Loop over array

Question

I need a piece of powershell-code to search and replace a certain string inside a text-file. In my example, I want to replace 23-06-2016' with '24-06-2016'. The script below does this job:

$original_file  = 'file.old'
$destination_file   = 'file.new'

(Get-Content $original_file) | Foreach-Object {
$_ -replace '23-06-2016', '24-06-2016' `
} | Out-File -encoding default $destination_file

As the search / replace string change I want to loop over an array of dates which might look like this:

$dates = @("23-06-2016","24-06-2016","27-06-2016")

I tried use the

$original_file  = 'file.old'
$destination_file   = 'file.new'

foreach ($date in $dates) {
  (Get-Content $original_file) | Foreach-Object {
  $_ -replace 'date', 'date++' `
  } | Out-File -encoding default $destination_file
}

In a first step, the date '23-06-2016' should be replaced by '24-06-2016' and in a second step, the date '24-06-2016' should be replaced by '27-06-2016'.

As my script is not working I am seeking for some advice.

briantist · Accepted Answer · 2016-10-12 14:58:57Z

9

You are using $date as your instance variable in your foreach loop but then referencing it as 'date', which is just a string. Even if you used '$date' it would not work because single-quoted strings do not expand variables.

Further, $date is not a number, so date++ would not do anything even it were referenced as a variable $date++. Further still, $var++ returns the original value before incrementing, so you would be referencing the same date (as opposed to the prefix version ++$var).

In a foreach loop, it's not very practical to refer to other elements, in most cases.

Instead, you could use a for loop:

for ($i = 0; $i -lt $dates.Count ; $i++) {
    $find = $dates[$i]
    $rep = $dates[$i+1]
}

This isn't necessarily the most clear way to do it.

You might be better off with a [hashtable] that uses the date to find as a key, and the replacement date as the value. Sure, you'd be duplicating some dates as value and key, but I think I'd rather have the clarity:

$dates = @{
    "23-06-2016" = "24-06-2016"
    "24-06-2016" = "27-06-2016"
}

foreach ($pair in $dates.GetEnumerator()) {
    (Get-Content $original_file) | Foreach-Object {
      $_ -replace $pair.Key, $pair.Value
    } | Out-File -encoding default $destination_file
}

edited Oct 12, 2016 at 14:58

answered Oct 12, 2016 at 14:15

briantist

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2 Comments

Phil U. Over a year ago

Thanks you @braintist! There is only some minor error in your definiton of $dates, I guess a semicolon instead of a comma should be used to seperate the pairs from each other: $dates = @{ "23-06-2016" = "24-06-2016"; "24-06-2016" = "27-06-2016" }

briantist Over a year ago

@PhilU. whoops, yeah, I updated. In fact when you put them on separate lines as I have, no other separator is needed. If you put key/value pairs on the same line as others, then a semi-colon is used. Good catch!

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