Replace characters with incrementing value

Question

I'm trying to figure out how to replace a certain string that repeats itself multiple time in a txt file with an incrementing value.

What I try to achieve is the following:

I have multiple HTML links in a table, each of the links have the exact same ending i.e.: XYZ

I want to change XYZ to 1, 2, 3, 4, 5 and so on... using PowerShell.

(Get-Content c:\temp\test.txt).replace('XYZ', 'MyValue') |
    Set-Content c:\temp\test.txt

It is the 'MyValue' part of using an incrementing number for each replacement I'm not sure how to achieve it.

Robert Dyjas · Answer 1 · 2018-08-06T14:56:24.513

3

Hint: be aware of using Get-Content | .... | Set-Content to the same file due to possible data loss! It doesn't apply to reading file in a subexpression/grouping expression as you did, but be aware of it in the future (as a best practice). Credits to @Ansgar Wiechers for clarification.

Solution:

You can define callback function to [Regex]::Replace (String, String, MatchEvaluator) method:

$global:counter = 0
$content = (Get-Content c:\temp\test.txt)

# Below can be used to verify it's working correctly instead of creating a file
# $content = "aXYZ","bXYZ","cXYZ","dXYZ","eXYZ"

$content | % {[Regex]::Replace($_, 'XYZ', {return $global:counter += 1}) } | Set-Content c:\temp\test.txt

Output will be:

a1
b2
c3
d4
e5

Explanation:

The parameters you pass to Replace are as follows:

The string to search for a match.
The regular expression pattern to match.
A custom method that examines each match and returns either the original matched string or a replacement string.

The custom method increments the counter each time the regex is matched. Unfortunately, for some reason, it requires you to use global variable scope which is in general not the best practice if not needed (as mentioned by @Paxz in the comments).

As @TessellatingHeckler found out, the first version of solution used Replace on $content variable which resulted in removing all newlines. You have to use Foreach-Object (or % as its alias) to do the replacing in each single line.

edited Aug 06 '18 at 14:56

answered Aug 06 '18 at 13:25

Robert Dyjas

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The same can be achieved without the `global` scope. Using a global scope, where it is not explicit needed is a bad practice. – Paxz Aug 06 '18 at 13:32
Thanks for your comment @Paxz! Yea, I know that we should avoid that but I wasn't able (yet) to achieve that without it this time. Can you suggest? – Robert Dyjas Aug 06 '18 at 13:38
1

Yeah I tested it wrong, seems like i really needs another scope (that kinda makes me sad...). – Paxz Aug 06 '18 at 13:44
1

Incorrect output, you've implicitly joined all the lines with a space into one string. Now the file has no newlines. – TessellatingHeckler Aug 06 '18 at 14:15
Nice catch, fixed. – Robert Dyjas Aug 06 '18 at 14:24
Okay, I'm in love with this community wow. Thank you so much for curing my headache I was having with this ! – Alex Pelletier Aug 06 '18 at 14:44
1

You're welcome! Please remember to mark the answer which helped you as accepted (see [What should I do when someone answers my question?](https://stackoverflow.com/help/someone-answers). – Robert Dyjas Aug 06 '18 at 14:46
1

Writing to the same file is not an issue if you read the file in a subexpression/grouping expression as the OP does. – Ansgar Wiechers Aug 06 '18 at 14:50
Thx @AnsgarWiechers, clarified in my answer! – Robert Dyjas Aug 06 '18 at 14:56

score 1 · Answer 2 · answered Aug 06 '18 at 13:45

Same as @robdy answer, but without the global scope refference:

# Simulation of Get-Content
$content = "aXYZ","bXYZ","cXYZ","dXYZ","eXYZ"

$i = 0
$result = $content.ForEach({
    $i++
    $_ -replace 'XYZ', $i
})

$result | Out-File -FilePath "$env:TEMP\test.txt" -Encoding utf8 -NoClobber

We're basically looping over the content of the file and replace the string XYZ with the number. Then we save that in to a new variable, which is later used to write the new content to the file.

Replace characters with incrementing value

2 Answers2