my $emd = `date --date '-30 min' +'%H'`;
chop ($emd);

$emd = "/tmp/pathtomyfiles/$emd.txt";
[download]

Probably better to avoid shelling out to /bin/date and use the core POSIX::strftime instead. Also, chomp would be better than chop in your original code.

johngg@shiraz:~/perl/utils > perl -Mstrict -Mwarnings -MPOSIX=strftime
+ -E '
my $emd = strftime q{/tmp/pathtomyfiles/%H.txt},
   localtime( time() - 1800 );
say $emd;'
/tmp/pathtomyfiles/10.txt
[download]

I hope this is of interest.