Friday Fun What a CHAR!

Last week I posted a PowerShell snippet on Twitter. My original post piped an array of integers as [CHAR] type using an OFS. Don't worry about that. As many people reminded me, it is much easier to use the -Join operator.

-join [char[]](116,103,105,102)

I'll let you try that on your own. The [CHAR] type is used to represent a character as an integer value, like this:

PS C:\> [char]120
x

For this week's Friday Fun I thought it would be nice to translate a string of text into corresponding character values. It looks like a secret code! Or we could use the translation in a join scriptblock. So I put together a little script I call Translate-ToChar.ps1. The script takes a string of text and writes an array of [CHAR] objects.

Param(
[Parameter(Position=0)]
[ValidateNotNullOrEmpty()]
[string]$Text="PowerShell Rocks!",
[switch]$Scriptblock
)

#create CHAR mapping hash table
$map=@{}
33..125 | foreach { $map.Add([string]$_,[char]$_)}

#create an empty array to hold the CHAR values
$values=@()
$text.ToCharArray() | foreach {
#because $_ will change, save the current piped in character as a variable
$ltr=$_
[int]$i=($map.getEnumerator() | where {$_.value -ceq $ltr }).Name
#add the value to the array
$values+=$i
}

if ($ScriptBlock) {
#write a scriptblock to the pipeline
#create the command
$ofs=","
#create a variable so we variable expansion of $values
$t="-join [char[]]($values)"

#put it back together as a script block and write to the pipeline
[scriptblock]::Create($t)
}
else {
#write value array
$values
}

The script begins by defining a map hash table for what I think are all characters you are likely to find on a US keyboard. These should be character values 33 through 125 which I get using the range (..) operator.

$map=@{}
33..125 | foreach { $map.Add([string]$_,[char]$_)}

Each number is piped to ForEach object where I add it to the hash table. In order to get the hash table key to work properly I cast the number as a string and the hash table value is the same number cast as a [CHAR]. Now we can begin breaking the string apart and "translating" it.

$text.ToCharArray() | foreach {
#because $_ will change, save the current piped in character as a variable
$ltr=$_

The script splits the string into a character array using the default delimiter of a space. Because I'm going to be using a pipelined expression, I save the current letter as a variable. It will keep things straight in a moment.

The next step is to find the character in the hash table values. I found the best way to accomplish this was to call the hash table's GetEnumerator() method. This way I can pipe it to Where-Object and find the corresponding key.

[int]$i=($map.getEnumerator() | where {$_.value -ceq $ltr }).Name
#add the value to the array
$values+=$i

Notice I'm using the case sensitive -ceq operator. The Name property of the hash table enumerator is the key value, or in other words the corresponding [CHAR] integer. With me still? This value is added to an array for the final result. In fact the default is to simply write $values to the pipeline. But, I've included a -Scriptblock parameter to have the script write a scriptblock to the pipeline using the -Join operator I mentioned earlier. Now for the interesting part.

I have an array variable which needs to be expanded into the scriptblock. This won't work:

$sb={-join [char[]]($values)}
write $sb

I'll end up with a scriptblock but have no way of resolving $values once the script ends. So instead I create a string with $values knowing that PowerShell will expand it. And because I want the array to be expanded as a comma separated string, I'll specify the $ofs variable as a comma. The default is a space.

$ofs=","
#create a variable so we get variable expansion of $values
$t="-join [char[]]($values)"

The variable $t is now a string with all of the integer values from $values as a comma separated list. I can turn this into scriptblock like this:

#put it back together as a script block and write to the pipeline
[scriptblock]::Create($t)

The scriptblock gets written to the pipeline. So, I could run the script like this:

PS C:\scripts> $a=.\Translate-ToChar.ps1
PS C:\scripts> $a
80
111
119
101
114
83
104
101
108
108
0
82
111
99
107
115
33

Now I can use $a however I want. Or I could create a scriptblock.

PS C:\scripts> $b=.\Translate-ToChar.ps1 -Scriptblock
PS C:\scripts> $b
-join [char[]](80,111,119,101,114,83,104,101,108,108,0,82,111,99,107,115,33)

I can invoke $b anytime I want to see the message.

While I don't expect you to be running this in production I hope you picked up some tips on using hash tables, arrays, scriptblocks and casting variable types.

Download Translate-ToChar

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