PowerShell - Finding and modifying multiple text in string

Question

I've got the following text for example (stored as $test):

\u003c/p\u003e\n\u003cp\u003e\u003c/p\u003e\n\u003cimg src=\"/sites/mysite/SiteCollectionImages/banner.jpg\" alt=\"\" style=\"float:none;height: auto;width: auto\"/\u003e\n\u003cp\u003eMore Meat, Less Waste, Means More Value For Your Dollar.\u003c/p\u003e\n\u003cp\u003e\u003c/p\u003e\n\u003cp\u003eWhen substituting Emu meat in your recipes or planning your serving portions, keep in mind that low fat Emu meat will not shrink like other meats. You get more of what you pay for with no bones, exterior fat, or gristle. Emu meat is very shelf stable especially if vacuum packaged. Properly vacuum packaged meat will keep fresh in your refrigerator for up to 4 weeks, and up to 6-9 months in your freezer.\u003c/p\u003e\n\u003cp\u003e\u003c/p\u003e\n\u003cimg src=\"/sites/mysite/SiteCollectionImages/logo.jpg\" alt=\"\" style=\"float:none;height: auto;width: auto\"/\u003e\n\u003cp\u003e\u003c/p\u003e\n\u003cp\u003e\u003c/p\u003e\n\u003cp\u003e

I would like to update the bolded text in between img src=\" and \" (to something like /sites/newSite/newLibrary/originalFilename.v2.jpg)

How would I go about doing these replacements in Powershell using regex?

I've tried $test -replace '(?<=img src=\")(?<imgUrl>\")', ' ' to start and even that doesn't do any replacements for me.

Update

I was able to capture what I needed to replace by using $test -replace '(?<=img src=\\")(.+?)(?=\\")', '$1' (Thanks to @user1390638)

I wanted to apply a function to $1 before replacement so I had to do this to make it work:

[regex]::Replace($test, '(?<=img src=\\")(.+?)(?=\\")', {param($match) someFunction($match.Groups[1].Value) })

Updated my answer to apply a "scramble" function to the matches. — Ash
– Ash, Commented May 8, 2020 at 1:00

user1390638 · Accepted Answer · 2020-05-08 13:29:58Z

2

Your regex is wrong, to match the string between you should use the following regex.

First part of the regex (?<=img src=\") will find the img src=\" text inside your text variable. Note that you should escape \ character here.
Second part of the regex .+? gets everything between, ? means non-greedy, so it will stop at the first match
Last part of the regex (?=") means until quote.

(?<=img src=\\").+?(?=")

Assuming your text is assigned to $text variable.

$text -replace('(?<=img src=\\").+?(?=")',"/sites/newSite/newLibrary/originalFilename.v2.jpg")

To replace multiple texts, you can basically call -replace twice such as $text -replace(...) -replace(...)

edited May 8, 2020 at 13:29

answered May 8, 2020 at 0:07

user1390638

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3 Comments

kei Over a year ago

I see, but I still want to capture the match hence me using <imgUrl> so I can do some modifications on the replacement based on the original. How would I go about this? Basically the replacement text would be a parameter to some function that will give out the new image URL... so I was thinking of something like $test -replace [pattern<imgUrl>], someFunction(imgUrl). Is this even possible?

user1390638 Over a year ago

If what you want to do is to call the function on the input, you can assign the result into a variable like this $scrambled_url = scramble('$1') before calling replace, and then use this $scrambled_url variable in your replace function -replace('your pattern', $scrambled_url ) if this is what you want to do.

user1390638 Over a year ago

If you want to call function on the matched url, first you can get the matched url with -match $text -match '(?<=img src=\\").+?(?=")' once you call match, -match operator sets a special variable called $matches. You can get the matched string from this variable and call your function $scrambled_url = someFunction(-matches[0]) . After that you can call the replace function with this $scrambled_url like in my comment above.

Ash · Accepted Answer · 2020-05-08 00:56:52Z

Regex

(?<=img src=\\\").+?(?=\\)

(?<=img src=\\\") # Finds `img src=\` escaping `\` and `"`  
.+?               # Everything between the two outer capture groups  
(?=\\)            # To the next backslash, again escaping the `\`

If you want to capture the url first to do other stuff with it, you can create a new regex object to check your matches.

$obj = # Import your text here how you like
$regex = [regex]::new('(?<=img src=\\\").+?(?=\\)')
$matches = $regex.Matches($obj)

You could create new variables for what you want to change the path to and then use the matches to replace the text. Adding a scramble function.

function Scramble {
    Param(
        [parameter(ValueFromPipeline=$true)][string]$InputObject
    )

    $split = $InputObject -split "/" | Select-Object -Skip 1
    return "/" + (($split | Get-Random -Count $split.Count) -join "/")
}

foreach ($match in $matches) {
    $obj.Replace($match.Value, ($match.Value | Scramble))  # .Net Method here to replace the specific string found. No need for another regex.
}

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