So to make your expression work, changing `&amp;&amp;` for `-a` will do the trick.

It is correct like this:

     if [ -f $VAR1 ] &amp;&amp; [ -f $VAR2 ] &amp;&amp; [ -f $VAR3 ]
     then  ....

or like

     if [[ -f $VAR1 &amp;&amp; -f $VAR2 &amp;&amp; -f $VAR3 ]]
     then  ....

or even

     if [ -f $VAR1 -a -f $VAR2 -a -f $VAR3 ]
     then  ....


You can find further details in this question https://stackoverflow.com/q/2309849/1983854 and some references given there like [What is the difference between test, \[ and \[\[ ?][1].


  [1]: http://mywiki.wooledge.org/BashFAQ/031

Imagine the following scenario: `Project A` is a shared library which has several dependencies (`LibA`, `LibB`, and `LibC`). `Project B` is an executable that has a dependency on `project A`, and therefore requires all of `Project A`&#39;s dependencies also in order to build.

Additionally, both projects are built using `CMake`, and `Project A` should not need to be installed (via the &#39;install&#39; target) in order for `Project B` to use it, as this can become a nuisance to developers.

What is the best way to solve these dependencies using `CMake`? The ideal solution would be as simple as possible (though no simpler) and require minimal maintenance.


CMake and finding other projects and their dependencies

Why do Double.parseDouble(null) and Integer.parseInt(null) throw different exceptions?

Is this a historical accident or intentional? The documentation clearly states two types of exceptions for [`Double.parseDouble(...)`][1] and one for [`Integer.parseInt()`][2], but it seems inconsistent:

    Integer.parseInt(null); // throws java.lang.NumberFormatException: null

However 

    Double.parseDouble(null); // throws java.lang.NullPointerException

  [1]: http://docs.oracle.com/javase/7/docs/api/java/lang/Double.html#parseDouble%28java.lang.String%29
  [2]: http://docs.oracle.com/javase/7/docs/api/java/lang/Integer.html#parseInt%28java.lang.String%29


Why do Double.parseDouble(null) and Integer.parseInt(null) throw different exceptions?

I have three variables:

    VAR1=&quot;file1&quot;
    VAR2=&quot;file2&quot;
    VAR3=&quot;file3&quot;

How to use and (`&amp;&amp;`) operator in if statement like this:

    if [ -f $VAR1 &amp;&amp; -f $VAR2 &amp;&amp; -f $VAR3 ]
       then ...
    fi

When I write this code it gives error. What is the right way?

Using the &amp;&amp; operator in an if statement

I have three variables:
<pre><code class="hljs language-ini">VAR1="file1"
VAR2="file2"
VAR3="file3"
</code></pre>
How to use and (<code>&#x26;&#x26;</code>) operator in if statement like this:
<pre><code class="hljs language-bash">if [ -f $VAR1 &#x26;&#x26; -f $VAR2 &#x26;&#x26; -f $VAR3 ]
 then ...
fi
</code></pre>
When I write this code it gives error. What is the right way?

As we know, in bash programming the way to pass arguments is `$1`, ..., `$N`. However, I found it not easy to pass an array as an argument to a function which receives more than one argument. Here is one example:

    f(){
     x=($1)
     y=$2
    
     for i in &quot;${x[@]}&quot;
     do
      echo $i
     done
     ....
    }

    a=(&quot;jfaldsj jflajds&quot; &quot;LAST&quot;)
    b=NOEFLDJF
    
    f &quot;${a[@]}&quot; $b
    f &quot;${a[*]}&quot; $b

As described, function `f `receives two arguments: the first is assigned to `x` which is an array, the second to `y`.

`f` can be called in two ways. The first way use the `&quot;${a[@]}&quot;` as the first argument, and the result is:

    jfaldsj 
    jflajds

The second way use the `&quot;${a[*]}&quot;` as the first argument, and the result is:

    jfaldsj 
    jflajds 
    LAST

Neither result is as I wished. So, is there anyone having any idea about how to pass array between functions correctly?

How to pass array as an argument to a function in Bash

I want to call `myscript` file in this way:

    $ ./myscript -s 45 -p any_string

or

    $ ./myscript -h  #should display help
    $ ./myscript     #should display help

My requirements are:

 - `getopt` here to get the input arguments
 - check that `-s` exists, if not return an error
 - check that the value after the `-s` is 45 or 90
 - check that the `-p` exists and there is an input string after
 - if the user enters `./myscript -h` or just `./myscript` then display help

I tried so far this code:

    #!/bin/bash
    while getopts &quot;h:s:&quot; arg; do
      case $arg in
        h)
          echo &quot;usage&quot; 
          ;;
        s)
          strength=$OPTARG
          echo $strength
          ;;
      esac
    done

But with that code I get errors.  How to do it with Bash and `getopt`?

An example of how to use getopts in bash

I&#39;m wondering how to declare a 2D array in bash and then initialize to 0.

In C it looks like this:

    int a[4][5] = {0};

And how do I assign a value to an element? As in C:

    a[2][3] = 3;

How to declare 2D array in bash

What is the best way to emulate a do-while loop in Bash?

I could check for the condition before entering the `while` loop, and then continue re-checking the condition in the loop, but that&#39;s duplicated code. Is there a cleaner way?

Pseudo code of my script:

    while [ current_time &lt;= $cutoff ]; do
        check_if_file_present
        #do other stuff
    done

This doesn&#39;t perform `check_if_file_present` if launched after the `$cutoff` time, and a do-while would.



Emulating a do-while loop in Bash

It seems that newer versions of bash have the `&amp;&gt;` operator, which (if I understand correctly), redirects both stdout and stderr to a file (`&amp;&gt;&gt;` appends to the file instead, as Adrian clarified). 

What&#39;s the simplest way to achieve the same thing, but instead piping to another command?

For example, in this line:

    cmd-doesnt-respect-difference-between-stdout-and-stderr | grep -i SomeError

I&#39;d like the grep to match on content both in stdout and stderr (effectively, have them combined into one stream).

*Note*: this question is asking about piping, *not* redirecting - so it is not a duplicate of the question it&#39;s currently marked as a duplicate of.

Piping both stdout and stderr in bash?

I have a data frame taken from a .csv-file which contains numeric and character values. I want to convert this data frame into a matrix. All containing information is numbers (the non-number-rows I deleted), so it should be possible to convert the data frame into a numeric matrix. However, I do get a character matrix.

I found the only way to solve this is to use `as.numeric` for each and every row, but this is quite time-consuming. I am quite sure there is a way to do this with some kind of `if(i in 1:n)`-form, but I cannot figure out how it might work. Or is the only way really to already start with numeric values, like proposed here(https://stackoverflow.com/questions/8052828/making-matrix-numeric-and-name-orders)?

Probably this is a very easy thing for most of you :P

The matrix is a lot bigger, this is only the first few rows... Here&#39;s the code: 

    cbind(
    as.numeric(SFI.Matrix[ ,1]),
    as.numeric(SFI.Matrix[ ,2]),
    as.numeric(SFI.Matrix[ ,3]),
    as.numeric(SFI.Matrix[ ,4]),
    as.numeric(SFI.Matrix[ ,5]),
    as.numeric(SFI.Matrix[ ,6]))  
    
    # to get something like this again:

    Social.Assistance Danger.Poverty GINI S80S20 Low.Edu        Unemployment 
    0.147             0.125          0.34    5.5   0.149        0.135 0.18683691
    0.258             0.229          0.27    3.8   0.211        0.175 0.22329362
    0.207             0.119          0.22    3.1   0.139        0.163 0.07170422
    0.219             0.166          0.25    3.6   0.114        0.163 0.03638525
    0.278             0.218          0.29    4.1   0.270        0.198 0.27407825
    0.288             0.204          0.26    3.6   0.303        0.211 0.22372633



Thank you for any help!

Right way to convert data.frame to a numeric matrix, when df also contains strings?

I have a python script that can receive either zero or three command line arguments. (Either it runs on default behavior or needs all three values specified.)

What&#39;s the ideal syntax for something like:

    if a and (not b or not c) or b and (not a or not c) or c and (not b or not a):

?

Python syntax for &quot;if a or b or c but not all of them&quot;

Can I somehow use if-then-else construction (ternary-operator) in angularjs expression, for example I have function $scope.isExists(item) that has to return bool value.
I want something like this,

    &lt;div ng-repeater=&quot;item in items&quot;&gt;
        &lt;div&gt;{{item.description}}&lt;/div&gt;
        &lt;div&gt;{{isExists(item) ? &#39;available&#39; : &#39;oh no, you don&#39;t have it&#39;}}&lt;/div&gt;
    &lt;/div&gt;

I know that I can use function that returns string, I&#39;m interesting in possibility of using if-then-else construction into expression.
Thanks.

Angularjs if-then-else construction in expression

I&#39;ve got a in if-elif-elif-else statement in which 99% of the time, the else statement is executed:

    if something == &#39;this&#39;:
        doThis()
    elif something == &#39;that&#39;:
        doThat()
    elif something == &#39;there&#39;:
        doThere()
    else:
        doThisMostOfTheTime()

This construct is done **a lot**, but since it goes over every condition before it hits the else I have the feeling this is not very efficient, let alone Pythonic. On the other hand, it does need to know if any of those conditions are met, so it should test it anyway.

Does anybody know if and how this could be done more efficiently or is this simply the best possible way to do it?

Most efficient way of making an if-elif-elif-else statement when the else is done the most?

Using SASS, I would like to have multiple condition in IF statement 

__What I use right now :__

    @function color-x ($alpha) {
        @if      $accent == red   {@return red($alpha)} 
        @else if $accent == green {@return green($alpha)} 
        @else if $accent == blue  {@return blue($alpha)}
    }

__My naive (failed) attempt to use multiple conditions :__

    @function color-x ($alpha) {
        @if      $accent == red   &amp;&amp; theme == light {@return red($alpha)} 
        @else if $accent == green &amp;&amp; theme == light {@return green($alpha)} 
        @else if $accent == blue  &amp;&amp; theme == light {@return blue($alpha)}
    }

Is it possible to have multiple conditions?


Using multiple conditions (AND) in SASS IF statement

I haven&#39;t been able to figure out what the `&gt;&gt;&gt;` does, even though I often see it often in source code.

What do the three arrow (&quot;&gt;&gt;&gt;&quot;) signs mean?

Lately I was playing with google&#39;s new programming language [Go][1] and was wondering why the assignment operator `:=` has a *colon* in front of the equal sign `=`.

Is there a particular reason why the authors of the language wanted to use `name := &quot;John&quot;` instead of `name = &quot;John&quot;`?

[1]: http://golang.org/

Assignment operator in Go language

I am confused about a bash script.

I have the following code:

    function grep_search() {
        magic_way_to_define_magic_variable_$1=`ls | tail -1`
        echo $magic_variable_$1
    }

I want to be able to create a variable name containing the first argument of the command and bearing the value of e.g. the last line of `ls`.

So to illustrate what I want:

    $ ls | tail -1
    stack-overflow.txt
    
    $ grep_search() open_box
    stack-overflow.txt

So, how should I define/declare `$magic_way_to_define_magic_variable_$1` and how should I call it within the script?

I have tried `eval`, `${...}`, `\$${...}`, but I am still confused.

Dynamic variable names in Bash

I&#39;m trying to use in Python 3.3 an old library (dating from 2003!). When I import it, Python throws me an error because there are `&lt;&gt;` signs in the source file, e.g.:

    if (cnum &lt; 1000 and nnum &lt;&gt; 1000 and ntext[-1] &lt;&gt; &quot;s&quot;:
        ...

I guess it&#39;s a now-abandoned sign in the language.

What exactly does it mean, and which (more recent) sign should I replace it with?


What does `&lt;&gt;` mean in Python?

How can I convert  `Map&lt;String,Object&gt;` to `Map&lt;String,String&gt;` ?

This does not work:

    Map&lt;String,Object&gt; map = new HashMap&lt;String,Object&gt;(); //Object is containing String
    Map&lt;String,String&gt; newMap =new HashMap&lt;String,String&gt;(map);



Convert Map&lt;String,Object&gt; to Map&lt;String,String&gt;

I&#39;m using maps for the first time and I realized that there are many ways to insert an element. You can use `emplace()`, `operator[]` or `insert()`, plus variants like using `value_type` or `make_pair`. While there is a lot of information about all of them and questions about particular cases, I still can&#39;t understand the big picture.
So, my two questions are:

 1. What is the advantage of each one of them over the others?

 2. Was there any need for adding emplace to the standard? Is there anything that wasn&#39;t possible before without it?

insert vs emplace vs operator[] in c++ map

What is the difference between exclamation mark (`!`) and question mark (`?`) when sending messages to Actors?

    myActor ! Hello(value1)
    myActor ? Hello(value1)

Akka in Scala, exclamation mark and question mark

What is difference between `!=` and `&lt;&gt;` operators in Sql Server? 

Since both are used as `not` operator. E.g :

    select * from TableName where ColName &lt;&gt; value

or 

    select * from TableName where ColName != value

returns same values (Rows).


What is difference between != and &lt;&gt; in sql server

Consider the following snippet:

    &quot;12-18&quot; -Contains &quot;-&quot;

You’d think this evaluates to `true`, but it doesn&#39;t. This will evaluate to `false` instead. I’m not sure why this happens, but it does.

To avoid this, you can use this instead:

    &quot;12-18&quot;.Contains(&quot;-&quot;)

Now the expression will evaluate to true.

Why does the first code snippet behave like that? Is there something special about `-` that doesn&#39;t play nicely with `-Contains`? [The documentation][1] doesn&#39;t mention anything about it.

  [1]: http://technet.microsoft.com/en-us/library/hh847759.aspx


Content Type	Original Author	Original Content on Stackoverflow
Question	Ziyaddin Sadigov	View Question on Stackoverflow
Solution 1 - Bash	fedorqui	View Answer on Stackoverflow

Using the && operator in an if statement

Bash Problem Overview

Bash Solutions

Solution 1 - Bash

Why do Double.parseDouble(null) and Integer.parseInt(null) throw different exceptions?

CMake and finding other projects and their dependencies

Attributions