Assuming you are working on something like a cryptogram problem, something like this:

#!/usr/bin/perl

use strict; # https://perlmonks.org/?node_id=11146148
use warnings;

my $template = 'abcdefa';

my $regex = '';
my %used;
for my $char ( split //, $template )
  {
  if( exists $used{$char} ) # seen before
    {
    $regex .= "\\$used{$char}";
    }
  else # new different character
    {
    $regex .= join '', map("(?!\\$_)", values %used), "(.)";
    $used{$char} = 1 + keys %used;
    }
  }

my $qr = qr/^$regex$/; # the real regex

use Data::Dump 'dd'; dd $qr;

@ARGV = '/usr/share/dict/words';
/$qr/ and print, exit while <>; # show first match
[download]

Outputs:

qr/^(.)(?!\1)(.)(?!\2)(?!\1)(.)(?!\2)(?!\1)(?!\3)(.)(?!\4)(?!\3)(?!\2)
+(?!\1)(.)(?!\5)(?!\2)(?!\1)(?!\3)(?!\4)(.)\1$/
algebra
[download]

EDIT: a couple of newlines makes the regex easier to read (still same algorithm)

#!/usr/bin/perl

use strict; # https://perlmonks.org/?node_id=11146148
use warnings;

my $template = 'abcdefa';

my $regex = '';
my %used;
for my $char ( split //, $template )
  {
  if( exists $used{$char} ) # seen before
    {
    $regex .= "\\$used{$char}\n";
    }
  else # new different character
    {
    $regex .= join '', map("(?!\\$_)", sort values %used), "(.)\n";
    $used{$char} = 1 + keys %used;
    }
  }

my $qr = qr/^$regex$/x; # the real regex

use Data::Dump 'dd'; dd $qr;

@ARGV = '/usr/share/dict/words';
use List::AllUtils qw{ sample };
print sample 10, grep /$qr/, <>
[download]

Outputs:

qr/^(.)
(?!\1)(.)
(?!\1)(?!\2)(.)
(?!\1)(?!\2)(?!\3)(.)
(?!\1)(?!\2)(?!\3)(?!\4)(.)
(?!\1)(?!\2)(?!\3)(?!\4)(?!\5)(.)
\1
$/x
swipe's
enforce
tugboat
discard
slogans
sailors
neutron
shock's
singles
snipe's
[download]

---

---

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! —

• How do I compose an effective node title?
• How do I post a question effectively?
• Markup in the Monastery

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:
	&		&
	<		&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.