Powershell - Replace first occurrences of String

Question

I've searched for a fair amount for the answer but all I get is how I do it with multiple Strings. I'm pretty new to PowerShell but want to know how I can manage to do it.

I simply want to remplace the first occurence of "1" with "2" ... I only can close to it but no more. The code I found was:

Get-ChildItem "C:\TEST\1.etxt" | foreach {
$Content = Get-Content $_.fullname
$Content = foreach { $Conten -replace "1","2" }
Set-Content $_.fullname $Content -Force
}

The content of the txt is just random: 1 1 1 3 3 1 3 1 3 ... for keeping it simple.

Could someone please explain how I do it with the first occurence and if it is possible and not to time consuming how I can replace for example the 3rd occurrence?

DarkLite1 · Accepted Answer · 2016-06-30 14:24:22Z

6

Same answer as Martin but a bit more simplified so you might better understand it:

$R=[Regex]'1'
#R=[Regex]'What to replace'

$R.Replace('1 1 1 3 3 1 3 1 3','2',1)
#R.Replace('Oringinal string', 'Char you replace it with', 'How many')

#Result = '2 1 1 3 3 1 3 1 3'

If you want this in a one-liner:

([Regex]'1').Replace('1 1 1 3 3 1 3 1 3','2',1)

Found this information here.

edited Jun 30, 2016 at 14:24

answered Jun 30, 2016 at 14:15

DarkLite1

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1 Comment

Illuvar Over a year ago

Wow, thanks. That I got without thinking to hard. :)

Martin Brandl · Accepted Answer · 2016-06-30 13:31:48Z

1

You could use a positive lookahead to find the position of the first 1 and capture everything behind. Then you replace the 1 with 2 and the rest of the string using the capture group $1:

"1 1 1 3 3 1 3 1 3" -replace '(?=1)1(.*)', '2$1'

Output:

2  1 1 3 3 1 3 1 3

To caputre the third occurence, you could do something like this:

"1 1 1 3 3 1 3 1 3" -replace '(.*?1.*?1.*?)1(.*)', '${1}2$2'

Output:

1 1 2 3 3 1 3 1 3

edited Jun 30, 2016 at 13:31

answered Jun 30, 2016 at 13:13

Martin Brandl

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1 Comment

Illuvar Over a year ago

It does work. Now I just have to find out what exactly every stept does, but I think I will figure out that myself with some research. Thanks you for your response. :)

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