| Server IP : 134.29.175.74 / Your IP : 216.73.216.160 Web Server : nginx/1.10.2 System : Windows NT CST-WEBSERVER 10.0 build 19045 (Windows 10) i586 User : Administrator ( 0) PHP Version : 7.1.0 Disable Function : NONE MySQL : OFF | cURL : ON | WGET : OFF | Perl : OFF | Python : OFF | Sudo : OFF | Pkexec : OFF Directory : /Windows/System32/WindowsPowerShell/v1.0/en-US/ |
Upload File : |
ABOUT SWITCH
Short description
Explains how to use a switch to handle multiple If statements.
Long description
To check a condition in a script or function, use an If statement. The If
statement can check many types of conditions, including the value of
variables and the properties of objects.
To check multiple conditions, use a Switch statement. The Switch statement
is equivalent to a series of If statements, but it is simpler. The Switch
statement lists each condition and an optional action. If a condition
obtains, the action is performed.
The Switch statement can use the $_ and $switch automatic variables. For
more information, see about_Automatic_Variables.
A basic Switch statement has the following format:
Switch (<test-value>)
{
<condition> {<action>}
<condition> {<action>}
}
For example, the following Switch statement compares the test value, 3, to
each of the conditions. When the test value matches the condition, the
action is performed.
switch (3)
{
1 {"It is one."}
2 {"It is two."}
3 {"It is three."}
4 {"It is four."}
}
It is three.
In this simple example, the value is compared to each condition in the
list, even though there is a match for the value 3. The following Switch
statement has two conditions for a value of 3. It demonstrates that, by
default, all conditions are tested.
switch (3)
{
1 {"It is one."}
2 {"It is two."}
3 {"It is three."}
4 {"It is four."}
3 {"Three again."}
}
It is three.
Three again.
To direct the Switch to stop comparing after a match, use the Break
statement. The Break statement terminates the Switch statement.
switch (3)
{
1 {"It is one."}
2 {"It is two."}
3 {"It is three."; Break}
4 {"It is four."}
3 {"Three again."}
}
It is three.
If the test value is a collection, such as an array, each item in the
collection is evaluated in the order in which it appears. The following
examples evaluates 4 and then 2.
switch (4, 2)
{
1 {"It is one." }
2 {"It is two." }
3 {"It is three." }
4 {"It is four." }
3 {"Three again."}
}
It is four.
It is two.
Any Break statements apply to the collection, not to each value, as shown
in the following example. The Switch statement is terminated by the Break
statement in the condition of value 4.
switch (4, 2)
{
1 {"It is one."; Break}
2 {"It is two." ; Break }
3 {"It is three." ; Break }
4 {"It is four." ; Break }
3 {"Three again."}
}
It is four.
Syntax
The complete Switch statement syntax is as follows:
switch [-regex|-wildcard|-exact][-casesensitive] (<value>)
{
"string"|number|variable|{ expression } { statementlist }
default { statementlist }
}
or
switch [-regex|-wildcard|-exact][-casesensitive] -file filename
{
"string"|number|variable|{ expression } { statementlist }
default { statementlist }
}
If no parameters are used, Switch behaves the same as using the EXACT
parameter. It performs a case-insensitive match for the value. If the value
is a collection, each element is evaluated in the order in which it
appears.
The Switch statement must include at least one condition statement.
The Default clause is triggered when the value does not match any of the
conditions. It is equivalent to an Else clause in an If statement. Only one
Default clause is permitted in each Switch statement.
Switch has the following parameters:
- WILDCARD - Indicates that the condition is a wildcard string. If the
match clause is not a string, the parameter is ignored. The comparison
is case-insensitive.
- EXACT - Indicates that the match clause, if it is a string, must match
exactly. If the match clause is not a string, this parameter is
ignored. The comparison is case-insensitive.
- CASESENSITIVE - Performs a case-sensitive match. If the match clause is
not a string, this parameter is ignored.
- FILE- Takes input from a file rather than a value statement. If
multiple FILE parameters are included, only the last one is used. Each
line of the file is read and evaluated by the Switch statement. The
comparison is case-insensitive.
- REGEX - Performs regular expression matching of the value to the
condition. If the match clause is not a string, this parameter is
ignored. The comparison is case-insensitive. The $matches automatic
variable is available for use within the matching statement block.
[!NOTE] When specifying conflicting values, like REGEX and WILDCARD, the
last parameter specified takes precedence, and all conflicting parameters
are ignored. Multiple instances of parameters are also permitted.
However, only the last parameter used is effective.
In this example, an object that's not a string or numerical data is passed
to the Switch. The Switch performs a string coercion on the object and
evaluates the outcome.
$test = @{
Test = 'test'
Test2 = 'test2'
}
$test.ToString()
switch -Exact ($test)
{
'System.Collections.Hashtable'
{
'Hashtable string coercion'
}
'test'
{
'Hashtable value'
}
}
System.Collections.Hashtable
Hashtable string coercion
In this example, there is no matching case so there is no output.
switch ("fourteen")
{
1 {"It is one."; Break}
2 {"It is two."; Break}
3 {"It is three."; Break}
4 {"It is four."; Break}
"fo*" {"That's too many."}
}
By adding the Default clause, you can perform an action when no other
conditions succeed.
switch ("fourteen")
{
1 {"It is one."; Break}
2 {"It is two."; Break}
3 {"It is three."; Break}
4 {"It is four."; Break}
"fo*" {"That's too many."}
Default {
"No matches"
}
}
No matches
For the word "fourteen" to match a case you must use the -Wildcard or
-Regex parameter.
PS> switch -Wildcard ("fourteen")
{
1 {"It is one."; Break}
2 {"It is two."; Break}
3 {"It is three."; Break}
4 {"It is four."; Break}
"fo*" {"That's too many."}
}
That's too many.
The following example uses the -Regex parameter.
$target = 'https://bing.com'
switch -Regex ($target)
{
'^ftp\://.*$' { "$_ is an ftp address"; Break }
'^\w+@\w+\.com|edu|org$' { "$_ is an email address"; Break }
'^(http[s]?)\://.*$' { "$_ is a web address that uses $($matches[1])"; Break }
}
https://bing.com is a web address that uses https
A Switch statement condition may be either:
- An expression whose value is compared to the input value
- A script block which should return $true if a condition is met.
The $_ automatic variable contains the value passed to the switch statement
and is available for evaluation and use within the scope of the condition
statements.
The action for each condition is independent of the actions in other
conditions.
The following example demonstrates the use of script blocks as Switch
statement conditions.
switch ("Test")
{
{$_ -is [String]} {
"Found a string"
}
"Test" {
"This $_ executes as well"
}
}
Found a string
This Test executes as well
If the value matches multiple conditions, the action for each condition is
executed. To change this behavior, use the Break or Continue keywords.
The Break keyword stops processing and exits the Switch statement.
The Continue keyword stops processing the current value, but continues
processing any subsequent values.
The following example processes an array of numbers and displays if they
are odd or even. Negative numbers are skipped with the Continue keyword. If
a non-number is encountered, execution is terminated with the Break
keyword.
switch (1,4,-1,3,"Hello",2,1)
{
{$_ -lt 0} { Continue }
{$_ -isnot [Int32]} { Break }
{$_ % 2} {
"$_ is Odd"
}
{-not ($_ % 2)} {
"$_ is Even"
}
}
1 is Odd
4 is Even
3 is Odd
See also
about_Break
about_Continue
about_If
about_Script_Blocks