Variable expansion in strings and here-strings
PSMDTAG:FAQ: What is the difference between single quoted and double quoted strings? ANSWER: Double quoted string expand variables and single quoted strings do not.
Example:
PS> $x="TEST"
PS> "This is a $x"
This is a TEST
PS> 'This is a $x'
This is a $x
PSMDTAG:FAQ: How do variables expand in strings?
PSMDTAG:FAQ: Why don't properties work with variable expansion in strings?
Variables get expanded in strings not property expressions. Here is an example of a property expression that you might like to use that doesn't work the way you might think it would:
PS> Calc
PS> $c = Get-Process Calc
PS> "Calc uses $c.Handles Handles"
Calc uses System.Diagnostics.Process (calc).Handles Handles
In this example, $c gets expanded to "System.Diagnostics.Process (calc)". The problem is that you wanted the $c.Handles to be expanded.
PSMDTAG:FAQ: How do I expand an expression in a string?
Windows PowerShell will expand a variable or an expression in a string.
Variables look like: $variable
Expressions look like: $(expression)
Thus to get $c.Handles expanded you do the following:
PS> "Calc uses $($c.Handles) Handles"
Calc uses 42 Handles
Now from here, it gets even better. You can put anything put any code you want into that expression. You can put a 40 page script in there if you want. Here is an example:
PS> cat t.ps1
"
Cmds with > 800 handles are: $(
$limit = 800
$procs = Get-Process |where {$_.handles -ge $limit}
foreach ($p in $procs)
{ '`n`t{0}' -f $p.Name.ToUpper()
}
)
"
PS> .\t.ps1
Cmds with > 800 handles are:
CCMEXEC
CSRSS
IEXPLORE
IEXPLORE
LSASS
OUTLOOK
POWERSHELL
PS
SEARCHINDEXER
SVCHOST
SYSTEM
WINLOGON
So by using $(), you can do almost anything you could want to do.
"ALMOST ?!!!??"
Yeah - almost but not really everything. Notice that I used single quotes for the format string in the expression: '`n`t{0}' . The reason I did that is that if I used double quotes, it would have caused a parser error. I could have used escape characters but that wouldn't help me make the point I'm making so ...
PSMDTAG:FAQ: How do I show double quotes within a double quoted string? ANSWER: escape them with a backtick `" or use Here-Strings.
A Here-String is a string which starts with a @" and ends with a "@ (on a line by itself). Here-Strings can use any character you want until it sees a "@ which terminates the string.
PS> cat t.ps1
@"
"Cmds" with > 800 handles are: $(
$limit = 800
$procs = Get-Process |where {$_.handles -ge $limit}
foreach ($p in $procs)
{ "`n`t{0}" -f $p.Name.ToUpper()
}
)
Jeffrey likes to say, "I LOVE HERE-STRINGS"
"@
PS> .\t.ps1
"Cmds" with > 800 handles are:
CCMEXEC
CSRSS
IEXPLORE
IEXPLORE
LSASS
OUTLOOK
POWERSHELL
PS
SEARCHINDEXER
SVCHOST
SYSTEM
WINLOGON
Jeffrey likes to say, "I LOVE HERE-STRINGS"
Here strings are an AWESOME tool for creating HTML or XML documents.
Have a blast!
Jeffrey Snover [MSFT]
Windows PowerShell/Aspen Architect
Visit the Windows PowerShell Team blog at: http://blogs.msdn.com/PowerShell
Visit the Windows PowerShell ScriptCenter at: http://www.microsoft.com/technet/scriptcenter/hubs/msh.mspx
