As a partial answer to your problem, here are two subroutines which give you the previous and next values: 
use strict;

my $plus;
my $minus;
while (<DATA>) {
    chomp;
    my $next     = next_seq($_);
    my $previous = previous_seq($_);
    print "$_, $next, $previous\n";
}

sub next_seq {
    my $pattern = shift;
    chomp $pattern;
    if ($pattern =~ m/(.*?)(\d+)$/) {
        return $1 . ($2 + 1);
    }
    else {
        $pattern =~ m/(.*)(.)/;
        return $1 . chr(ord($2) + 1);
    }
}

sub previous_seq {
    my $pattern = shift;
    chomp $pattern;
    if ($pattern =~ m/(.*?)(\d+)$/) {
        return $1 . ($2 - 1);
    }
    else {
        $pattern =~ m/(.*)(.)/;
        return $1 . chr(ord($2) - 1);
    }
}

__DATA__
AAA30
BBC5
SHT12H
DAL33B
BBC49
AAA31
DAL33A
BBC6
SHT12G
BBC50
ABCZ

[download]
Warning: I'm not sure it will work with unicode-strings and anyhow it will only take into account the last character (unless the pattern ends in a one or more digits). So @ precedes A and [ follows Z.

Now all you have to do is go through the list and search for items which match the next or previous values.

CountZero

A program should be light and agile, its subroutines connected like a string of pearls. The spirit and intent of the program should be retained throughout. There should be neither too little or too much, neither needless loops nor useless variables, neither lack of structure nor overwhelming rigidity." - The Tao of Programming, 4.1 - Geoffrey James

In reply to Re: searching for strings by CountZero
in thread searching for strings by steph_bow

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.