TOPIC
about_Arithmetic_Operators
SHORT DESCRIPTION
Describes the operators that perform arithmetic in Windows PowerShell.
LONG DESCRIPTION
Arithmetic operators calculate numeric values. You can use one or
more arithmetic operators to add, subtract, multiply, and divide
values, and to calculate the remainder (modulus) of a division operation.
In addition, the addition operator (+) and multiplication operator (*)
also operate on strings, arrays, and hash tables. The addition operator
concatenates the input. The multiplication operator returns multiple copies
of the input. You can even mix object types in an arithmetic statement.
The method that is used to evaluate the statement is determined by the type
of the leftmost object in the expression.
Windows PowerShell supports the following arithmetic operators:
Operator Description Example
-------- ----------- -------
+ Adds integers; concatenates strings, 6+2
arrays, and hash tables. "file" + "name"
- Subtracts one value from another 6-2
value. (get-date).date - 1
- Makes a number a negative number. -6+2
-4
* Multiplies integers; copies strings 6*2
and arrays the specified number of "w" * 3
times.
/ Divides two values. 6/2
% Returns the remainder of a division 7%2
operation.
OPERATOR PRECEDENCE
Windows PowerShell processes arithmetic operators in the following order:
Parentheses ()
- (for a negative number)
*, /, %
+, - (for subtraction)
Windows PowerShell processes the expressions from left to right according
to the precedence rules. The following examples show the effect of the
precedence rules:
C:\PS> 3+6/3*4
11
C:\PS> 10+4/2
12
C:\PS> (10+4)/2
7
C:\PS> (3+3)/ (1+1)
3
The order in which Windows PowerShell evaluates expressions might differ
from other programming and scripting languages that you have used. The
following example shows a complicated assignment statement.
C:\PS> $a = 0
C:\PS> $b = 1,2
C:\PS> $c = -1,-2
C:\PS> $b[$a] = $c[$a++]
C:\PS> $b
1
-1
In this example, the expression $a++ is evaluated before $c[$a++].
Evaluating $a++ changes the value of $a. The variable $a in $b[$a]
equals 1, not 0, so the statement assigns a value to $b[1], not $b[0].
ADDING AND MULTIPLYING NON-NUMERIC TYPES
You can add numbers, strings, arrays, and hash tables. And, you can
multiply numbers, strings, and arrays. However, you cannot multiply hash
tables.
When you add strings, arrays, or hash tables, the elements are
concatenated. When you concatenate collections, such as arrays or hash
tables, a new object is created that contains the objects from both
collections. If you try to concatenate hash tables that have the same key,
the operation fails.
For example, the following commands create two arrays and then add them:
C:\PS> $a = 1,2,3
C:\PS> $b = "A","B","C"
C:\PS> $a + $b
1
2
3
A
B
C
You can also perform arithmetic operations on objects of different types.
The operation that Windows PowerShell performs is determined by the
Microsoft .NET Framework type of the leftmost object in the operation.
Windows PowerShell tries to convert all the objects in the operation to the
.NET Framework type of the first
object. If it succeeds in converting the objects, it performs the operation
appropriate to the .NET Framework type of the first object. If it fails to
convert any of the objects, the operation fails.
The following example demonstrates the use of the addition and
multiplication operators in operations that include different object types:
C:\PS> "file" + 16
file16
C:\PS> $array = 1,2,3
C:\PS> $array + 16
1
2
3
16
C:\PS> $array + "file"
1
2
3
file
C:\PS> "file" * 3
filefilefile
Because the method that is used to evaluate statements is determined by the
leftmost object, addition and multiplication in Windows PowerShell are not
strictly commutative. For example, (a + b) does not always equal (b + a),
and (a * b) does not always equal (b * a).
The following examples demonstrate this principle:
C:\PS> "file" + 2
file2
C:\PS> 2 + "file"
Cannot convert value "file" to type "System.Int32". Error: "Input
string was not in a correct format."
At line:1 char:4
+ 2 + <<<< "file"
C:\PS> "file" * 3
filefilefile
C:\PS> 3 * "file"
Cannot convert value "file" to type "System.Int32". Error: "Input
string was not in a correct format."
At line:1 char:4
+ 3 * <<<< "file"
Hash tables are a slightly different case. You can add hash tables. And,
you can add a hash table to an array. However, you cannot add any other
type to a hash table.
The following examples show how to add hash tables to each other and to
other objects:
C:\PS> $hash1 = @{a=1; b=2; c=3}
C:\PS> $hash2 = @{c1="Server01"; c2="Server02"}
C:\PS> $hash1 + $hash2
Name Value
---- -----
c2 Server02
a 1
b 2
c1 Server01
c 3
C:\PS> $hash1 + 2
You can add another hash table only to a hash table.
At line:1 char:9
+ $hash1 + <<<< 2
C:\PS> 2 + $hash1
Cannot convert "System.Collections.Hashtable" to "System.Int32".
At line:1 char:4
+ 2 + <<<< $hash1
The following examples demonstrate that you can add a hash table to an
array. The entire hash table is added to the array as a single object.
C:\PS> $array = 1,2,3
C:\PS> $array + $hash1
1
2
3
Name Value
---- -----
a 1
b 2
c 3
C:\PS> $sum = $array + $hash1
C:\PS> $sum.count
4
C:\PS> $sum[3]
Name Value
---- -----
a 1
b 2
c 3
PS C:\ps-test> $sum + $hash2
1
2
3
Name Value
---- -----
a 1
b 2
c 3
c2 Server02
The following example shows that you cannot add hash tables that contain
the same key:
C:\PS> $hash1 = @{a=1; b=2; c=3}
C:\PS> $hash2 = @{c="red"}
C:\PS> $hash1 + $hash2
Bad argument to operator '+': Item has already been added.
Key in dictionary: 'c' Key being added: 'c'.
At line:1 char:9
+ $hash1 + <<<< $hash2
Although the addition operators are very useful, use the assignment
operators to add elements to hash tables and arrays. For more information
see about_assignment_operators. The following examples use the +=
assignment operator to add items to an array:
C:\PS> $array
1
2
3
C:\PS> $array + "file"
1
2
3
file
C:\PS> $array
1
2
3
C:\PS> $array += "file"
C:\PS> $array
1
2
3
file
C:\PS> $hash1
Name Value
---- -----
a 1
b 2
c 3
C:\PS> $hash1 += @{e = 5}
C:\PS> $hash1
Name Value
---- -----
a 1
b 2
e 5
c 3
Windows PowerShell automatically selects the .NET Framework numeric type
that best expresses the result without losing precision. For example:
C:\PS> 2 + 3.1
5.1
C:\PS> (2). GetType().FullName
System.Int32
C:\PS> (2 + 3.1).GetType().FullName
System.Double
If the result of an operation is too large for the type, the type of the
result is widened to accommodate the result, as in the following example:
C:\PS> (512MB).GetType().FullName
System.Int32
C:\PS> (512MB * 512MB).GetType().FullName
System.Double
The type of the result will not necessarily be the same as one of the
operands. In the following example, the negative value cannot be cast to an
unsigned integer, and the unsigned integer is too large to be cast to
Int32:
C:\PS> ([int32]::minvalue + [uint32]::maxvalue).gettype().fullname
System.Int64
In this example, Int64 can accommodate both types.
The System.Decimal type is an exception. If either operand has the Decimal
type, the result will be of the Decimal type. If the result is too large
for the Decimal type, it will not be cast to Double. Instead, an error
results.
C:\PS> [Decimal]::maxvalue
79228162514264337593543950335
C:\PS> [Decimal]::maxvalue + 1
Value was either too large or too small for a Decimal.
At line:1 char:22
+ [Decimal]::maxvalue + <<<< 1
ARITHMETIC OPERATORS AND VARIABLES
You can also use arithmetic operators with variables. The operators act on
the values of the variables. The following examples demonstrate the use of
arithmetic operators with variables:
C:\PS> $intA = 6
C:\PS> $intB = 4
C:\PS> $intA + $intB
10
C:\PS> $a = "Windows "
C:\PS> $b = "PowerShell "
C:\PS> $c = 2
C:\PS> $a + $b + $c
Windows PowerShell 2
ARITHMETIC OPERATORS AND COMMANDS
Typically, you use the arithmetic operators in expressions with numbers,
strings, and arrays. However, you can also use arithmetic operators with
the objects that commands return and with the properties of those objects.
The following examples show how to use the arithmetic operators in
expressions with Windows PowerShell commands:
C:\PS> get-date
Wednesday, January 02, 2008 1:28:42 PM
C:\PS> $day = new-timespan -day 1
C:\PS> get-date + $day
Thursday, January 03, 2008 1:34:52 PM
C:\PS> get-process | where {($_.ws * 2) -gt 50mb}
Handles NPM(K) PM(K) WS(K) VM(M) CPU(s) Id ProcessName
------- ------ ----- ----- ----- ------ -- -----------
1896 39 50968 30620 264 1,572.55 1104 explorer
12802 78 188468 81032 753 3,676.39 5676 OUTLOOK
660 9 36168 26956 143 12.20 988 powershell
561 14 6592 28144 110 1,010.09 496 services
3476 80 34664 26092 234 ...45.69 876 svchost
967 30 58804 59496 416 930.97 2508 WINWORD
EXAMPLES
The following examples show how to use the arithmetic operators in
Windows PowerShell:
C:\PS> 1 + 1
2
C:\PS> 1 - 1
0
C:\PS> -(6 + 3)
-9
C:\PS> 6 * 2
12
C:\PS> 7 / 2
3.5
C:\PS> 7 % 2
1
C:\PS> w * 3
www
C:\PS> 3 * "w"
Cannot convert value "w" to type "System.Int32". Error: "Input string was not
in a correct format."
At line:1 char:4
+ 3 * <<<< "w"
PS C:\ps-test> "Windows" + " " + "PowerShell"
Windows PowerShell
PS C:\ps-test> $a = "Windows" + " " + "PowerShell"
PS C:\ps-test> $a
Windows PowerShell
C:\PS> $a[0]
W
C:\PS> $a = "TestFiles.txt"
C:\PS> $b = "C:\Logs\"
C:\PS> $b + $a
C:\Logs\TestFiles.txt
C:\PS> $a = 1,2,3
C:\PS> $a + 4
1
2
3
4
C:\PS> $servers = @{0 = "LocalHost"; 1 = "Server01"; 2 = "Server02"}
C:\PS> $servers + @{3 = "Server03"}
Name Value
---- -----
3 Server03
2 Server02
1 Server01
0 LocalHost
C:\PS> $servers
Name Value
---- -----
2 Server02
1 Server01
0 LocalHost
C:\PS> $servers += @{3 = "Server03"} #Use assignment operator
C:\PS> $servers
Name Value
---- -----
3 Server03
2 Server02
1 Server01
0 LocalHost
SEE ALSO
about_arrays
about_assignment_operators
about_comparison_operators
about_hash_tables
about_operators
about_variables
Get-Date
New-TimeSpan
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