$ perl -wE'
$s = q{anfang <?php
echo get_pfad();
?> ende};
$s =~ s/(<\?php.*?\?>)/ /gsi;
say $s;'
anfang   ende

$ perl -wE'
$s = q{anfang <?php echo "Aktualisierung am ".date("d.m.Y",filemtime(basename($_SERVER["PHP_SELF"]))); ?> ende};
$s =~ s/(<\?php.*?\?>)/ /gsi;
say $s;' 
anfang   ende