In preparation of trying to suggest a replacement for your switch use i would like to start with this comment

$t[++$#t]=threads->new(\&adminpass); seems to be a real verbose way of saying push @t,threads->new(\&adminpass);

It looks like your use of switch is to process a comma separated list of commands. a simple replacement for

   switch($action) {
      case /adminpass(,|$)/ {
         print "Do adminpass ($hostname)\n" if($verbose || $debug);
         $t[++$#t]=threads->new(\&adminpass);
         next;
      } # end case /adminpass/
      case /backup(,|$)/ {
         print "Do backup ($hostname)\n" if($verbose || $debug);
         $t[++$#t]=threads->new(\&backup);
         next;
      } # end case /backup/
      case /buildhosts(,|$)/ {
         print "Do buildhosts ($hostname)\n" if($verbose || $debug);
         $t[++$#t]=threads->new(\&buildhosts);
         next;
      } # end case /buildhosts/
      case /buildhostsdell(,|$)/ {
         print "Do buildhostsdell ($hostname)\n" if($verbose || $debug
+);
         $t[++$#t]=threads->new(\&buildhostsdell);
         next;
      } # end case /buildhostsdell/
...
}
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might be

      if ($action=~/adminpass(,|$)/) {
         print "Do adminpass ($hostname)\n" if($verbose || $debug);
         push @t,threads->new(\&adminpass);
      } # end case /adminpass/
      if ($action=~/backup(,|$)/) {
         print "Do backup ($hostname)\n" if($verbose || $debug);
         push @t,threads->new(\&backup);
      } # end case /backup/
      if ($action=~/buildhosts(,|$)/) {
         print "Do buildhosts ($hostname)\n" if($verbose || $debug);
         push @t,threads->new(\&buildhosts);
      } # end case /buildhosts/
      if ($action=~/buildhostsdell(,|$)/) {
         print "Do buildhostsdell ($hostname)\n" if($verbose || $debug
+);
         push @t,threads->new(\&buildhostsdell);
      } # end case /buildhostsdell/
...
[download]

but a more efficient and direct solution may be as follows

 
# create a list of the command names and the subroutines they call 
my %cmds=(adminpass      =>\&adminpass,
          backup         =>\&backup,
          buildhosts     =>\&buildhosts,
          buildhostsdell =>\&buildhostsdell
          ); 
# break list of comma sep commands into words 
#  and if we have a subroutine for that word start a thread with it  
for my $cmd (split(',',$action)) { 
      if (exists $cmds{$cmd}) { 
         print "Do $cmd ($hostname)\n" if($verbose || $debug);
         push @t,threads->new($cmds{$cmd});
      } 
      else { 
        print "Command $cmd unknown\n"; 
      } 
}
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