Convert the back slashes to forward slashes to help Perl interpret the path. Put backtics around the commands you want to execute. The output of the command will be returned.

my @MEDIA;
for (`C:/Program Files/Veritas/Netbackup/bin/admincmd>bpimagelist -A -
+media -hoursago 24`) {
  s/\|/ /; 
  my ($Image) = split;
  for (`C:/Program Files/Veritas/Netbackup/bin/admincmd>nbemmcmd -list
+media -mediaid $Image`) {
    next unless m/Media ID|Data Expiration/i; 
    push @Media, $_;
  }
}
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Consolidate that last for loop:

push @Media, grep { ! /Media ID|Data Expiration/i }  `C:/Program Files
+ ...`;
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