What is the logic behind flags and methods? - powershell

Question

For example:
> "a,b,c" -split ","
a
b
c
> "a,b,c".split(",")
a
b
c
> "a,b,c".length
5
> "a,b,c" -length
At line:1 char:9
+ "a,b,c" -length
+ ~~~~~~~
Unexpected token '-length' in expression or statement.
+ CategoryInfo : ParserError: (:) [], ParentContainsErrorRecordException
+ FullyQualifiedErrorId : UnexpectedToken
So not every method can be expressed as an flag/argument list. I'm not even sure that .split and -split are the same thing or whether this is by chance.
When should I expect to use a flag and when a method? How do I discover all flags available (for a string, a number, etc.
Another thing is that ls -? returns a help text, but "foo" -? doesn't. So while it accepts flags, it is not really treated as a command

Answer 1

It boils down to this.
This ... "a,b,c" -length
About Operators
An operator is a language element that you can use in a command or expression.
https://learn.microsoft.com/en-us/powershell/module/microsoft.powershell.core/about/about_operators?view=powershell-5.1
Because there are several operator types, the above is not a single source doc reference.
Vs this... "a,b,c".length
About methods
Describes how to use methods to perform actions on objects in PowerShell.
Methods allow you to examine, compare and format many properties of a PowerShell Object, perform an action.
https://learn.microsoft.com/en-us/powershell/module/microsoft.powershell.core/about/about_methods?view=powershell-5.1
From your example :
String.Split Method
Returns a string array that contains the substrings in this instance that are delimited by elements of a specified string or Unicode character array
https://msdn.microsoft.com/en-us/library/system.string.split(v=vs.110).aspx
About Split
The Split operator splits one or more strings into substrings.
https://learn.microsoft.com/en-us/powershell/module/microsoft.powershell.core/about/about_split?view=powershell-5.1
String.Length Property
The Length property returns the number of Char objects in this instance, not the number of Unicode characters.
You'll note if you open this in the PowerShell_ISE.exe or VSCode, you'll see right away, the item 4 is immediately shown as an syntax error even before you run. This is denoted by the red squiggle. That marker means it will never work, so no real reason to try it.
Just because you can type it, does not make it right. If you type a '-' after a space for anything you get a list of what is expected. Well, if you are in the PowerShel_ISE or Visual Studio Code. If you are in the PowerShell console host, you have to hit the tab key to tab through the list or use CRTL + Spacebar to see the full list, then tab or arrow to what you want to use.
('a,b,c').length # this is an array, and this is returning the count of the elements in the array
5
('a,b,c','d,e,f').length # note the element count difference
2
('a,b,c').Length # property use of a .Net class
5
('a,b,c') -length # attempted unknown / invalid switch (PowerShell operator)
To know what you can and cannot do to an object or how, you have to what it supports. That is what Get-Member is for.
So the Array allows this..
('a,b,c') | Get-Member
and this..
('abc') | Get-Member
Most common listed
Name MemberType Definition
---- ---------- ----------
...
Split Method string[] Split(Params char[] separator), string[] Split(char[] separator, int count), string[] Sp...
...
Substring Method string Substring(int startIndex), string Substring(int startIndex, int length)
...
ToLower Method string ToLower(), string ToLower(cultureinfo culture)
...
ToString Method string ToString(), string ToString(System.IFormatProvider provider), string IConvertible.ToString...
...
ToUpper Method string ToUpper(), string ToUpper(cultureinfo culture)
...
Trim Method string Trim(Params char[] trimChars), string Trim()
TrimEnd Method string TrimEnd(Params char[] trimChars)
TrimStart Method string TrimStart(Params char[] trimChars)
Chars ParameterizedProperty char Chars(int index) {get;}
Length Property int Length {get;}
As for this...
When should I expect to use a flag and when a method?
How do I discover all flags available (for a string, a number, etc.
You have to read the help file on the cmdlet you are trying to use, or at minimum it's examples.
Get-Help -Name Get-ItemProperty -Full
Get-Help -Name Get-ItemProperty -Examples
Then info on the cmdlet / function you are trying to use
(Get-Command -Name Get-ItemProperty).Parameters
switches (flags) which will expect a value to the right of it or not, see the property values line below
Then what you can use the cmdlet/function on.
Get-ItemProperty -Path D:\Temp | Format-Table -AutoSize -Wrap
Get-ItemProperty -Path D:\Temp | Format-List
Get-ItemProperty -Path D:\Temp | Format-List -Force
Get-ItemProperty -Path D:\Temp | Select-Object -Property * # property values
(Get-ItemProperty -Path D:\Temp) | Get-Member
As for this...
Another thing is that ls -? returns a help text, but "foo" -? doesn't.
So while it accepts flags, it is not really treated as a command
Foo is not a valid name of anything in PowerShell, unless you created a foo function or module. So, it should hot return anything.
Again, just because you can type it, does not make it correct.
In most cases, if you are doing the above and you do not get automatic intellisense, then what you are doing is probably wrong.
To see all the cmdlets, functions, etc you have on your system for use. You do this.
Get-Command