diff --git a/shiftPres.php b/shiftPres.php
new file mode 100644
index 0000000..2ce3022
--- /dev/null
+++ b/shiftPres.php
@@ -0,0 +1,126 @@
+<?php
+
+// Print error message and exit
+function printStderr($msg) {
+    error_log($msg);
+    exit(-1);
+}
+
+class ShiftPres {
+    // For German date matching
+    const  PREG = '/^(0[1-9]|[12][0-9]|3[01])\.(0[1-9]|1[0-2])\.([1-9]\d{3})$/';
+    // Read "past.md" and "vor.md" into instance arrays and set up new vor.txt
+    public function __construct($vor='vor.md', $past='past.md') {
+        $this->CET = new DateTimeZone('Europe/Berlin');
+        $this->vor = $vor;
+        $this->vorMd = file($vor, FILE_IGNORE_NEW_LINES);
+        $vorBase = basename($vor, '.md');
+        $this->vorT = $vorBase . '.txt';
+        $this->vorTxt = [];
+        $this->pastT = $past;
+        $this->pastMd = file($this->pastT, FILE_IGNORE_NEW_LINES);
+        $this->exit = 0; // Default return value
+    }
+
+    // Save "vor.txt" and "past.md"  before leaving
+    public function save() {
+        // Backup files first
+        copy($this->vorT, $this->vorT . '.bak');
+        copy($this->pastT, $this->pastT . '.bak');
+        file_put_contents($this->vorT, implode(PHP_EOL, $this->vorTxt) . PHP_EOL);
+        file_put_contents($this->pastT, implode(PHP_EOL, $this->pastMd) . PHP_EOL);
+        // Signal to calling bash script to put files into git
+        $this->exit = 1;
+    }
+
+    // Shift from "vor.md" to "past.md", creating "vor.txt" along the way
+    public function shift() {
+        $yester = (new DateTime('now', $this->CET))->modify('- 1 day');
+        $yester->setTime(0, 0);
+        // For correct insertion into past array
+        $past = $this->findPast();
+        if ($past < 0) {
+            printStderr("Can't locate insert position in $this->pastT, exiting");
+        }
+
+        // Loop through "vor.md" and check if yesterday is 4th Tuesday => shift to "past.md"
+        // Otherwise copy to "vor.txt", including custom date if found (as in: not 4th Tuesday)
+        foreach ($this->vorMd as $line) {
+            $fields = array_filter(explode('|', $line));
+            $ff = explode(', ', $fields[1]);
+            // Does 1st field contain date?
+            if (count($ff) > 1) {
+                $dat = trim($ff[1]);
+                // If so, in valid format
+                if (preg_match(self::PREG, $dat)) {
+                    $dp = new DateTime($dat, $this->CET);
+                    $dp->setTime(0, 0);
+                    // if we are not invoked on the morning of the 4th Wednesday, copy to "vor.txt"
+                    if ($dp != $yester) {
+                        // If manually set date doesn't equal fourth Tuesday, copy
+                        if ($dp != $this->get4Tuesday($dat)) {
+                            $str0 = '|' . implode($fields, '|') . '|';
+                        } else {
+                            // Otherwise, only copy text
+                            $str0 = '|' . implode(array_slice($fields, 1), '|') . '|';
+                        }
+                        $this->vorTxt[] = $str0;
+                    } else {
+                        // Shift to "past.md"
+                        array_splice($this->pastMd, $past, 0, $line);
+                    }
+                }
+            }
+        }
+    }
+
+    // Check if "vor.txt" and "past.md" need to be saved (length of "vor.md" and "vor.txt" differ => line shifted)
+    public  function checkSave() {
+        // Take header of "vor.md" into account
+        return count($this->vorTxt) != count($this->vorMd)-2;
+    }
+
+    public function getExit() {
+        return $this->exit;
+    }
+
+    // Find first entry in PAST
+    private function findPast() {
+        for ($i = 0; $i < count($this->pastMd); $i++) {
+            $fields = array_filter(explode('|', $this->pastMd[$i]));
+            $ff = explode(', ', $fields[1]);
+            if (count($ff) > 1) {
+                $dat = trim($ff[1]);
+                if (preg_match(self::PREG, $dat)) {
+                    return $i;
+                }
+            }
+        }
+        return -1;
+    }
+    
+    private function get4Tuesday($dat) {
+        // This is for PHP >= 8.1 as the old strftime will be deprecated by then, so use datefmt_format_object if we are running on PHP beyond version 7
+        $date_time = new DateTime($dat, $this->CET);
+        $first_day = $date_time->modify('first day of this month');
+        $ts = $first_day->getTimeStamp();
+        if (intval(explode(".", phpversion())[0]) >= 7) {
+            $date_time->setTimestamp(strtotime('fourth tuesday of this month', $ts));
+            $tuesday = datefmt_format_object($date_time, 'd.M.yyyy ', 'de_DE.utf8');
+        } else {
+            $tuesday = strftime('%d.%m.%Y ', strtotime('fourth tuesday of this month', $ts));
+        }
+        return new DateTime($tuesday);
+    }
+}
+
+setlocale(LC_TIME, 'de_DE.utf8');
+date_default_timezone_set('Europe/Berlin');
+$shift = new ShiftPres();
+$shift->shift();
+if ($shift->checkSave()) {
+    $shift->save();
+}
+// Signal to calling bash script
+exit($shift->getExit());
+?>