How do I change foreach to for in PowerShell? - powershell

Question

I want to print the word exist in a text file and print "match" and "not match". My 1st text file is: xxaavv6J, my 2nd file is 6J6SCa.yB.
If it is match, it return like this:
Match found:
Match found:
Match found:
Match found:
Match found:
Match found: 6J
Match found:
Match found:
Match found:
My expectation is just print match and not match.
$X = Get-Content "C:\Users\2.txt"
$Data = Get-Content "C:\Users\d.txt"
$Split = $Data -split '(..)'
$Y = $X.Substring(0, 6)
$Z = $Y -split '(..)'
foreach ($i in $Z) {
foreach ($j in $Split) {
if ($i -like $j) {
Write-Host ("Match found: {0}" -f $i, $j)
}
}
}

Answer 1

The operation -split '(..)' does not produce the result you think it does. If you take a look at the output of the following command you'll see that you're getting a lot of empty results:
PS C:\> 'xxaavv6J' -split '(..)' | % { "-$_-" }
--
-xx-
--
-aa-
--
-vv-
--
-6J-
--
Those empty values are the additional matches you're getting from $i -like $j.
I'm not quite sure why -split '(..)' gives you any non-empty values in the first place, because I would have expected it to produce 5 empty strings for an input string "xxaavv6J". Apparently it has to do with the grouping parentheses, since -split '..' (without the grouping parentheses) actually does behave as expected. Looks like with the capturing group the captured matches are returned on top of the results of the split operation.
Anyway, to get the behavior you want replace
... -split '(..)'
with
... |
Select-String '..' -AllMatches |
Select-Object -Expand Matches |
Select-Object -Expand Value
You can also replace the nested loop with something like this:
foreach ($i in $Z) {
if (if $Split -contains $i) {
Write-Host "Match found: ${i}"
}
}

Answer 2

A slightly different approach using regex '.Match()' should also do it.
I have added a lot of explaining comments for you:
$Test = Get-Content "C:\Users\2.txt" -Raw # Read as single string. Contains "xxaavv6J"
$Data = (Get-Content "C:\Users\d.txt") -join '' # Read as array and join the lines with an empty string.
# This will remove Newlines. Contains "6J6SCa.yB"
# Split the data and make sure every substring has two characters
# In each substring, the regex special characters need to be Escaped.
# When this is done, we join the substrings together using the pipe symbol.
$Data = ($Data -split '(.{2})' | # split on every two characters
Where-Object { $_.Length -eq 2 } | # don't care about any left over character
ForEach-Object { [Regex]::Escape($_) } ) -join '|' # join with the '|' which is an OR in regular expression
# $Data is now a string to use with regular expression: "6J|6S|Ca|\.y"
# Using '.Match()' works Case-Sensitive. To have it compare Case-Insensitive, we do this:
$Data = '(?i)' + $Data
# See if we can find one or more matches
$regex = [regex]$Data
$match = $regex.Match($Test)
# If we have found at least one match:
if ($match.Groups.Count) {
while ($match.Success) {
# matched text: $match.Value
# match start: $match.Index
# match length: $match.Length
Write-Host ("Match found: {0}" -f $match.Value)
$match = $match.NextMatch()
}
}
else {
Write-Host "Not Found"
}
Result:
Match found: 6J

Answer 3

Further to the excellent Ansgar Wiechers' answer: if you are running (above) Windows PowerShell 4.0 then you could apply the .Where() method described in Kirk Munro's exhaustive article ForEach and Where magic methods:
With the release of Windows PowerShell 4.0, two new “magic” methods
were introduced for collection types that provide a new syntax for
accessing ForEach and Where capabilities in Windows PowerShell.
These methods are aptly named ForEach and Where. I call
these methods “magic” because they are quite magical in how they work
in PowerShell. They don’t show up in Get-Member output, even if you
apply -Force and request -MemberType All. If you roll up your
sleeves and dig in with reflection, you can find them; however, it
requires a broad search because they are private extension methods
implemented on a private class. Yet even though they are not
discoverable without peeking under the covers, they are there when you
need them, they are faster than their older counterparts, and they
include functionality that was not available in their older
counterparts, hence the “magic” feeling they leave you with when you
use them in PowerShell. Unfortunately, these methods remain
undocumented even today, almost a year since they were publicly
released, so many people don’t realize the power that is available in
these methods.
…
The Where method
Where is a method that allows you to filter a collection of objects.
This is very much like the Where-Object cmdlet, but the Where
method is also like Select-Object and Group-Object as well,
includes several additional features that the Where-Object cmdlet
does not natively support by itself. This method provides faster
performance than Where-Object in a simple, elegant command. Like
the ForEach method, any objects that are output by this method are
returned in a generic collection of type
System.Collections.ObjectModel.Collection1[psobject].
There is only one version of this method, which can be described as
follows:
Where(scriptblock expression[, WhereOperatorSelectionMode mode[, int numberToReturn]])
As indicated by the square brackets, the expression script block is
required and the mode enumeration and the numberToReturn integer
argument are optional, so you can invoke this method using 1, 2, or 3
arguments. If you want to use a particular argument, you must provide
all arguments to the left of that argument (i.e. if you want to
provide a value for numberToReturn, you must provide values for
mode and expression as well).
Applied to your case (using the simplest variant Where(scriptblock expression) of the .Where() method):
$X = '6J6SCa.yB' # Get-Content "C:\Users\2.txt"
$Data = 'xxaavv6J' # Get-Content "C:\Users\d.txt"
$Split = ($Data -split '(..)').Where({$_ -ne ''})
$Y = $X.Substring(0, 6)
$Z = ($Y -split '(..)').Where{$_ -ne ''} # without parentheses
For instance, Ansgar's example changes as follows:
PS > ('xxaavv6J' -split '(..)').Where{$_ -ne ''} | % { "-$_-" }
-xx-
-aa-
-vv-
-6J-