Addressing comments

1. Clarifying '[]' and null-assigned expressions.
2. Removing "-contains" on switch example from Wouter, it does not appear to be true anymore
3. Adding comments and adjusting some func examples a bit
This commit is contained in:
Andrew Ryan Davis 2020-08-16 21:14:26 -07:00
parent 5c79b4288c
commit e6a53387be

View File

@ -149,25 +149,49 @@ $age = 22
# $null is not an object # $null is not an object
$null # => None $null # => None
# $null, 0, and empty strings and arrays all evaluate to False.
# All other values are True
# $null, 0, and empty strings and arrays all evaluate to False. # $null, 0, and empty strings and arrays all evaluate to False.
# All other values are True # All other values are True
function test ($value) { function test ($value) {
if ($value) {Write-Output 'True'} if ($value) {
else {Write-Output 'False'} Write-Output 'True'
} }
else {
Write-Output 'False'
}
}
test ($null) # => False test ($null) # => False
test (0) # => False test (0) # => False
test ("") # => False test ("") # => False
test [] # => True test [] # => True *[] Not valid in Powershell, creates null-valued expression
test ({}) # => True test ({}) # => True
test @() # => False test @() # => False
<#
IsPublic IsSerial Name BaseType
-------- -------- ---- --------
True True Int32 System.ValueType
True True Int32 System.ValueType
True True String System.Object
You cannot call a method on a null-valued expression.
At line:4 char:1
+ $test3.getType()
+ ~~~~~~~~~~~~~~~~
+ CategoryInfo : InvalidOperation: (:) [], RuntimeException
+ FullyQualifiedErrorId : InvokeMethodOnNull
True True ScriptBlock System.Object
True True Object[] System.Array
#>
#################################################### ####################################################
## 2. Variables and Collections ## 2. Variables and Collections
#################################################### ####################################################
# Powershell uses the "Write-Output" function to print # Powershell uses the "Write-Output" function to print
Write-Output "I'm Powershell. Nice to meet you!" # => I'm Powershell. Nice to meet you! Write-Output "I'm Posh. Nice to meet you!" # => I'm Posh. Nice to meet you!
# Simple way to get input data from console # Simple way to get input data from console
$userInput = Read-Host "Enter some data: " # Returns the data as a string $userInput = Read-Host "Enter some data: " # Returns the data as a string
@ -367,7 +391,6 @@ switch($val) {
{ $_ -like 's*' } { "Case insensitive"; break } { $_ -like 's*' } { "Case insensitive"; break }
{ $_ -clike 's*'} { "clike, ceq, cne for case sensitive"; break } { $_ -clike 's*'} { "clike, ceq, cne for case sensitive"; break }
{ $_ -notmatch '^.*$'} { "Regex matching. cnotmatch, cnotlike, ..."; break } { $_ -notmatch '^.*$'} { "Regex matching. cnotmatch, cnotlike, ..."; break }
{ 'x' -contains 'x'} { "FALSE! -contains is for lists!"; break }
default { "Others" } default { "Others" }
} }
@ -384,7 +407,6 @@ finally {
} }
# Writing to a file # Writing to a file
$contents = @{"aa"= 12 $contents = @{"aa"= 12
"bb"= 21} "bb"= 21}
@ -532,6 +554,7 @@ True False Guitar Instrument
#> #>
#################################################### ####################################################
## 7. Advanced ## 7. Advanced
#################################################### ####################################################
@ -582,7 +605,7 @@ $Area
This is a silly one This is a silly one
You may one day be asked to create a func that could take $start and $end You may one day be asked to create a func that could take $start and $end
and reverse anything in an array within the given range and reverse anything in an array within the given range
based on an arbitrary array based on an arbitrary array without mutating the original array
Let's see one way to do that and introduce another data structure Let's see one way to do that and introduce another data structure
#> #>
@ -599,7 +622,7 @@ function Format-Range ($start, $end) {
elseif ($index -ge $start -and $index -le $end) { elseif ($index -ge $start -and $index -le $end) {
$stack.Push($targetArray[$index]) $stack.Push($targetArray[$index])
} }
elseif ($index -gt $end) { else {
$secondSectionArray.Add($targetArray[$index]) > $null $secondSectionArray.Add($targetArray[$index]) > $null
} }
} }
@ -607,6 +630,8 @@ function Format-Range ($start, $end) {
Write-Output $returnArray Write-Output $returnArray
} }
Format-Range 2 6 # => 'a','b','g','f','e','d','c','h','i','j','k','l','m','n'
# The previous method works, but it uses extra memory by allocating new arrays # The previous method works, but it uses extra memory by allocating new arrays
# It's also kind of lengthy # It's also kind of lengthy
# Let's see how we can do this without allocating a new array # Let's see how we can do this without allocating a new array
@ -623,10 +648,13 @@ function Format-Range ($start, $end) {
} }
return $targetArray return $targetArray
} }
Format-Range 2 6 # => 'a','b','g','f','e','d','c','h','i','j','k','l','m','n'
``` ```
Powershell as a Tool: Powershell as a Tool:
Getting Help: Getting Help:
```Powershell ```Powershell
# Find commands # Find commands
Get-Command about_* # alias: gcm Get-Command about_* # alias: gcm