Arul Kumaravel's WebLog

Arithmetic Operators (also see Unary and String operators)

Array Comparison

Return all elements equal to 3:

1,2,3,5,3,2 –eq 3

Return all elements less than 3:

1,2,3,5,3,2 –lt 3

Test if 2 exists:

if (1, 3, 5 –eq 2) …

Other operators:  -gt, -le, -ge

Arrays

* Arrays are zero-based.

Assignment Operators

Associative Arrays (Hashtables)

Boolean Values

break (scripting)

The "break" commands exits a loop.  Example:

while (1)

{

            $a = something

            if ($a –eq 1) break;

}

Command Expansion Operators

Comments

# This is a comment.

$a = "#This is not a comment…"

$a = "something" # …but this is.

Comparison Operators

continue (scripting)

The continue statement continues the next iteration of a loop without breaking out of it.  Example:

while (1)

{

            $a = something

            if ($a –eq 1) (continue)

            # This line is not reached unless $a == 1

}

#  This line is never reached.

Dot Sourcing

Dot sourcing allows running functions, script blocks, and scripts in the current scope rather than a local one.  Example:

. MyFunction

If MyFunction sets a variable, it is set in the current scope rather than the function’s local scope.

Escape Character and Escape Sequences

The MSH escape character is the backwards apostrophe, or `.  To make a character literal, precede it with `.  To specify a ` use ``.

Execution Order

MSH attempts to resolve commands in the following order:  aliases, functions, cmdlets, scripts, executables, normal files

for (scripting)

[:label] for ([initializer]; [condition]; [iterator]) {}

Example:

for ($i = 0; $i –lt 5; %i++) {write-object $i}

foreach (scripting)

[:label] foreach (identifier in pipeline or collection) {}

Example:

$i = 1,2,3

foreach ($z in $i) {write-object $z}

functions (scripting)

function MyFunction {

            write-object $args[0]

}

Filters (scripting)

filter MyFilter {

            $_.name

}

if/elseif/else (scripting)

if (condition) {…}

elseif (condition) {…}

else {…}

On the command-line, the closing brace must be on the same line as elseif and else.  This restriction does not exist for scripts

Invoke Operator

The & operator can be used to invoke the contents of an object.  Example:

$a = "get-process"

&$a

$a = { get-process | pick-head 2 }

&$a

Logical Operators

Method Calls

Methods can be called on objects.  Examples:

$a = "This is a string"

$a.ToUpper()

$a.SubString(0,3)

$a.SubString(0,($a.length/2))

$a.Substring(($a.length/2), ($a.length/3))

Static methods may be called as well:

[string].format("{0} {1} {2}","one",2,(get-date))

MSH Variables

Object Properties

An object’s properties can be referenced directly with the "." operator.

$a = get-date

$a.Date

$a.TimeOfDay.Hours

Operator Precedence

In MSH, operators are evaluated in the following precedence:  () {}, @ $, !, [ ], ., &, ++ --, Unary + -, * / %, Binary + -, Comparison Operators, -and –or, |, > >>, =

Redirection

The > and >> operators redirect command output to files.  The > operator creates a new file or truncates and existing one, while the >> operator appends to an existing file.  Example:

1,2,3 >foo.txt

5,6 >>foo.txt

return (scripting)

The return command exits the current script or function and returns a value.  Example:

function foo {

            ...

}

Script Blocks

Commands and expressions can be stored in a script block object and executed later.  Example:

$block = {get-process; $a=1}

&$block

Scripts

MSH commands can be stored in and executed from script files.  The file extension for MSH scripts is ".msh".  Parameters can be passed to a script and a script can return a value.  Example:

$sum = MyAdder.msh 1 2 3

Strings and String Operators

String constants:

"this is a string, this $variable is expanded"

‘this is a string, this $variable is not expanded’

Examples:

MSH>  "test" + "this"

testthis

MSH>  "{0:M}" -f $(get-date)

June 02

MSH> $a = 1,2,3,4

MSH> $a

1

2

3

4

MSH> $OFS = ":"

MSH> "$a"

1:2:3:4

MSH> "This is a test" -replace "is","IS"

ThIS IS a test

Switch

$a = 3

switch ($a) {

   1 {"got one"}

   2 {"got two"}

   3 {"got three"}

}

$var = "word2"

switch -regex ($var) {

   "word2"  {"Multi-match Exact " + $_ }

   "word.*" {"Multi-match Exact1 " + $_ }

   default  {"Multi-match Default " + $_; break}

   "w.*" {"Previous Break terminated the matching"}

}

$var = "word1","word2","word3"

switch -regex ($var) {

   "word1"  {"Multi-match Exact " + $_ ; continue}

   "word2"  {"Multi-match Exact " + $_ ; continue}

   default  {"Multi-match Default " + $_; continue}

}

Trap

Execute a block of code in a terminating error condition.  Example:

function handler1 { write-host "Hi, I'm a trap handler" }

function handler2 { write-host "Hi, I'm a trap handler2" }

trap [System.Management.Automation.ExecutionFailedException]

{ handler2 ; continue }

trap [System.Management.Automation.ExecutionBreakOnErrorException]

{ handler1 ; continue }

get-content thisisabadfilename -errorp notifystop

set-location thisisabadlocation

Types & Casts

Brackets around a string indicate a type object

Unary Operators

Variables

Format:

$[scope:]name

Examples:

$a = 1

$global:a = 1

$local:a = 1

$env:path = "d:\windows"

            Scope may be either global, local or script

while (scripting)

[:label] while (condition)

{

…

}