How to replace dates in text file with Powershell using regular expressions

Question

I've done much searching on this and haven't worked out the answer, but I feel like I am close!

I have dates in a text file in the following format: 18/06/2012 23:00:43 (dd/mm/yyyy HH:MM:SS) which I want to convert to: 2012-18-06 23:00:43 (yyyy-dd-mm HH:MM:SS) using Powershell.

To perform the conversion in a text editor using regular expressions I would do this:

Find: ([0-9]+)/+([0-9]+)/+([0-9]+)

Replace with: \3-\2-\1

So I have tried using this same logic in a the following Powershell script:

(Get-Content C:\script\test.txt) | 
Foreach-Object {$_ -replace "([0-9]+)/+([0-9]+)/+([0-9]+)", "(\3-\2-\1)"} | 
Set-Content C:\script\test.txt

but that results in the following undesired change:

\3-\2-\1 23:00:43

Can anybody help me nail this?

Many thanks in advance!

If you have a date string in some variable ($date) then to reformat it easily in powershell: (Get-Date $date).ToString('yyyy-dd-MM HH:mm:ss') — EBGreen
– EBGreen, Commented Jan 31, 2018 at 17:19

Michael Myers · Accepted Answer · 2012-06-20 15:35:55Z

22

This is what you want:

(Get-Content C:\script\test.txt) | 
Foreach-Object {$_ -replace "([0-9]+)/+([0-9]+)/+([0-9]+)", '$3-$2-$1'} | 
Set-Content C:\script\test.txt

Capturing group references are done with the $ symbol, not a backslash. Also, to reference a captured group by number, you must use single quotes around the replacement string; otherwise, PowerShell will interpret any $ symbol as a reference to a previously defined variable, which in this case will result in the string "--" since no such variables exist.

answered Jun 20, 2012 at 15:35

Michael Myers♦

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3 Comments

AshBestos Over a year ago

Thanks Michael, but unfortunately I am still getting the result: \3-\2-\1 23:00:43 with this script. Am I missing something?

Michael Myers Over a year ago

@AshBestos: Did you remember to save your script after copying this in? That's my first guess.

AshBestos Over a year ago

Aha, I was actually checking a file called text.txt in a different directory! Oops! Thanks very much for your help.

Akim · Accepted Answer · 2012-06-20 15:36:46Z

4

The -replace operator supports the same replacement text placeholders as the Regex.Replace() function in .NET. E.g. $& is the overall regex match, $1 is the text matched by the first capturing group, and ${name} is the text matched by the named group "name".

Instead of "(\3-\2-\1)" use '($3-$2-$1)'

'06/18/2012 23:00:43' -replace "(\d+)/(\d+)/(\d+)", '($3-$2-$1)'

answered Jun 20, 2012 at 15:36

Akim

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Comments

CB. · Accepted Answer · 2012-06-20 15:36:45Z

2

try

Foreach-Object {$_-replace "([0-9]+)/+([0-9]+)/+([0-9]+)", '$3-$2-$1'}

answered Jun 20, 2012 at 15:36

CB.

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