A quick hack to find all of the unique token abbreviations, construct a regex, and report the matching tokens.

#!/usr/bin/env perl
use strict;
use warnings;

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

for my $token (@tokens) {
    if (1 == grep /^$token/, @tokens) {
        push @abbrev, $token;
    } else {
        die "Error: $token is not unique in list of tokens\n";
    }

    # Generate abbreviations that match only one token
    my $abbrev = $token;
    while (1) {
        chop($abbrev);
        last unless (1 == grep /^$abbrev/, @tokens);
        push @abbrev, $abbrev;
    }
}

# Show the abbreviations
print "Abbreviations = (" . join(',', sort @abbrev) . ")\n";

# Create the regex string to use
my $regex = join('|', sort @abbrev);
print "Token regex = \"$regex\"\n\n";

# Read the file and output tokens

while (<>) {
    my $match;
    if (($match) = m/^($regex)$/) {
        my @matches = grep /^$match/, @tokens;
        print "$match matched for @matches on line $.\n";
    }
}

exit;
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Input file:

report_t
  14:09:33 PDT
report_d
Fri Jun 12 2015

res
Resetting the time

report_time
  00:00:00
[download]

Output:

Abbreviations = (rea,read,report_d,report_da,report_day,report_t,repor
+t_ti,report_tim,report_time,res,rese,reset)
Token regex = "rea|read|report_d|report_da|report_day|report_t|report_
+ti|report_tim|report_time|res|rese|reset"

report_t matched for report_time on line 1
report_d matched for report_day on line 3
res matched for reset on line 6
report_time matched for report_time on line 9
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There's probably a module or two that will do this for you, but I didn't bother to look for it.

Edit to add:

I also thought of creating regex expressions, as above, but with a single subexpression per unique token. For report_time, the regex is:

m/^report_t(?:i(?:m(?:e)?)?)?/
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It's a bit more complicated to do this than the above script's method. For a small list of @tokens, it makes little difference. For huge lists, it's probably better to put the original pipecleaner version through an optimizer, which will be somewhat better than this head-scratching fingernails version.