Loop search and replace two-part string over file using PowerShell while preserving one of the parts

Question

I am new at PowerShell and have not found a Stack Overflow question or a documentation reference that gets me all the way to a successful outcome. If a question or documentation reference already exists that answers this that I overlooked I would be grateful to know.

In a text file is a string like this:

The number of and varies from file to file. For example, in some files it is like this:

Yet in others it is like this:

And so on. There are likely never going to be more than 24 of each in a string.

I want to eliminate all strings like this in the text file, yet preserve the in strings like this:

text

There may be many variations on that kind of string in the text file; for example, text or text and I don't know beforehand what variation(s) will be included in the text file.

This partially works...

$original_file = 'in.txt'
$destination_file = 'out.txt'

(Get-Content $original_file) | Foreach-Object {
    $_ -replace '', '' `
       -replace '', ''
} | Set-Content $destination_file

...but obviously results in something like text.

In the PowerShell script above I can use

    $_ -replace '', '' `

But of course it only catches the in the middle of the string because, as it is written now, it does not loop.

I know it is silly to do something like this

$original_file = 'in.txt'
$destination_file = 'out.txt'

(Get-Content $original_file) | Foreach-Object {
    $_ -replace '', '' `
       -replace '', '' `
       -replace '', '' `
       -replace '', '' `
       -replace '', '' 
} | Set-Content $destination_file

So because the string collapses into itself each time the script is run, producing a new inner that can then be removed, the best solution I can think of is to loop the script over the file until it recognizes that all instances of are gone.

I feel like adding logic along these lines is necessary:

   foreach($i in 1..24){
    Write-Host $i

But have not been able to successfully incorporate it into the script.

If this is the wrong approach entirely I would be grateful to know.

The reason for PowerShell is that my team prefers it for scripts included in an Azure DevOps release pipeline.

Thanks for any ideas or help.

user_7414237 · Answer

Try the following .. i've added some comments to clearify things.

# always use absolute paths if possible
$original_file = 'c:	mp\in.txt'
$destination_file = 'c:	mp\out.txt'

$patternToBeRemoved = ''

# store the file contents in a variable
$fileContent = Get-Content -Path $original_file

# save the result of these operations in a new variable and iterate through each line
$newContent = foreach($string in $fileContent) {
    # while the pattern you don't want is found it will be removed
    while($string.Contains($patternToBeRemoved)) {
        $string = $string.Replace($patternToBeRemoved, '')
    }
    # when it's no longer found the new string is returned
    $string
}

# save the new content in the destination file
Set-Content -Path $destination_file -Value $newContent

Admin · Answer

If you just want to remove any number of empty spans use a Regular Expression with a group and a quantifier:

$original_file = 'in.txt'
$destination_file = 'out.txt'

(Get-Content $original_file) -replace "()+()+" | 
 Set-Content $destination_file

user_565359 · Answer

You can use a regular expression together with the -replace operator to strip all optional content pairs from a string. That means all pairs where the opening tag does not specify any attributes.

$content = 'Foo'
$regex = '(.*?)'    
while ($content -match $regex)
{
    $content = $content -replace $regex,'$1'
}
Write-Output $content

The result will be:

Foo

The while loop takes care of your nested occurrences of the pair.

user_10038952 · Answer

$original_file = 'in.txt'
$destination_file = 'out.txt'

ForEach ($Line in (Get-Content $original_file)) {
    Do {
        $Line = $Line -replace '',''
    } While ($Line -match '')
    Set-Content -Path $destination_file -Value $Line 
}

user_10634672 · Answer

$content = 'Foo'
$regex = ''
$null = $content -match $regex

$Matches[0]

Loop search and replace two-part string over file using PowerShell while preserving one of the parts

5 Answers