I found 4 problems with your code:
2 syntax errors
1 logical error
1 formatting for this site error

syntax error #1:
you have

push @{$p2i{sp}}, $ipr;  # $ missing for key reference
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when you should have

push @{$p2i{$sp}}, $ipr;
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syntax error #2:
you have

print "$key\t$p2i{$key}\n";
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when you should have

print "$key\t@ {$p2i{$key} }\n";  # need @ to dereference array
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logical error #1:
your use of uc() for key lookups will return nothing because the hash keys, as entered from the text file, are all lowercase (at least in the sample you provided).

formatting error #1:
you have

if (exists $p2i{$user}) {
        print "$user is in the hash. \n";if (exists $p2i{$user}) {
        print "$user is in the hash. \n";
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when you should have

if (exists $p2i{$user}) {
        print "$user is in the hash. \n";
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I corrected the above and the code ran fine

hope this helps,
davidj