how to understand foreach loop in powershell - powershell

Hi every one I am new to power shell and trying to make sense about for each loop but I don't understand what does + $ means in the below script and why they are used together
$names = "jones","mike","Ash"
foreach ($name in $names)
{
"$name = " + $name.length
}

First of all, it is PowerShell. There is no space and observe the capitalization of letters.
Second, RTFM. There is a lot of documentation on Technet. Make use of that. There is built-in help. Read Help about_* topics.
Coming to your question, the foreach loop iterates over all collection. In your example, $names is an array of strings. An array is a collection.
In your example, when the foreach loop iterates over the collection, it copies each item in the collection to another variable called $name.
foreach ($name in $names) {}
Inside the foreach loop, you can use the $name variable to retrieve the value stored in the item. So, the following code will print the values in the collection.
foreach ($name in $names) {
$name
}
$name is a string. So, $name.Length gives us the length of that string.
+ is an arithmetic operator. It can be used to concatenate strings. In this case, $name + $name.length will result in the value getting appended with the length.
Here is the modified example with output:
$names = "jones","mike","Ash"
foreach ($name in $names)
{
$name + $name.Length
}
jones5
mike4
Ash3
Finally, coming to your example and the output:
$names = "jones","mike","Ash"
foreach ($name in $names)
{
"$name = " + $name.Length
}
jones = 5
mike = 4
Ash = 3
I hope this provides some explanation for you on what the example is doing.

Let's see this step by step:
$names = "jones","mike","Ash"
This declares an array with three string items and stores it in the $names variable.
foreach ($name in $names) { }
This is a loop that iterates through all items in the $names array variable. Each item is "copied" into the "$name" variable, so when you're working with $name, you are working with the current item in the loop.
"$name = " + $name.length
This outputs the contents of the $name variable and the "length" property of the object represented by $name. If you recall, we declared an array of string items, in other words string objects. Strings objects have properties and methods, one of those properties is the length property that tells how long the string is.
The notation is a bit odd, though. In PowerShell, variables embedded into string literals (e.g. "start $name end" will be replaced with their string value, so "start $name end" will become start jones end for the first item. However, you can't just write "start $name.length end", so in this example the author used + to concatenate (append) the two strings. An alternative solution to that would be "$name = $($name.length))": this way a single string literal would contain both the string and its length property.

Related

Check if a condition is met by a line within a TXT but "in an advanced way"

I have a TXT file with 1300 megabytes (huge thing). I want to build code that does two things:
Every line contains a unique ID at the beginning. I want to check for all lines with the same unique ID if the conditions is met for that "group" of IDs. (This answers me: For how many lines with the unique ID X have all conditions been met)
If the script is finished I want to remove all lines from the TXT where the condition was met (see 2). So I can rerun the script with another condition set to "narrow down" the whole document.
After few cycles I finally have a set of conditions that applies to all lines in the document.
It seems that my current approach is very slow.( one cycle needs hours). My final result is a set of conditions that apply to all lines of code.
If you find an easier way to do that, feel free to recommend.
Help is welcome :)
Code so far (does not fullfill everything from 1&2)
foreach ($item in $liste)
{
# Check Conditions
if ( ($item -like "*XXX*") -and ($item -like "*YYY*") -and ($item -notlike "*ZZZ*")) {
# Add a line to a document to see which lines match condition
Add-Content "C:\Desktop\it_seems_to_match.txt" "$item"
# Retrieve the unique ID from the line and feed array.
$array += $item.Split("/")[1]
# Remove the line from final document
$liste = $liste -replace $item, ""
}
}
# Pipe the "new cleaned" list somewhere
$liste | Set-Content -Path "C:\NewListToWorkWith.txt"
# Show me the counts
$array | group | % { $h = #{} } { $h[$_.Name] = $_.Count } { $h } | Out-File "C:\Desktop\count.txt"
Demo Lines:
images/STRINGA/2XXXXXXXX_rTTTTw_GGGG1_Top_MMM1_YY02_ZZZ30_AAAA5.jpg images/STRINGA/3XXXXXXXX_rTTTTw_GGGG1_Top_MMM1_YY02_ZZZ30_AAAA5.jpg images/STRINGB/4XXXXXXXX_rTTTTw_GGGG1_Top_MMM1_YY02_ZZZ30_AAAA5.jpg images/STRINGB/5XXXXXXXX_rTTTTw_GGGG1_Top_MMM1_YY02_ZZZ30_AAAA5.jpg images/STRINGC/5XXXXXXXX_rTTTTw_GGGG1_Top_MMM1_YY02_ZZZ30_AAAA5.jpg
performance considerations:
Add-Content "C:\Desktop\it_seems_to_match.txt" "$item"
try to avoid wrapping cmdlet pipelines
See also: Mastering the (steppable) pipeline
$array += $item.Split("/")[1]
Try to avoid using the increase assignment operator (+=) to create a collection
See also: Why should I avoid using the increase assignment operator (+=) to create a collection
$liste = $liste -replace $item, ""
This is a very expensive operation considering that you are reassigning (copying) a long list ($liste) with each iteration.
Besides it is a bad practice to change an array that you are currently iterating.
$array | group | ...
Group-Object is a rather slow cmdlet, you better collect (or count) the items on-the-fly (where you do $array += $item.Split("/")[1]) using a hashtable, something like:
$Name = $item.Split("/")[1]
if (!$HashTable.Contains($Name)) { $HashTable[$Name] = [Collections.Generic.List[String]]::new() }
$HashTable[$Name].Add($Item)
To minimize memory usage it may be better to read one line at a time and check if it already exists. Below code I used StringReader and you can replace with StreamReader for reading from a file. I'm checking if the entire string exists, but you may want to split the line. Notice I have duplicaes in the input but not in the dictionary. See code below :
$rows= #"
images/STRINGA/2XXXXXXXX_rTTTTw_GGGG1_Top_MMM1_YY02_ZZZ30_AAAA5.jpg
images/STRINGA/3XXXXXXXX_rTTTTw_GGGG1_Top_MMM1_YY02_ZZZ30_AAAA5.jpg
images/STRINGB/4XXXXXXXX_rTTTTw_GGGG1_Top_MMM1_YY02_ZZZ30_AAAA5.jpg
images/STRINGB/5XXXXXXXX_rTTTTw_GGGG1_Top_MMM1_YY02_ZZZ30_AAAA5.jpg
images/STRINGC/5XXXXXXXX_rTTTTw_GGGG1_Top_MMM1_YY02_ZZZ30_AAAA5.jpg
images/STRINGA/2XXXXXXXX_rTTTTw_GGGG1_Top_MMM1_YY02_ZZZ30_AAAA5.jpg
images/STRINGA/3XXXXXXXX_rTTTTw_GGGG1_Top_MMM1_YY02_ZZZ30_AAAA5.jpg
images/STRINGB/4XXXXXXXX_rTTTTw_GGGG1_Top_MMM1_YY02_ZZZ30_AAAA5.jpg
images/STRINGB/5XXXXXXXX_rTTTTw_GGGG1_Top_MMM1_YY02_ZZZ30_AAAA5.jpg
images/STRINGC/5XXXXXXXX_rTTTTw_GGGG1_Top_MMM1_YY02_ZZZ30_AAAA5.jpg
"#
$dict = [System.Collections.Generic.Dictionary[int, System.Collections.Generic.List[string]]]::new();
$reader = [System.IO.StringReader]::new($rows)
while(($row = $reader.ReadLine()) -ne $null)
{
$hash = $row.GetHashCode()
if($dict.ContainsKey($hash))
{
#check if list contains the string
if($dict[$hash].Contains($row))
{
#string is a duplicate
}
else
{
#add string to dictionary value if it is not in list
$list = $dict[$hash].Value
$list.Add($row)
}
}
else
{
#add new hash value to dictionary
$list = [System.Collections.Generic.List[string]]::new();
$list.Add($row)
$dict.Add($hash, $list)
}
}
$dict

Powershell passing multiple parameters from one script to another [duplicate]

I've seen the # symbol used in PowerShell to initialise arrays.
What exactly does the # symbol denote and where can I read more about it?
In PowerShell V2, # is also the Splat operator.
PS> # First use it to create a hashtable of parameters:
PS> $params = #{path = "c:\temp"; Recurse= $true}
PS> # Then use it to SPLAT the parameters - which is to say to expand a hash table
PS> # into a set of command line parameters.
PS> dir #params
PS> # That was the equivalent of:
PS> dir -Path c:\temp -Recurse:$true
PowerShell will actually treat any comma-separated list as an array:
"server1","server2"
So the # is optional in those cases. However, for associative arrays, the # is required:
#{"Key"="Value";"Key2"="Value2"}
Officially, # is the "array operator." You can read more about it in the documentation that installed along with PowerShell, or in a book like "Windows PowerShell: TFM," which I co-authored.
While the above responses provide most of the answer it is useful--even this late to the question--to provide the full answer, to wit:
Array sub-expression (see about_arrays)
Forces the value to be an array, even if a singleton or a null, e.g. $a = #(ps | where name -like 'foo')
Hash initializer (see about_hash_tables)
Initializes a hash table with key-value pairs, e.g.
$HashArguments = #{ Path = "test.txt"; Destination = "test2.txt"; WhatIf = $true }
Splatting (see about_splatting)
Let's you invoke a cmdlet with parameters from an array or a hash-table rather than the more customary individually enumerated parameters, e.g. using the hash table just above, Copy-Item #HashArguments
Here strings (see about_quoting_rules)
Let's you create strings with easily embedded quotes, typically used for multi-line strings, e.g.:
$data = #"
line one
line two
something "quoted" here
"#
Because this type of question (what does 'x' notation mean in PowerShell?) is so common here on StackOverflow as well as in many reader comments, I put together a lexicon of PowerShell punctuation, just published on Simple-Talk.com. Read all about # as well as % and # and $_ and ? and more at The Complete Guide to PowerShell Punctuation. Attached to the article is this wallchart that gives you everything on a single sheet:
You can also wrap the output of a cmdlet (or pipeline) in #() to ensure that what you get back is an array rather than a single item.
For instance, dir usually returns a list, but depending on the options, it might return a single object. If you are planning on iterating through the results with a foreach-object, you need to make sure you get a list back. Here's a contrived example:
$results = #( dir c:\autoexec.bat)
One more thing... an empty array (like to initialize a variable) is denoted #().
The Splatting Operator
To create an array, we create a variable and assign the array. Arrays are noted by the "#" symbol. Let's take the discussion above and use an array to connect to multiple remote computers:
$strComputers = #("Server1", "Server2", "Server3")<enter>
They are used for arrays and hashes.
PowerShell Tutorial 7: Accumulate, Recall, and Modify Data
Array Literals In PowerShell
I hope this helps to understand it a bit better.
You can store "values" within a key and return that value to do something.
In this case I have just provided #{a="";b="";c="";} and if not in the options i.e "keys" (a, b or c) then don't return a value
$array = #{
a = "test1";
b = "test2";
c = "test3"
}
foreach($elem in $array.GetEnumerator()){
if ($elem.key -eq "a"){
$key = $elem.key
$value = $elem.value
}
elseif ($elem.key -eq "b"){
$key = $elem.key
$value = $elem.value
}
elseif ($elem.key -eq "c"){
$key = $elem.key
$value = $elem.value
}
else{
Write-Host "No other value"
}
Write-Host "Key: " $key "Value: " $value
}

Powershell: combine contents of strings with dots inbetween, ignore empty ones

Our naming convention consists of the first name, insertion, and lastname, all separated by dots. An example:
Stack Overflow = Stack.Overflow
Stack over Flow = Stack.over.flow
These outputs will be used later on in the script for the creation of a mailbox, user account, etc.
I've successfully combined the values of all strings by simply plus-ing them together, like this:
$Convention = $Firstname+"."+$Insertion+"."+$LastName
The values for these strings come from information being put in when the stript runs (Read-Host "....")
Now, I'm struggling with making this more dynamic. Of course, not every person has an insertion in their name. Using the given example, the current output of $Convention would be "Stack..Overflow", instead of "Stack.Overflow".
My question to you is: how can I filter out both, the $Insertion and the extra dot, when $Insertion is empty? It's most likely something very simple, but I can't seem to figure out what it is.
Thanks in advance for any given help!
Kr,
Robbert
I would do
$Convention = ('{0}.{1}.{2}' -f $Firstname, $Insertion, $LastName) -replace '\.+', '.'
The -replace uses regex in the first parameter, so '\.+', '.' means to replace 1 or more consecutive dots by a single dot.
Alternatively you could use regex \.{2,} which reads two or more consecutive dots
Example:
$Firstname = 'Robbert'
$Insertion = ''
$LastName = 'Verwaart'
$Convention = ('{0}.{1}.{2}' -f $Firstname, $Insertion, $LastName) -replace '\.+', '.'
Output:
Robbert.Verwaart
The code below will go through each of your $convention array, if this is an array, and test if the insertion is empty. If the $Insertion variable is empty, the $i will remove the $Insertion variable and the extra .. You need to add this into the script as a test, before creating the mailboxes.
foreach ($i in $convention){
if($insertion -eq "" -or $insertion -eq $null) {
$i= $Firstname+"."+$LastName
} else {
continue
}
}

Count number of spaces, and split at the last one

I have a string simliar to:
c:/folder name/somewhere/application.exe instanceName
(n.b. the space in "folder name" is intentional) I need a way to split this into:
[0]c:/folder name/somewhere/application.exe
[1]instanceName
I was going to use split-path, but apparently there is a bug in powershell v2 that stops me doing this:
Split-Path : Cannot find drive. A drive with the name '
So, I figured if I count how many spaces there are, and then simply use -split() to split it at the last space.
But, I can't see how to count the number of spaces.
I've found lots of examples that talk about using regex to count complex strings, but I just want to count spaces!
Tonnes of ways to do this I imagine but to use your split idea you could do the following.
$split = "c:/folder name/somewhere/application.exe instanceName".Split(" ")
$path = $split[0..($split.count -2)] -Join " "
$instance = $split[-1]
Split the sting by spaces. The number of spaces is represented by the count of strings in the array $split. We join all the strings in the array accept the last intp $path then we take the last entry and assign it to $instance
You could also use .substring and .lastindexof
$string = "c:/folder name/somewhere/application.exe instanceName"
$index = $string.LastIndexOf(" ")
$string.Substring(0,$index)
$string.Substring($index + 1)
I can't see a way to split this directly into an array at this time but outputing as an array would not be a big deal.
$path, $instance
or
$array = #($path,$instance)
You can use a regular expression for this:
$s = "c:/folder name/somewhere/application.exe instanceName"
$s -match '(.*) (.*)$'
$matches[1]
$matches[2]
The special variable $matches is populated if the -match operation is true.
$matches[0] contains the original string, and other indexes will exist for the number of groups (patterns in parenthesis) in the regex. In this case: (.*) (.*)$ we have two groups.

Powershell being too clever

Apologies for what is probably a newbish question.
I am writing some Powershell scripts that run various queries against AD. They will usually return a bunch of results, which are easy to deal with, ie:
$results = myQuery
write-host "Returned " + $results.Count + " results."
foreach ($result in $results) { doSomething }
No worries. However, if there is only 1 result, Powershell automagically translates that result into a single object, rather than an array that contains 1 object. So the above code would break, both at the Count and the foreach. I'm sure the same problem would occur with 0 results.
Could someone suggest an elegant way to handle this? Perhaps some way to cast the results so they are always an array?
Change the first line of code to
$results = #(myQuery)
This will always return an array. See this blog entry for additional details.
Actually, the foreach works just fine. All uses of foreach (the foreach keyword, the Foreach-Object cmdlet, and Foreach-Object's aliases "foreach" and "%") all have the same behavior of "wrapping" the object in question in an array if needed. Thus, all uses of foreach will work with both scalar and array values.
Annoyingly, this means they work with null values too. Say I do:
$x = $null
foreach ($y in $x) {Write-Host "Hello world 1"}
$x | Foreach-Object {Write-Host "Hello world 2"}
I'll get
"Hello world 1"
"Hello world 2"
out of that.
This has bitten me as well. No clever ideas on how to fix $results.Count, but the foreach can be fixed by switching to a pipeline.
$scalar = 1
$list = (1,2)
$list | % { $_ }
prints
1
2
$scalar | % { $_ }
prints
1