Microsoft PowerShell's Syntax
Introduction to PowerShell's Syntax
The fact that you almost don't need this page is a testament to the intuitive nature of PowerShell. Yet for those who wish to save time fumbling with the PowerShell syntax, it may pay to have a refresher of these rules of scripting grammar.
Topics for PowerShell Syntax
- Case Insensitive
- Comma and Semi-colon
- Hyphen -dash -minus
- Pipeline, the Pipe Symbol | or (¦)
- Brackets () {} []
- Double and Single Quotes
- + Plus as a Concatenator
- Switch
- Operators
♣
Case Insensitive
PowerShell is fundamentally case insensitive. Every object and every cmdlet is case insensitive. Set-Location performs exactly the same action as set-location. However, where your data has case sensitive values, there are PowerShell operators to deal with 'case'. For example, -gt means greater than, -match means contains a particular string value. Now you can force these and similar operators to be case sensitive by prefixing with a 'c'. -cmatch, or -cgt mean that the comparison will be case sensitive.
Comma and Semi-colon
For many years a bad attitude to syntax hindered me. My breakthrough was realizing that punctuation marks are there to aid the readers' understanding; my mistake was thinking syntax rules were designed by my English teacher as a way of finding new ways to tell me off.
With PowerShell's syntax the comma is frequently used to separate items on a list. Whereas the semi-colon is to split separate ideas. Let us study this example:
Clear-host
$i=0
$Log = get-EventLog -list
ForEach ($Item in
$Log) {
"{0,-30} {1,-20} {2,13}" -f `
$Item.Log, $Item.OverflowAction,
$Item.MaximumKilobytes
}
Note 1: Each $Item is separated by a comma. No sign of the semi-colon, yet.
Note 2: The comma is also used so separate items in an array {0,-30}
Suppose we want to count the number of eventlogs. Let us introduce a variable $i
Clear-host
$i=0
$Log = get-EventLog -list
ForEach ($Item in
$Log) {
"{0,-30} {1,-20} {2,13}" -f `
$Item.Log, $Item.OverflowAction,
$Item.MaximumKilobytes; $i++
}
"There are $i eventlogs"
Note 1: The counter variable, $i++ is new element, which is not connected to the list; time for a semi-colon before the counter variable.
= Equals and ! Not equal
The equals sign (=) behaves just as expected. As usual, '=' tests for equivalence, or sets a variable to be equal to a certain value. The equals sign has a counterpart ! (Exclamation mark) meaning, 'not equal'. You may also employ -not instead of ! I just include these two basic operators, '=' and ! for completeness.
Hyphen -dash -minus
Some people call this symbol (-) minus, others a refer to this sign as a dash, I mostly call it a hyphen. Let me be clear, this character maps to ASCII 45, to see the character, hold down ALT key, type 45 on numeric keypad, now let go of ALT key.
PowerShell uses this - symbol for two purposes. Firstly, to join verb-Noun pairs, for example out-File guy.txt. Secondly, this minus sign is also used for parameters, modifiers, or filters such as -list; as in get-Eventlog -list. The trap I fall into is to put a space between the minus and the modifier. get -eventlog is clearly wrong, because there is a space between get and -. The correct format is, get-Eventlog, with no space.
Pipeline, the Pipe Symbol | (Sometimes looks like ¦)
The ability to pipe the output of one command, so that it becomes the input of the second command is PowerShell's signature tune. Thus it is important to be clear about this | symbol.
When typed in notepad, the pipeline symbol looks like this: | but when typed in the Microsoft Shell it looks like ¦. On my keyboard the key I am using this symbol is next to the z, however I have seen keyboards where the pipeline key is next to numeric 1 on the top row. Once you find, then type the key, you get a pipe symbol (|).
To be crystal clear this pipeline symbol corresponds to ASCII 124. N.B this not ASCI 0166. Test by holding down the Alt key and typing the number (124 or 0166) on the numeric pad, then letting go of the Alt key.
In PowerShell syntax the pipeline symbol (|) has three roles.
- Think of the pipeline as a method for joining two commands.
get-Eventlog system | format-list
You could even have two pipelines in one statement. - PowerShell deploys Pipeline to introduce 'Where' clause.
get-Eventlog security |where {$_.Eventid -eq "540"} -
Pipeline is similar to 'more' in DOS
get-Eventlog system | more
Guy Recommends: SolarWinds Engineer's Toolset v10
The Engineer's Toolset v10 provides a comprehensive console of utilities for troubleshooting computer problems. Guy says it helps me monitor what's occurring on the network, and the tools teaches me more about how the system literally operates.
There are so many good gadgets, it's like having free rein of a sweetshop. Thankfully the utilities are displayed logically: monitoring, discovery, diagnostic, and Cisco tools. Download your copy of the Engineer's Toolset v 10
PowerShell's Brackets
PowerShell's brackets surprised me. Each type has a specific role, the wrong bracket will cause an otherwise sound command, to fail miserably. The message is clear, you have to understand your brackets. Each of these (), {} or [] has a different purpose. After a while, PowerShell's syntax becomes your friend in producing error-free code. For instance, if you need a script block, always associate the task with the {Braces style of bracket}.
1) () Parenthesis or Curved brackets are used for required options in the foreach loop
Example: $disk= WmiObject Win32_LogicalDisk
"Drive Letter Size GB "
foreach
($drive in $disk ) {"Drive = " + $drive.Name}
2) {} Braces or 'curly' brackets are required for block expressions within a command, for instance, the 'where' or 'where-object' command.
Example: get-service | where {$_.status -eq "stopped" }
3) [] Square brackets are used for optional elements, for example, to filter services beginning with 's':
Example: get-service [s]*
I have also found square brackets are needed for math functions such as [int]value
Example: [int]TotalProcessorTime
4) > and >> work as with DOS and cmd, they output the results of your commands not to screen, but to a text file. The double chevron >> appends, the single > will overwrite any existing data in the file.
Conclusion, the type of bracket really matters, therefore always double check before you select {} () or [].
Double and Single Quotes
As with brackets, the type of quotation mark is highly significant in PowerShell syntax. Here is an example to illustrate the differences between single quotes and double quotes in PowerShell
$Bill = 57
$Tax = 7
$Total = $Bill + $Tax
"My total is $Total"
Using the double quotes illustrates PowerShell's intelligence, it
realizes that $Total is variable holding the value 64, thus the output is:
My total is 64
However, if we substitute single quotes: 'My total is $Total', we get a different, literal answer: My total is $Total. PowerShell assumed that for a reason best known to us, we did not want it to use the math representation.
+ Plus as a Concatenator
When I wanted to join text and numbers, I spent time looking for PowerShell's concatenator. Silly me, all
I need is the simple + plus sign. This is because in PowerShell +
joins text strings as well as its traditional job of adding numbers. For example:
"My total is " + $Total
Achieve Word-wrap with
Backtick` 
While word-wrap is neither essential, nor strictly speaking a syntactic element, it makes scripts easier to read. The problem with most scripting languages, including PowerShell, is that an end-of-line means end of command.
A new line, means a new command.
Thus we need a special symbol to control word-wrap. PowerShell employs the backtick `. I have seen this same character referred to as a grave. A sure way of typing this key is to hold down the Alt key. Now type 0096 on the numeric pad, let go of the Alt key.
Guy
Recommends: A Free tool from SolarWinds: Config Generator
Config Generator (CG) is a free tool, which puts you in charge of controlling changes to network routers and other SNMP devices. Boost your network performance by activating network device features you've already paid for.
Guy says that for newbies the biggest benefit of this free tool is that it will provide the impetus for you to learn more about configuring the SNMP service with its 'Traps' and 'Communities'. This is a brand new free utility which Solarwinds released on January 26th 2010.
Download your free copy of the Config Generator
PowerShell's Switch Command
In VBScript one of my favourite techniques was Select Case, here in PowerShell the equivalent technique is called 'Switch'. Here is an example. Guess the outcome?
$Choice = 2
switch ($Choice)
{
1 {"First
Choice"}
2 {"Second Choice"}
3 {"Third Choice"}
}
The answer is determined by the value of $Choice, in this instance 2, therefore the result would be 2 "Second Choice"
PowerShell's Operators
| Operator |
Definition |
| # | # The hash key is for comments |
| + | Add |
| - | Subtract |
| * | Multiply |
| / | Divide |
| % | Modulus (Some call it Modulo) - Means remainder 17 % 5 = 2 Remainder |
| = | equal |
| -not | logical not equal |
| ! | logical not equal |
| -band | binary and |
| -bor | binary or |
| -bnot | binary not |
| -replace | Replace (e.g. "abcde" –replace "b","B") (case insensitive) |
| -ireplace | Case-insensitive replace (e.g. "abcde" –ireplace "B","3") |
| -creplace | Case-sensitive replace (e.g. "abcde" –creplace "B","3") |
| -and | AND (e.g. ($a -ge 5 -AND $a -le 15) ) |
| -or | OR (e.g. ($a –eq "A" –OR $a –eq "B") ) |
| -is | IS type (e.g. $a -is [int] ) |
| -isnot | IS not type (e.g. $a -isnot [int] ) |
| -as | convert to type (e.g. 1 -as [string] treats 1 as a string ) |
| .. | Range operator (e.g. foreach ($i in 1..10) {$i } ) |
| & | call operator (e.g. $a = "Get-ChildItem" &$a executes Get-ChildItem) |
| . (dot followed by a space) | call operator (e.g. $a = "Get-ChildItem" . $a executes Get-ChildItem in the current scope) |
| . |
.Period or .full stop for an objects properties $CompSys.TotalPhysicalMemory |
| -F | Format operator (e.g. foreach ($p in Get-Process) { "{0,-15} has {1,6} handles" –F $p.processname,$p.Handlecount } ) |
PowerShell's Conditional or Comparison Operators
| Operator |
Definition |
| -lt | Less than |
| -le | Less than or equal to |
| -gt | Greater than |
| -ge | Greater than or equal to |
| -eq | Equal to |
| -ne | Not Equal to |
| -contains |
Determine elements in a group. This always returns Boolean $True or $False. |
| -notcontains |
Determine excluded elements in a group This always returns Boolean $True or $False. |
| -like | Like - uses wildcards for pattern matching |
| -notlike | Not Like - uses wildcards for pattern matching |
| -match | Match - uses regular expressions for pattern matching |
| -notmatch | Not Match - uses regular expressions for pattern matching |
| Bitwise | |
| -band | Bitwise AND |
| -bor | Bitwise OR |
| -is | Is of Type |
| -isnot | Is not of Type |
| Other Operators | |
| if(condition) | If condition |
| elseIf(condition) | ElseIF |
| else(condition) | Else |
| > |
Redirect, for example, output to text file Example .\cmdlet > stuff.txt |
| >> | Same as Redirect except it appends to an existing file |
Summary of Microsoft PowerShell Syntax
Every language must have its grammar rules. However, with PowerShell syntax the rules for brackets, quotation marks and commas, all seem logical and straightforward.
See more PowerShell examples for syntax advice
• PowerShell Home • Syntax • -f format • Pipeline • Quotes • Format-table • Group • Select-String
Please write in if you see errors of any kind. Please report any factual mistakes, grammatical errors or broken links, I will be happy to not only to correct the fault, but also to give you credit.
Download my ebook:
|
*
|
|
|
|
Home Copyright © 1999-2010 Computer Performance LTD All rights reserved Please report a broken link, or an error. | |
