my $text;
{
    local $/ = undef;
    $text = <DATA>;  #"slurp" the whole file
}


while ($text =~ / 
         (\d+) 
          \. 
          pace 
          (.*?)
          \d+
          \.
          slow  
                /xmsg ) 
{
    print "filename=$1 and text=$2";
}

    
__DATA__
12345.pace
text1
12345.slow
123456.pace
text2
123456.slow
hyds.pace
bla bla bla
uiw.slow



--output:--
filename=12345 and text=
text1
filename=123456 and text=
text2