my ($LSV, $LSN) = $BE_temp =~ m/^\|\s(\w+_\d+)\s+\|\s+(\w+)\s+\|$/m;
if ( $LSV =~ m/dsmgt_03_03/ ) { ... }

If the initial match against  $BE_temp fails, the subsequent match against  $LSV will produce a "Use of uninitialized value $LSV in pattern match ..." warning (not error) because  $LSV et al are undefined. The initial match should be tested in some way and subsequent matches (or uses of the extracted strings) made dependent on a successful initial match, e.g.:

if (my ($LSV, $LSN) = $BE_temp =~ m/^\|\s(\w+_\d+)\s+\|\s+(\w+)\s+\|$/
+m) {
    do_something_with($LSV);
    do_something_with($LSN);
    }
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