How do I check a string exist in a file using PowerShell? - string

Question

I have a 1st text file looks like this : 12AB34.US. The second text file is CD 34 EF.
I want to find my 2nd text file exist or not in the 1st text file.
I tried to cut 3 characters last in the first text file (.US). Then I split to each 2 characters (because the 2nd text file consist of 2 characters). Then, I tried this code, and it always return "Not Found".
$String = Get-Content "C:\Users\te2.txt"
$Data = Get-Content "C:\Users\Fixed.txt"
$Split = $Data -split '(..)'
$Cut = $String.Substring(0,6)
$String_Split = $Cut -split '(..)'
$String_Split
$Check= $String_Split | %{$_ -match $Split}
if ($Check-contains $true) {
Write-Host "0"
} else {
Write-Host "1"
}

Answer 1

There are a number of problems with your current approach.
The 2-char groups don't align:
# strings split into groups of two
'12' 'AB' '34' # first string
'CD' ' 3' '4 ' # second string
When you test multiple strings with -match, you need to
escape the input string to avoid matchings on meta characters (like .), and
place the collection on the left-hand side of the operator, the pattern on the right:
$Compare = $FBString_Split | % {$Data_Split -match [regex]::Escape($_)}
if ($Compare -contains $true) {
Write-Host "Found"
} else {
Write-Host "Not Found"
}
For a more general solution to find out if any substring of N chars of one string is also a substring of another, you could probably do something like this instead:
$a = '12AB34.US'
$b = 'CD 34 EF'
# we want to test all substrings of length 2
$n = 2
$possibleSubstrings = 0..($n - 1) | ForEach-Object {
# grab substrings of length $n at every offset from 0 to $n
$a.Substring($_) -split "($('.'*$n))" | Where-Object Length -eq $n |ForEach-Object {
# escape the substring for later use with `-match`
[regex]::Escape($_)
}
} |Sort-Object -Unique
# We can construct a single regex pattern for all possible substrings:
$pattern = $possibleSubstrings -join '|'
# And finally we test if it matches
if($b -match $pattern){
Write-Host "Found!"
}
else {
Write-Host "Not found!"
}
This approach will give you the correct answer, but it'll become extremely slow on large inputs, at which point you may want to look at non-regex based strategies like Boyer-Moore