Select Code to Download

/(?<=_)00001(?=[.]\w+$)/

rand(9999999)+1

s/(?<=_)00001(?=[.]\w+$)/sprintf "%07d" => rand(9999999)+1/e

$ perl -Mstrict -Mwarnings -le '
    my @test_filenames = qw{
...
        print;
    }
'

XYZ12345_X05_20110805_9999999_00000.TXT
XYZ12345_X05_20110805_9999999_1656320.TXT
...
XYZ12345_X05_20110805_9999999_00001x.TXT
XYZ12345_X05_20110805_00001_0901076.TXT
XYZ12345_X05_20110805_00001_00001xxx.TXT