The approach does depend on how your input data varies, but the below will work for your example. 
use strict;
use warnings;

for my $line (<DATA>) {
    print $line if $line =~ /^\d{2}-\d{2}-\d{4}\s/;
}

__END__
03-15-2021-1 21.1.0-s103 2021/03/15:14:16:39 21.1 21.10-s103
03-15-2021-2 21.1.0-s103 2021/03/15:14:16:39 21.1 21.10-s103
03-15-2021 21.1.0-s102 2021/03/15:04:00:09 21.1 21.10-s102

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In reply to Re: grep only lines having matched pattern by philipbailey
in thread grep only lines having matched pattern by noviceuser

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