Use regular expression and parse the year and month from the file name.

$filename =~ /^(\d+)-(\d+)-(.*)/;
my $year = $1;
my $mon = $2;

print("$year-$mon");
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Use split() method

my $filename = "2010-7-this-is-an.html";
my ($year, $mon) = split('-', $filename);
print("$year-$mon");
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