PS function to populate IDs to URI

Question

I have the following string

$list = @("123","456","789")
$template = "https://mysite.test/api/v1/policy/{id}/version/{id}/example"

I am working on a function to meet the following requirements :

• replaces each {id} in the order provided by an array ($list)
• If the array list contains exactly one more item than the count of {id} append the last id at the end of the $string (in this example, array contains 3 items, string will be appended by /789)
• accepts an array of $ids but fails if array list does not match list of {id} or list of array +1 (for the above append scenario)

The issue is that every {id} is replaced by the first item from my list, as shown below

if ($template.Contains('{id}')) {
    foreach ($id in $list ) {
        $template = $template -replace '{id}', $id 
    }
}

$string
https://mysite.test/api/v1/policy/123/version/123/example

Expected values

• array with 2 values

    https://mysite.test/api/v1/policy/123/version/456/example
  

• array with 3 values

    https://mysite.test/api/v1/policy/123/version/456/example/789
  

Answer 1

The easiest option is to use format string instead of {id} for interpolating the values:

$template = 'https://mysite.test/api/v1/policy/{0}/version/{1}/example{2}'
$list = @('123', '456', '789')

if ($list.Count -lt 3) {
    $list += $null
}
else {
    $list[2] = '/' + $list[2] # prepend `/` to the last item
}

$template -f $list

If you must use {id} then, perhaps using regex replacement with a match evaluator or replacement with a scriptblock work for this use case. Basically, in the evaluator you can increment an index for each pattern match and get the next replacement value in $list.

It would look something like this for PowerShell 5.1:

$template = 'https://mysite.test/api/v1/policy/{id}/version/{id}/example'
$list = @('123', '456', '789')
$idx = @(0)

[regex]::Replace($template, '{id}|$', {
    # if there is a "next value" in the list
    if ($next = $list[$idx[0]++]) {
        # if matching EOL
        if (-not $args[0].Value) {
            return '/' + $next
        }
        # else
        $next
    }
})

And like this for PowerShell 7+:

$template = 'https://mysite.test/api/v1/policy/{id}/version/{id}/example'
$list = @('123', '456', '789')
$idx = @(0)

$template -replace '{id}|$', {
    # if there is a "next value" in the list
    if ($next = $list[$idx[0]++]) {
        # if matching EOL
        if (-not $_.Value) {
            return '/' + $next
        }
        # else
        $next
    }
}