&#39;m also not looking for a solution that will work for one specific app. I&#39;m looking for a tool that will help me get the escape syntax correct for every string I ever need to escape no matter what tool might be consuming it from the command line.  

That being said the regex I really want is 

    (^.*)(Form Product=&quot;)([^&quot;]*&quot;) FormType=&quot;[^&quot;]*&quot; FormID=&quot;([0-9][0-9]*)&quot;.*$

Take that true regex (i.e. unescaped as far as BATCH is concerned) and wrap it in some sed syntax such as `ssed &quot;s@ --- Insert escaped regex here ---      @http://psph/\1/\2@g&quot; &quot;%~1&quot;` and finally escape it... Again, is there any tool that can assist in escaping any string for use on the BATCH command line? 


p.s. There are so many exceptions to BATCH&#39;s escaping syntax that I&#39;ll even settle for a good cheat sheet.




Batch character escaping

I know that there is a post similar to this : [here][1].  
I tried using the `comp` command like it mentioned, but if I have two files, one with data like &quot;abcd&quot; and the other with data &quot;abcde&quot;, it just says the files are of different sizes. I wanted to know where exactly they differ. In Unix, the simple diff tells me which row and column, the comp command in windows works if I have something like &quot;abd&quot; and &quot;abc&quot;. Not otherwise. Any ideas what I can use for this?


  [1]: https://stackoverflow.com/questions/1011269/how-to-do-diff-r-of-unix-in-windows-cmd-prompt

What is the Windows equivalent of the diff command?

In a batch file, I have a string `abcdefg`.  I want to check if `bcd` is in the string.  

Unfortunately it seems all of the solutions I&#39;m finding search a *file* for a substring, not a string for a substring.

Is there an easy solution for this?

Batch file: Find if substring is in string (not in a file)

I want to install a file using the Windows command line. First I want to build after compiling all the .jar files to create an .apk file for an Android application without using Eclipse.

Does anyone know how this can be done without the use of Eclipse &amp; only by making use of command line.

Install an apk file from command prompt?

What is the Windows batch equivalent of the Linux shell command `echo -n` which suppresses the newline at the end of the output?

The idea is to write on the same line inside a loop.


Windows batch: echo without new line

How within a batch file to check if command

    start &quot;&quot; javaw -jar %~p0/example.jar

was successful or produced an error?

I want to use if/else statements to echo this info out.

Content Type	Original Author	Original Content on Stackoverflow
Question	shipshape	View Question on Stackoverflow
Solution 1 - Bash	Susam Pal	View Answer on Stackoverflow

accessing ERRORLEVEL from bash script

Bash Problem Overview

Bash Solutions

Solution 1 - Bash

But why's the browser DOM still so slow after 10 years of effort?

How to make use of play2() function in order to perform fast stream switching of videos?

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