Looping through a hash, or using an array in PowerShell

Question

I'm using this (simplified) chunk of code to extract a set of tables from SQL Server with BCP.

$OutputDirectory = "c:\junk\" $ServerOption =   "-SServerName" $TargetDatabase = "Content.dbo."  $ExtractTables = @(     "Page"     , "ChecklistItemCategory"     , "ChecklistItem" )  for ($i=0; $i -le $ExtractTables.Length – 1; $i++)  {     $InputFullTableName = "$TargetDatabase$($ExtractTables[$i])"     $OutputFullFileName = "$OutputDirectory$($ExtractTables[$i])"     bcp $InputFullTableName out $OutputFullFileName -T -c $ServerOption } 

It works great, but now some of the tables need to be extracted via views, and some don't. So I need a data structure something like this:

"Page"                      "vExtractPage" , "ChecklistItemCategory"   "ChecklistItemCategory" , "ChecklistItem"           "vExtractChecklistItem" 

I was looking at hashes, but I'm not finding anything on how to loop through a hash. What would be the right thing to do here? Perhaps just use an array, but with both values, separated by space?

Or am I missing something obvious?

Answer 1

Shorthand is not preferred for scripts; it is less readable. The %{} operator is considered shorthand. Here's how it should be done in a script for readability and reusability:

Variable Setup

PS> $hash = @{     a = 1     b = 2     c = 3 } PS> $hash  Name                           Value ----                           ----- c                              3 b                              2 a                              1 

Option 1: GetEnumerator()

Note: personal preference; syntax is easier to read

The GetEnumerator() method would be done as shown:

foreach ($h in $hash.GetEnumerator()) {     Write-Host "$($h.Name): $($h.Value)" } 

Output:

c: 3 b: 2 a: 1 

Option 2: Keys

The Keys method would be done as shown:

foreach ($h in $hash.Keys) {     Write-Host "${h}: $($hash.$h)" } 

Output:

c: 3 b: 2 a: 1 

Additional information

Be careful sorting your hashtable...

Sort-Object may change it to an array:

PS> $hash.GetType()  IsPublic IsSerial Name                                     BaseType -------- -------- ----                                     -------- True     True     Hashtable                                System.Object   PS> $hash = $hash.GetEnumerator() | Sort-Object Name PS> $hash.GetType()  IsPublic IsSerial Name                                     BaseType -------- -------- ----                                     -------- True     True     Object[]                                 System.Array 

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This and other PowerShell looping are available on my blog.