#!/bin/perl -w
...
@sysFile1 = (a_b, a_c, a_d);
@sysFile2 = (a_c, a_e, b_f);

foreach $line1 (@sysFile1){
     trim(\$line1);
     (my $tmp1, my $tmp2) = split/_/, $line1;
     foreach $line2 (@sysFile2) {
          trim(\$line2);
          (my $tmp3, my $tmp4) = split/_/,$line2;
          if (($tmp1 eq $ $tmp3) && ($tmp2 eq $tmp4)) {
               print "found\n";
          } else {
               print "not found\n";
          }
          delete $sysFile1[1];
     }
}

$ test.pl
delete argument is not a HASH element or slice at test.pl line 50

$ cat del.pl
#! /usr/local/bin/perl -w

print "perl version is ", $],  "\n";

@array=(a_b, a_c, a_d);

for ($index=0; $index <= $#array; $index++) {
        if (exists $array[$index])  {
                print "index = ", $index, "  element = ", $array[$index], "\n";
        } else {
                print "index = ", $index, "  element is not there", "\n";
        }
}

delete $array[1];

for ($index=0; $index <= $#array; $index++) {
        if (exists $array[$index])  {
                print "index = ", $index, "  element = ", $array[$index], "\n";
        } else {
                print "index = ", $index, "  element is not there", "\n";
        }

}

$ ./del.pl
perl version is 5.006001
index = 0  element = a_b
index = 1  element = a_c
index = 2  element = a_d
index = 0  element = a_b
index = 1  element is not there
index = 2  element = a_d
$

[bernardchan@bernardchan ~]$ perl -MData::Dumper -w -e '@a = (1,2,3); delete $a[0]; print Dumper [@a]'
$VAR1 = [
          undef,
          2,
          3
        ];
[bernardchan@bernardchan ~]$ perl -MData::Dumper -w -e '@a = (1,2,3); splice(@a, 0, 1); print Dumper [@a]'
$VAR1 = [
          2,
          3
        ];