While I was busy working, it turned into Friday which means time for a little PowerShell fun. I can't say you'll find any deep, meaningful, production use from today's post, but you might pick up a few techniques, which is really the point. Today we're going to have some fun with strings and arrays.<\/p>\n
The first thing I want to do is reverse a string. So that a string like \"Every good boy deserves fudge\" becomes \"egduf sevresed yob doog yrevE\". This is also a great example of how we can take advantage of the object nature of PowerShell. Without nitpicking the semantics, I'm not parsing the string to get a reverse version, I'm taking advantage of objects. First off, a string object has a single property: length.
\n[cc lang=\"PowerShell\"]
\nPS C:\\> $s=\"PowerShell\"
\nPS C:\\> $s.length
\n10
\nPS C:\\>
\n[\/cc]
\nThe string object is also an array of characters which means I can access any character I want by an index number. Remember PowerShell arrays start at 0.
\n[cc lang=\"PowerShell\"]
\nPS C:\\> $s[4]
\nr
\nPS C:\\> $s[5]
\nS
\nPS C:\\> $s[0,6]
\nP
\nh
\nPS C:\\> $s[3..6]
\ne
\nr
\nS
\nh
\nPS C:\\>
\n[\/cc]
\nSo to reverse the string, all I need to do is get the characters in reverse order and build a new string.
\n[cc lang=\"PowerShell\"]
\nPS C:\\> [string]$reverse=\"\"
\nPS C:\\> for ($i=($s.length-1);$i -ge 0; $i--) {
\n>> #append to $reverse
\n>> $reverse+=$s[$i]
\n>> }
\n>>
\nPS C:\\> $reverse
\nllehSrewoP
\nPS C:\\>
\n[\/cc]
\nI defined an empty string object, and then using the FOR construct start at the end of $s and add each character to $reverse. Taking this a step further I put together a function, Out-Reverse, so that you could pipe strings, or even entire text files to it. Each reversed line will be written to the pipeline.
\n[cc lang=\"PowerShell\"]
\nFunction Out-Reverse {<\/p>\n
Param(
\n[Parameter(Position=0,Mandatory=$True,HelpMessage=\"Enter a line of text\",
\nValueFromPipeline=$True)]
\n[ValidateNotNullorEmpty()]
\n[string[]]$Text
\n)<\/p>\n
Process {
\n ForEach ($str in $Text) {
\n Write-Verbose \"Reversing: $str\"
\n $str | foreach {
\n #define an empty variable for the reversed result
\n [string]$reverse=\"\"
\n for ($i=($_.length-1);$i -ge 0; $i--) {
\n #append to $reverse
\n $reverse+=$_[$i]
\n }
\n #write the result
\n Write-Host \"Reversed\" -ForegroundColor Yellow
\n $reverse
\n }
\n }# Foreach
\n} #process<\/p>\n
} #end function
\n[\/cc]
\nWant to see it in action?
\n[cc lang=\"PowerShell\"]
\nPS C:\\> \"The quick brown fox jumped over the lazy dog\" | out-reverse
\nReversed
\ngod yzal eht revo depmuj xof nworb kciuq ehT
\n[\/cc]The function uses Write-Host to show you what happened but you could comment that out. Now let's look at one other way to play with strings.<\/p>\n
Since we know the string is an array of characters which we can access by index number. let's create a randomized version of the string. Naturally I made a function.
\n[cc lang=\"PowerShell\"]
\nFunction Out-Random {<\/p>\n
Param(
\n[Parameter(Position=0,Mandatory=$True,HelpMessage=\"Enter a line of text\",
\nValueFromPipeline=$True)]
\n[ValidateNotNullorEmpty()]
\n[string[]]$Text
\n)<\/p>\n
Process {
\n ForEach ($str in $Text) {
\n Write-Verbose \"Randomizing: $str\"
\n #initialize an empty array
\n $a=@()
\n Write-Verbose \"Generating random number array\"
\n do {
\n #get a random number between 0 and length of string
\n $x=get-random -Minimum 0 -Maximum $str.length
\n #add the number to the array if it doesn't already exist
\n if (-not ($a -contains $x)) {
\n $a+=$x
\n }
\n #repeat until every number has been added to the array
\n } Until ($a.count -eq $str.length)<\/p>\n
#define a varialble for the randomized output
\n [string]$randout=\"\"
\n Write-Verbose \"Constructing random output\"
\n #get the corresponding random element and construct the random output
\n $a | foreach { $randout+=$str[$_] }
\n #write the result
\n Write-Host \"Randomized\" -ForegroundColor Yellow
\n $randout
\n } #foreach
\n } #Process
\n} #end function
\n[\/cc]<\/p>\n
Now I couldn't just get a random number for each character in the array because I'd end up with duplicates. If the string was 10 characters long, then I need an array of numbers 0 to 9 in a random order. To accomplish my goal, I created an empty array. Then using the Get-Random cmdlet, I generated a number between 0 and the string length. If the number did not already exist in my empty array I add it, otherwise I looped and tried again. I hope this is a good example of a Do\/Until loop.
\n[cc lang=\"PowerShell\"]
\n$a=@()
\n Write-Verbose \"Generating random number array\"
\n do {
\n #get a random number between 0 and length of string
\n $x=get-random -Minimum 0 -Maximum $str.length
\n #add the number to the array if it doesn't already exist
\n if (-not ($a -contains $x)) {
\n $a+=$x
\n }
\n #repeat until every number has been added to the array
\n } Until ($a.count -eq $str.length)
\n[\/cc]
\nThe process continues until the number of items in my array equals the length of the string. Now, it's just a matter of enumerating the array of random numbers, getting the corresponding character from the string array and building a new string.
\n[cc lang=\"Powershell\"]
\n [string]$randout=\"\"
\n Write-Verbose \"Constructing random output\"
\n #get the corresponding random element and construct the random output
\n $a | foreach { $randout+=$str[$_] }
\n[\/cc]
\nMy Out-Reverse function in action:
\n[cc lang=\"PowerShell\"]
\nPS C:\\> \"The quick brown fox jumped over the lazy dog\" | out-random
\nRandomized
\neine gdoxk mu o buazloeorcfhqv dt pjThwyre
\n[\/cc]
\nYou can have even more fun by piping between functions.
\n[cc lang=\"PowerShell\"]
\nPS C:\\> \"Every good boy deserves fudge\" | out-reverse | out-random
\nReversed
\nRandomized
\nsdr yedesbdreoeyefvEv og guo
\nPS C:\\> \"Every good boy deserves fudge\" | out-random | out-reverse
\nRandomized
\nReversed
\n dfdgeuoesyb rogs er dyeEvevo
\nPS C:\\> \"Every good boy deserves fudge\" | out-reverse | out-reverse
\nReversed
\nReversed
\nEvery good boy deserves fudge
\n[\/cc]
\nThe last example is kind of silly. But it shows you can undo the change. Actually, if you save the randomized array ($a), you can also \"decode\" the randomized string. But I'll leave that for you to play with. A hint: you'll most likely need a hash table.<\/p>\n