Add use warnings; use strict; to the start of your code. After you have resolved the errors that that generates, and if you still have a problem, ask the question again with the modified code.

My guess is that $tier and $code1 are going out of scope so when you get to the assignment new variables are created and have undefined values.

Note that in addition to the scoping problem if($code1 = 0) should probably be if($code1 == 0). For purposes of testing a value for @contents would be nice. _$tier_$code has to be written _${tier}_$code or Perl will think the variable is %tier_.

Note that in addition to the scoping problem if($code1 = 0) should probably be if($code1 == 0).

Curiously enough this node (in an interesting thread) about mistyping = for == in if clauses was cited a few hours before.

IMHO both variations suffer from escapism.

When I have to insert double quotes into a double quoted string, I will most likely use qq for better readability:

my $message = qq(<event id="ALERT_${tier}_$code1" source="APP">);

YMMV

I often like using sprintf for it instead of variable concatentation .. note also using single quotes for the string literals means you don't have to have the escaping backslashes...

my $message = sprintf '<event_id="ALTER_%d_%d" source="APP">', $tier, 
+$code1;
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Also, to OP: I second blazar's comments, and would also add to them that your assignment of $severity with the two if statements can simply be written as:

$severity = $code1 ? 1 : 5;
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Though, what's the point of $severity ? It doesn't seem to be used...

Even if you found a fix that seems to make it work, do not ignore the good advices GrandFather (and others) gave you. To add to them:

my $temp;
my $code;
my $info;
my $count = 0;
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Generally variables should be declared in the innermost lexical scope in which they're actually needed rather than all at the top.

my $length = scalar@contents;
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no need for that explicit scalar. And as a matter of style, Perl is a free form language: try to adjust whitespace to improve readability. (Or to degrade it - but only if you're playing obfu!)

for(my $i=0;$i<=$length;$i++) {
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As a general rule, there are situations in which C-style for loops are preferrable. But they're rare! more commonly it is recommendable to use Perl-style ones, and in particular in this case I don't see what the former buys you over the latter.

                if($temp == 1) {
                        $tier = "WEB";
                }
                if($temp == 2) {
                        $tier = "APP";
                }
                if($temp == 3) {
                        $tier = "DB";
                }
                if($code1 != 0) {
                        $severity = 1;
                }
                if($code1 = 0) {
                        $severity = 5;
                }
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These smell like you may save some complexity and use a hash instead. That would make the code more maintainable as well: you'd just have to add/remove/modify keys accordingly.