Lhamo_rin, i don't know what you are really going to achieve, but as per your input and output, i assume, you can accomplish using regex as shown below.

$filename = 'FileName'; #any filename
$string = 'FileName.089-09_08_45';
$string =~ s/^$filename\.(\d{2})\d/$1/;
print $string;

output:
08-09_08_45
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