PHP REGEX: how to pad numbers in the middle/end of a string

WhiteRau :

i have a list of key=>value pairs from a JSON squirt. i sorted the array and i'm left with the following (excerpted relevant cases because they go as high as 92):

dir1summary
dir10summary
dir1summarydue
dir10summarydue
directive1
directive10
directivecode1
directivecode10

what i need to do is: 1) place all the digits at the end and 2) pad them to 2 digits (01,02,&c) so the list ends up looking like this:

directivesummary01
directivesummary10
directivesummarydue01
directivesummarydue10
directive01
directive10
directivecode01
directivecode10

i was hoping to do this with one REGEX statement given the obvious similarity in key names, but i got lost. here's what i have so far:

dir((\d{1,2}(summary|summarydue))|((ective\d{1,2})|(ectivecode\d{1,2})))

...aaaand i'm lost what to do next. how to move on? is there a better compact way to do this?

EDIT: this also means i have to replace 'dir' with 'directive'. it's implied in the result list, but i didnt' make a bullet item for it. also, the REGEX is all i was able to build at RegExer. thus the "lost what to do next" part.

mickmackusa :

• Match but don't capture dir
• Match but don't capture the optional substring ective
• Retain zero or more non-digital characters immediately after ective as capture group #1 (this accounts for optional substrings like summarydue)
• Retain the whole integer as capture group #2

• Retain the remainder of the string as capture group #3

  ---

• In the custom function, hardcode directive, then append capture group #1 (which may be empty), then capture group #3 (might also be empty), finally left pad capture group #2 with a zero to a maximum length of 2-digits and append that value to the end of the string

Code: (Demo)

$strings = [
    'dir1summary',
    'dir10summary',
    'dir1summarydue',
    'dir10summarydue',
    'directive1',
    'directive10',
    'directivecode1',
    'directivecode10',
];

var_export(
    preg_replace_callback(
        '/dir(?:ective)?(\D*)(\d+)(.*)/',
        function ($m) {
            return "directive{$m[1]}{$m[3]}" . str_pad($m[2], 2, "0", STR_PAD_LEFT);
        },
        $strings
    )
);

Output:

array (
  0 => 'directivesummary01',
  1 => 'directivesummary10',
  2 => 'directivesummarydue01',
  3 => 'directivesummarydue10',
  4 => 'directive01',
  5 => 'directive10',
  6 => 'directivecode01',
  7 => 'directivecode10',
)