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<?php $strings = [ 'dir1summary', 'dir10summary', 'dir1summarydue', 'dir10summarydue', 'directive1', 'directive10', 'directivecode1', 'directivecode10', ]; var_export(preg_replace_callback('/dir(?:ective)?(\D*)(\d+)(.*)/', function ($m) { return "directive{$m[1]}{$m[3]}" . str_pad($m[2], 2, "0", STR_PAD_LEFT); }, $strings));
Output for 7.2.0 - 7.2.33, 7.3.0 - 7.3.33, 7.4.0 - 7.4.33, 8.0.0 - 8.0.30, 8.1.0 - 8.1.33, 8.2.0 - 8.2.29, 8.3.0 - 8.3.25, 8.4.1 - 8.4.12
array ( 0 => 'directivesummary01', 1 => 'directivesummary10', 2 => 'directivesummarydue01', 3 => 'directivesummarydue10', 4 => 'directive01', 5 => 'directive10', 6 => 'directivecode01', 7 => 'directivecode10', )

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