On the other hand, maybe you wanted a hash with all the valid unique prefixes of @tokens, like this:

#!/usr/bin/perl

# http://perlmonks.org/?node_id=1130246

use strict;
use warnings;

my @tokens = qw/report_time report_day reset read/;

my %valid;    # generate hash with valid unique matches
/^(.+)(??{$valid{$1}++})^/ for @tokens;
delete @valid{grep $valid{$_} > 1, keys %valid};

/^(\w+)/ and $valid{$1} and print "$1\n" while <DATA>;

__DATA__
report_t
  14:09:33 PDT
report_d
Fri Jun 12 2015
report (should not show up)

res
Resetting the time

report_time
  00:00:00

rea foo.bar
Info: reading file foo.bar
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