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enclosure precedence

Essential PowerShell: Know your operator and

enclosure precedence

July 8, 2009Leave a commentGo to comments

PowerShell version 1 comes with a lot of operators, and the list becomes even longer in version 2

with cool new operators like -split and -join. Whether youre writing scripts or using PowerShell interactively, dealing with multiple operators in an expression that possibly contains different

enclosures (brackets, quotation marks, etc.) as well can be very tricky. It is very important to know how the PowerShell interpreter processes the expression so that you can get your expressions right the first time or, if youre not so lucky, so that you can identify the problem in

your expressions later and fix them.

Recently there have been several posts on the forums where the problem has been a lack of

understanding of the operator and enclosure precedence in PowerShell. Thats not too surprising because the precedence order used by the PowerShell interpreter doesnt seem to be documented at this time. You can find the precedence order of arithmetic operators through the

about_arithmetic_operators help file, you can find out some precedence details for specific operators in various operator help files, and you can find out the precedence of command types

through the about_command_precedence help file, but thats about it. There is no single help file that documents the overall operator and enclosure precedence. It doesnt seem to be listed in any of the PowerShell books I have read either.

Fortunately through some ad hoc experimentation and through some reading of the help documentation that does exist it is possible to figure out how all of this works. Ive gone through that exercise recently and the resulting table of operator and enclosure precedence is below.

Before getting to the table though there are a few important things I should mention, as follows:

1. Any items that share the same row in the table have the same precedence and are evaluated

from left to right when adjacent within an expression unless otherwise indicated.2. The intent of this table is to identify a precedence that can be used to create or troubleshoot

more complicated expressions without a lot of guesswork. It is not intended to explain what

each of the operators are and how you can use them (although to help understand expressions you might have to deal with I do mention a few details about some operators

that function differently than the majority of operators in PowerShell).3. If you want to learn about the individual operators and see examples showing how they can

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With that out of the way, here is the operator and enclosure precedence table for PowerShell:

[] Type enclosures Any character placed inside of these enclosures is treated as part of a literal type name. The contents are not

evaluated like an expression would be.

Double-quoted string enclosures

Single-quoted string enclosures

@ @ Double-quoted here-string enclosures

@ @ Single-quoted here-string enclosures

{} Script block enclosures

() Nested expression enclosures

@() Array subexpression enclosures

$() Subexpression enclosures

. Property dereference operator

:: Static member operator

[] Index operator

[int]

[string[]]etc.

Cast operators Multiple adjacent operators in this row

have a right-to-left evaluation.

-split (unary) Split operator (unary)

-join (unary) Join operator (unary)

These operators can be used as unary or

binary operators. Their precedence varies depending on how they are used.

, Comma operator This operator is the array element separator. It can be used as an unary or

binary operator.

++ Increment operator

- - Decrement operator

These unary operators can be used before or after a variable or property. When used before the variable or

property (as a prefix operator), the value is incremented or decremented

first and then the result is passed into the expression in which it is contained. When used after the variable or

property (as a postfix operator), the value is passed into the expression in

which it is contained and then the variable or property is immediately incremented or decremented.

- Negate operator

-not Not operator

! Not operator

-bnot Bitwise not operator

Multiple adjacent operators in this row


.. Range operator

-f Format operator FollowFollow



* Multiplication operator

/ Division operator

% Modulus operator

+ Addition operator

- Subtraction operator

-split

-isplit-csplit

(binary)

Split operator (binary)

-join (binary) Join operator (binary)

-is Type is operator

-isnot Type is not operator

-as Type as operator

-eq

-ieq-ceq

Equal to operator

-ne-ine-cne

Not equal to operator

-gt-igt

-cgt

Greater than operator

-ge-ige

-cge

Greater than or equal to operator

-lt

-ilt-clt

Less than operator

-le

-ile-cle

Less than or equal to operator

-like-ilike-clike

Like operator

-notlike-inotlike-cnotlike

Not like operator

-match-imatch

-cmatch

Match operator

-notmatch-inotmatch

-cnotmatch

Not match operator

-contains

-icontains-ccontains

Contains operator

Does not contain operator

With the exception of the join operator

and the type operators (-is, -isnot, and as), each of the operators in this row

has a case-sensitive and an explicit case-insensitive variant. Case-sensitive variants are prefixed with c (e.g. -ceq)

and case-insensitive variants are prefixed with i (e.g. ireplace).

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-notcontains

-inotcontains-cnotcontains

-replace

-ireplace-creplace

Replace operator

-band Bitwise and operator

-bor Bitwise or operator

-bxor Bitwise exclusive or operator

-and Logical and operator

-or Logical or operator

-xor Logical exclusive or operator

. Dot-sourcing operator

& Call operator

Unary operators that are only valid at the beginning of an expression, a nested expression, or a subexpression.

= Assignment operator

+= Assignment by addition operator

-= Assignment by subtraction operator

*= Assignment by multiplication operator

/= Assignment by division operator

%= Assignment by modulus operator

Multiple adjacent operators in this row


Since this table is created through experimentation and through snippets of information about

precedence that I was able to find in the help files, it may not be entirely accurate. If you find any problems with the precedence information provided here, please let me know and Ill update this table accordingly.

[Update 09-July-2009: Fixed table formatting, added an index operator, added all case-sensitive and case-insensitive variants and adjusted the precedence for the property dereference and static

member operators.]

Thanks,

Kirk out.

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Categories: Essential PowerShell, PowerShell Tags: enclosure precedence, Essential PowerShell,

operator precedence, PoSh, Poshoholic, PowerShellComments (8)Trackbacks (3)Leave a commentTrackback

1.

stejJuly 9, 2009 at 1:58 am | #1

Reply | Quote

Great, I was always wondering, whats the precedence of operators. It is very well defined e.g. for C#, but I havent found anything for PowerShell.

You saved my time!

Kirk MunroJuly 9, 2009 at 1:41 pm | #2Reply | Quote

Thanks for the feedback, Im glad you like it!

2.

Aravind August 19, 2010 at 9:49 pm | #3Reply | Quote

This is very helpful.

3.Jeremy Sproat

January 12, 2011 at 11:02 am | #4Reply | Quote

Theres a subtle gotcha with the bitwise and logical operators.

AND operators should have a higher precedence than OR operators (much like * happens before +). However, in PowerShell v2.0 (and probably v1.0) -band and -bor are evaluated

left to right.

Compare this PowerShell snippet:

PS> 1 -bor 0 -band 00

with Python:

>>> 1 | 0 & 01

When in doubt, use parentheses!

Essential PowerShell: Beware of

promiscuous types

Essential PowerShell: Learn how

to find what you are looking for

whence in PowerShell

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Kirk Munro January 12, 2011 at 11:16 am | #5Reply | Quote

Nice catch, I didnt pick up that one. Youre right about parentheses though, I use them simply because it eliminates the guesswork for someone reading the script later.

Thanks for sharing!

Kirk out.

koenraad April 27, 2011 at 8:03 am | #6

Reply | Quote

The same is true for -and and -orPS> $true -or $true -and $false

FalsePS> $true -or ($true -and $false)

True

4.Sunil

June 19, 2012 at 10:39 pm | #7Reply | Quote

neatly defined. Well done Kirk!

Kirk Munro

June 20, 2012 at 1:43 pm | #8Reply | Quote

Thanks! The details in this post actually made it into PowerShell documentation, so

youll see docs with operator precedence in PowerShell in the next release, plus theyre available online now (http://technet.microsoft.com/en-

us/library/hh847842.aspx).

Kirk out.

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