File LeadingDistinct.pm:

# LeadingDistinct.pm                                        15jun15waw

# for each token in a set of tokens, find minimum leading
# substring that uniquely distinguishes the token
# from all other tokens in the set.

# works with Perl 5.8.9

package LeadingDistinct;

use warnings;
use strict;

use List::Util       qw(max);
use List::MoreUtils  qw(uniq);


sub extract {

    my (@tokens,
        ) = @_;

    @tokens = ('', uniq(sort @tokens), '');

    return
        map { $tokens[$_], distinguish(@tokens[ $_-1, $_, $_+1 ]) }
        1 .. $#tokens-1
        ;

    }


sub distinguish {

    my ($before,
        $word,
        $after,
        ) = @_;  # contiguous sequence of three alpha-sorted words

    return substr $word, 0, 1 + max diff($word, $before), diff($word, 
+$after);

    }


sub diff {

    my ($w1,
        $w2,
        ) = @_;

    my $x = $w1 ^ $w2;

    $x =~ s{ [^\x00] .* \z }{}xms;

    return length $x;

    }

1;
[download]

File LeadingDistinct.t:

# LeadingDistinct.t       test LeadingDistinct.pm           15jun15waw

use warnings;
use strict;

use Test::More
  # tests => ?? + 1  # Test::NoWarnings adds 1 test
    'no_plan'
    ;
use Test::NoWarnings;


# normal tokens (alpha and underscore).
use constant TOKENS => qw/ab abcd abcdef  ghi ghij ghijk
    lnm lnmopq lnmopqrst  uvw xyz  dcba edcba  xyzzy xyzzz
    pqrst pqrtu
    report_time report_day reset read
    /;

use constant TOKENS_AND_UNIQUE => (
    ab          => 'ab',
    abcd        => 'abcd',
    abcdef      => 'abcde',
    dcba        => 'd',
    edcba       => 'e',
    ghi         => 'ghi',
    ghij        => 'ghij',
    ghijk       => 'ghijk',
    lnm         => 'lnm',
    lnmopq      => 'lnmopq',
    lnmopqrst   => 'lnmopqr',
    pqrst       => 'pqrs',
    pqrtu       => 'pqrt',
    read        => 'rea',
    report_day  => 'report_d',
    report_time => 'report_t',
    reset       => 'res',
    uvw         => 'u',
    xyz         => 'xyz',
    xyzzy       => 'xyzzy',
    xyzzz       => 'xyzzz',
    );

# some tokens to test handling of metacharacters.
use constant WEIRD_TOKENS => qw(foo? foo?* foo+++  foo?*+ foo???);

use constant WEIRD_TOKENS_AND_UNIQUE => (
    'foo+++' => 'foo+',
    'foo?'   => 'foo?',
    'foo?*'  => 'foo?*',
    'foo?*+' => 'foo?*+',
    'foo???' => 'foo??',
    );


BEGIN { use_ok 'LeadingDistinct'; }

is_deeply { LeadingDistinct::extract(TOKENS) }, { TOKENS_AND_UNIQUE },
    "normal chars: alphas & underscores";

is_deeply { LeadingDistinct::extract(TOKENS, WEIRD_TOKENS) },
          { TOKENS_AND_UNIQUE, WEIRD_TOKENS_AND_UNIQUE },
    "normal chars and some metacharacters";
[download]

c:\@Work\Perl\monks\gator456>perl LeadingDistinct.t
ok 1 - use LeadingDistinct;
ok 2 - normal chars: alphas & underscores
ok 3 - normal chars and some metacharacters
ok 4 - no warnings
1..4
[download]

File extract_min_uniq_2.pl:

# extract_min_uniq_2.pl                                     15jun15waw


use warnings;
use strict;

use LeadingDistinct;

use Data::Dump qw(dd);

use constant DEBUGGING => 0;
use constant {
    PR_DB1 => 1 && DEBUGGING,
    PR_DB2 => 1 && DEBUGGING,
    PR_DB3 => 1 && DEBUGGING,
    };

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

my %min_distinct = LeadingDistinct::extract(@tokens);
dd \%min_distinct if PR_DB1;

for my $k (keys %min_distinct) {
    $min_distinct{$k} = max_optional_rx($k, $min_distinct{$k});
    }
dd \%min_distinct if PR_DB2;

my ($find) =
    map qr{ (?<! [[:alpha:]_]) (?: $_) (?! [[:alpha:]_]) }xms,
    join '|',
    values %min_distinct
    ;
dd $find if PR_DB3;

while (<DATA>) {
    next unless m{ \A ($find) }xms;
    print "$1 \n";
    }


# subroutines ######################################################

sub max_optional_rx {

    my ($whole,   # full word
        $unique,  # distinctive characters at start of word
        ) = @_;

    my @tail = split //, substr $whole, length $unique;
    my $opt_tail = optional_tail(@tail);

    return qr{ \Q$unique\E $opt_tail }xms;

    }

sub optional_tail {

    my $rx = '';
    return $rx unless @_;

    $rx = quotemeta shift @_;
    for my $c (@_) {
        $c = quotemeta $c;
        $rx .= " (?: $c)?";
        }

    $rx = qr{ $rx }xms;
    return "$rx?";

    }


__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
[download]

c:\@Work\Perl\monks\gator456>perl extract_min_uniq_2.pl
report_t
report_d
res
report_time
rea
[download]