Understanding and Creating Windows PowerShell 1.0 Variables - Revision history

Neil: Text replacement - " " to "
"
2016-10-27T20:16:24Z
Text replacement - "<table border="0" cellspacing="0"> " to "<table border="0" cellspacing="0" width="100%">"

← Older revision Revision as of 20:16, 27 October 2016
Line 1: Line 1:

−
<table border="0" cellspacing="0">
+
<table border="0" cellspacing="0" width="100%"><tr>

−
<tr>
+

<td width="20%">[[Directing and Formatting Windows PowerShell 1.0 Output|Previous]]<td align="center">[[Windows PowerShell 1.0 Essentials|Table of Contents]]<td width="20%" align="right">[[Basic Windows PowerShell 1.0 Types|Next]]</td>

<td width="20%">[[Directing and Formatting Windows PowerShell 1.0 Output|Previous]]<td align="center">[[Windows PowerShell 1.0 Essentials|Table of Contents]]<td width="20%" align="right">[[Basic Windows PowerShell 1.0 Types|Next]]</td>

<tr>

<tr>

Neil: Text replacement - "" to "
"
2016-05-05T14:43:56Z
Text replacement - "<table border="0" cellspacing="0" width="100%">" to "<table border="0" cellspacing="0">"

← Older revision Revision as of 14:43, 5 May 2016
Line 1: Line 1:

−
<table border="0" cellspacing="0" width="100%">
+
<table border="0" cellspacing="0">

<tr>

<tr>

<td width="20%">[[Directing and Formatting Windows PowerShell 1.0 Output|Previous]]<td align="center">[[Windows PowerShell 1.0 Essentials|Table of Contents]]<td width="20%" align="right">[[Basic Windows PowerShell 1.0 Types|Next]]</td>

<td width="20%">[[Directing and Formatting Windows PowerShell 1.0 Output|Previous]]<td align="center">[[Windows PowerShell 1.0 Essentials|Table of Contents]]<td width="20%" align="right">[[Basic Windows PowerShell 1.0 Types|Next]]</td>

Neil: Text replacement - "BUY_WPS" to "powershell"

2016-02-01T21:12:12Z

Text replacement - "<google>BUY_WPS</google>" to "<htmlet>powershell</htmlet>"

Neil: Text replacement - "ADSDAQBOX_FLOW" to "adsdaqbox_flow"

2016-02-01T18:07:50Z

Text replacement - "<google>ADSDAQBOX_FLOW</google>" to "<htmlet>adsdaqbox_flow</htmlet>"

Neil at 19:14, 14 May 2009

2009-05-14T19:14:34Z

Neil at 13:36, 14 May 2009

2009-05-14T13:36:32Z

Neil: /* Naming a Variable in PowerShell */

2009-03-18T18:12:27Z

‎Naming a Variable in PowerShell

Neil: /* Pre-defined PowerShell Variables */

2008-11-17T21:12:40Z

‎Pre-defined PowerShell Variables

Neil: /* Changing the Type of a PowerShell Variable */

2008-11-17T21:10:07Z

‎Changing the Type of a PowerShell Variable

Show changes

Neil: New page: A large part of writing scripts, and for that matter programming in general, involves the handling and manipulation of data. Data can take many forms, ranging from single characters, words...

2008-11-17T20:37:22Z

New page: A large part of writing scripts, and for that matter programming in general, involves the handling and manipulation of data. Data can take many forms, ranging from single characters, words...

New page

A large part of writing scripts, and for that matter programming in general, involves the handling and manipulation of data. Data can take many forms, ranging from single characters, words and sentences to integers, floating point numbers and true and false values. In object-based scripting environments such as Windows PowerShell, data can also take the form of an ''object'', a self contained module which is capable of encapsulating any number of data values of numerous different types.

When working with data values in PowerShell, we need some convenient way to store these values so that we can easily access them and make reference to them whenever necessary. This is where PowerShell variables come in.

It is often useful to think of variables as computer memory locations where data is to be stored. When declaring a variable in PowerShell, it is assigned a name that can used to reference it in other locations in the PowerShell script. The value of the variable can be accessed, the value can be changed, and the type of variable can be altered all by referencing the name assigned at variable creation time.

== Naming a Variable in PowerShell ==

In PowerShell, all variable names must begin the dollar sign ($). In general any string comprising numbers and letters and pre-fixed with a $ can be used as a variable name, with the exception of pre-defined variable names and $_.

Let's look at some valid and invalid PHP variable names:

<pre>
$myName # valid
$_myvar # valid
$myVar21 # valid
$1greatvariable #valid
$mystring-1 # invalid - contains a non-alphanumeric character (-)
$mystring+1 # invalid - contains a non-alphanumeric character (+)
</pre>

Variable names in PowerShell are case-insensitive. This means that PowerShell considers ''$myvariable'' to be the same variable name as ''''$MyVariable''.

== Creating and Assigning a Value to a PowerShell Variable ==

Values are assigned to variables using the PowerShell ''assignment operator'', represented by the ''='' sign. To assign a value to a variable therefore, the variable name is placed on the left of the expression, followed by the assignment operator. The value to be assigned is then placed to the right of the assignment operator.

PowerShell is a loosely typed language. In contract to ''strongly'' typed languages such as C#, C++ or Java this means that the ''type'' of the variable does not need to be specified at creation time. Instead, PowerShell infers the type from the data being assigned. For example, let's begin by assigning the word "Red" to a variable named mycolor:

<pre>
$mycolor = "Red";
</pre>

We have now declared a variable with the name ''mycolor'' and assigned a string value to it of "Red". Since "Red" is clearly a string, PowerShell safely assumes the variable is of type ''string''.

We can similarly declare a variable to contain an integer value:

<pre>
$numberofcolors = 6;
</pre>

The above assignment creates a variable named ''numberofcolors'' and assigns it a numeric value of 6. Once again, the type of the variable can be inferred by PowerShell, in this case an ''Int32'' number. In fact, since all types are essentially objects, the type of a variable may be identified at any time by calling the ''GetType()'' method of the object:

<pre>
PS C:\Users\Administrator> $numberofcolors.gettype()

IsPublic IsSerial Name BaseType
-------- -------- ---- --------
True True Int32 System.ValueType
</pre>

Having said that PowerShell is a loosely typed language, it is important to note that the data type may be explicitly declared if desired. For example:

<pre>
$numberofcolors = [int32] 6
</pre>

Once a variable has been created, the value assigned to that variable can be changed at any time using the same assignment operator approach:

<pre>
$numberOfShapes = 6 # Set initial values
$myShape = "Circle";

$numberOfShapes = 7; # Change the initial values to new values
$myShape = "Square"
</pre>

== Accessing PowerShell Variable Values ==

Now that we have learned how to create a variable and assign an initial value to it we now need to look at how to access the value currently assigned to a variable. In practice, accessing a variable is as simple as referencing the name it was given when it was created.

For example, if we want to display the value which we assigned to our ''numberofcolors'' variable we can simply reference it in a command:

<pre>
"The number of colors is $numberofcolors."
</pre>

This will cause the following output to appear in the browser:

<tt>The number of colors is 6.</tt>

Similarly we can display the value of the ''mycolor'' variable:

<pre>
"$mycolor is the current color.";
</pre>

== Changing the Type of a PowerShell Variable ==

As we mentioned at the beginning of this chapter, PowerShell supports a number of different variable types. We will look at these types in detail in the next chapter ([[Windows PowerShell 1.0 Types]]). First we are going to look at changing the type of a variable after it has been created.

As previosuly mentioned, PowerShell is what is termed a ''loosely typed'' language. This contrasts with programming languages such as Java which are ''strongly typed'' languages. The rules of a strongly typed language dictate that once a variable has been declared as a particular type, its type cannot later be changed. In Java, for example, you cannot assign a floating point number to a variable that was initially declared as being a string.

Loosely typed languages such as PowerShell (and JavaScript), on the other hand, allow the variable type to be changed at any point in the life of the variable simply by assigning a value of a different type to it. For example, we can create a variable, assign it an integer value and later change it to a string type by assigning a string to it:

<pre>
$myNumber = 6 # variable is of int32 type

$myNumber = "six" # variable has now changed to string type
</pre>

The process of dynamically changing the type of a variable is sometimes referred to as ''automatic type conversion''.

← Older revision		Revision as of 21:12, 1 February 2016
Line 8:		Line 8:


−	<~~google~~>~~BUY_WPS~~</~~google~~>	+	<htmlet>powershell</htmlet>

@@ Line 38: / Line 38: @@
 Values are assigned to variables using the PowerShell ''assignment operator'', represented by the ''='' sign. To assign a value to a variable therefore, the variable name is placed on the left of the expression, followed by the assignment operator. The value to be assigned is then placed to the right of the assignment operator.
-PowerShell is a loosely typed language. In contract to ''strongly'' typed languages such as C#, C++ or Java this means that the ''type'' of the variable does not need to be specified at creation time. Instead, PowerShell infers the type from the data being assigned. For example, let's begin by assigning the word "Red" to a variable named mycolor:
+PowerShell is a loosely typed language. In contrast to ''strongly'' typed languages such as C#, C++ or Java this means that the ''type'' of the variable does not need to be specified at creation time. Instead, PowerShell infers the type from the data being assigned. For example, let's begin by assigning the word "Red" to a variable named mycolor:
 <pre>
@@ Line 317: / Line 317: @@
 </tr>
 </table>

@@ Line 145: / Line 145: @@
 <tr bgcolor="#e9e9e6">
 <td>
-$home
+$Home
 </td>
 <td>
@@ Line 154: / Line 154: @@
 <tr>
 <td>
-<p>$pshome</p>
+<p>$PSHome</p>
 </td>
 <td>
@@ Line 163: / Line 163: @@
 <tr bgcolor="#e9e9e6">
 <td>
-$args
+$Args
 </td>
 <td>
@@ Line 190: / Line 190: @@
 <tr>
 <td>
-<p>$host</p>
+<p>$Host</p>
 </td>
 <td>
@@ Line 199: / Line 199: @@
 <tr bgcolor="#e9e9e6">
 <td>
-$lastexitcode
+$LastExitCode
 </td>
 <td>
@@ Line 208: / Line 208: @@
 <tr>
 <td>
-<p>$error</p>
+<p>$Error</p>
 </td>
 <td>
-List of all errors since invocation of PowerShell session (up to maximum defined by $maximumerrorcount).
+List of all errors since invocation of PowerShell session (up to maximum defined by $MaximumErrorCount).
 </td>
 </tr>
@@ Line 217: / Line 217: @@
 <tr bgcolor="#e9e9e6">
 <td>
-$maximumerrorcount
+$MaximumErrorCount
 </td>
 <td>
@@ Line 289: / Line 289: @@
 <tr bgcolor="#e9e9e6">
 <td>
-$match
+$Match
 </td>
 <td>
@@ Line 298: / Line 298: @@
 <tr>
 <td>
-$shellid
+$ShellId
 </td>
 <td>

@@ Line 1: / Line 1: @@
-<table border="0" cellspacing="0">
+<table border="0" cellspacing="0" width="100%"><tr>
 <tr>
 <td width="20%">[[Directing and Formatting Windows PowerShell 1.0 Output|Previous]]<td align="center">[[Windows PowerShell 1.0 Essentials|Table of Contents]]<td width="20%" align="right">[[Basic Windows PowerShell 1.0 Types|Next]]</td>
 <tr>

@@ Line 18: / Line 18: @@
 == Naming a Variable in PowerShell ==
-<google>ADSDAQBOX_FLOW</google>
+<htmlet>adsdaqbox_flow</htmlet>
 In PowerShell, all variable names must begin the dollar sign ($). In general any string comprising numbers and letters and pre-fixed with a $ can be used as a variable name, with the exception of pre-defined variable names and $_.

← Older revision		Revision as of 13:36, 14 May 2009
Line 1:		Line 1:
		+	<table border="0" cellspacing="0" width="100%">
		+	<tr>
		+	<td width="20%">[[Directing and Formatting Windows PowerShell 1.0 Output\|Previous]]<td align="center">[[Windows PowerShell 1.0 Essentials\|Table of Contents]]<td width="20%" align="right">[[Basic Windows PowerShell 1.0 Types\|Next]]</td>
		+	<tr>
		+	<td width="20%">Directing and Formatting Windows PowerShell 1.0 Output<td align="center"><td width="20%" align="right">Basic Windows PowerShell 1.0 Types</td>
		+	</table>
		+	<hr>
		+
		+
		+	<google>BUY_WPS</google>
		+
		+
	A large part of writing scripts, and for that matter programming in general, involves the handling and manipulation of data. Data can take many forms, ranging from single characters, words and sentences to integers, floating point numbers and true and false values. In object-based scripting environments such as Windows PowerShell, data can also take the form of an ''object'', a self contained module which is capable of encapsulating any number of data values of numerous different types.		A large part of writing scripts, and for that matter programming in general, involves the handling and manipulation of data. Data can take many forms, ranging from single characters, words and sentences to integers, floating point numbers and true and false values. In object-based scripting environments such as Windows PowerShell, data can also take the form of an ''object'', a self contained module which is capable of encapsulating any number of data values of numerous different types.