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:

<span><span><span><span><span></span></span></span></span></span>

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

<span></span>

Yet in others it is like this:

<span><span></span></span>

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:

<span style="font-weight:bold;">text</span>

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 '<span>', '' `
       -replace '</span>', ''
} | Set-Content $destination_file

...but obviously results in something like text.

In the PowerShell script above I can use

    $_ -replace '<span></span>', '' `

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 '<span></span>', '' `
       -replace '<span></span>', '' `
       -replace '<span></span>', '' `
       -replace '<span></span>', '' `
       -replace '<span></span>', '' 
} | 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.

user6811411 · Accepted Answer · 2018-11-11 13:12:48Z

1

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 "(<span>)+(</span>)+" | 
 Set-Content $destination_file

answered Nov 11, 2018 at 13:12

user6811411

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Comments

Guenther Schmitz · Accepted Answer · 2018-11-10 18:22:43Z

1

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

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

$patternToBeRemoved = '<span></span>'

# 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

answered Nov 10, 2018 at 18:22

Guenther Schmitz

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1 Comment

hcdocs Over a year ago

Thank you for the explanatory comments @guenther

ErikW · Accepted Answer · 2018-11-10 18:24:11Z

0

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

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

answered Nov 10, 2018 at 18:24

ErikW

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Comments

Manuel Batsching · Accepted Answer · 2018-11-10 18:49:25Z

0

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 = '<span></span><span><span><span style="font-weight:bold;">Foo</span></span></span>'
$regex = '<span>(.*?)</span>'    
while ($content -match $regex)
{
    $content = $content -replace $regex,'$1'
}
Write-Output $content

The result will be:

<span style="font-weight:bold;">Foo</span>

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

edited Nov 10, 2018 at 18:49

answered Nov 10, 2018 at 18:19

Manuel Batsching

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Comments

walid · Accepted Answer · 2018-11-11 00:13:20Z

0

$content = '<span></span><span><span><span style="font-weight:bold;">Foo</span></span></span>'
$regex = '<span\s+[^<]+</span>'
$null = $content -match $regex

$Matches[0]

answered Nov 11, 2018 at 0:13

walid

1

1 Comment

Elletlar Over a year ago

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