Please see

Script: 

#! /usr/local/bin/perl -w

use strict;

my $final_string = '';

while (<>) {
    chomp;

    if (m/([mM]{0,1})
          ([dD]{0,1})
          ([cC]{0,1})
          ([lL]{0,1})
          ([xX]{0,1})
          ([vV]{0,1})
          ([iI]{0,1})\b/x) {

    if (length($1) == 0) {
        $final_string = "\.";
    } else {
        $final_string = $1;
    }
    if (length($2) == 0) {
        $final_string .= "\.";
    } else {
        $final_string .= $2;
    }
    if (length($3) == 0) {
        $final_string .= "\.";
    } else {
        $final_string .= $3;
    }
    if (length($4) == 0) {
        $final_string .= "\.";
    } else {
        $final_string .= $4;
    }
    if (length($5) == 0) {
        $final_string .= "\.";
    } else {
        $final_string .= $5;
    }
    if (length($6) == 0) {
        $final_string .= "\.";
    } else {
        $final_string .= $6;
    }
    if (length($7) == 0) {
        $final_string .= "\.";
    } else {
        $final_string .= $7;
    }

        print "$final_string\n";
        $final_string = '';

    } 
}

[download]

Input: 

I
IV
V
VI
IX
X
XI
XIV
XV
XVI
XIX
X
XL
LX
XC
CLXIX
CDXLVI
MCMXCVI
MDCLI

[download]

Actual Output: 

......I
.......
.....V.
.....VI
.......
....X..
....X.I
.......
....XV.
....XVI
.......
....X..
.......
...LX..
.......
.......
.......
.......
MDCL..I

[download]

Desired Output: 

......I
.....V.
.....V.
.....VI
....X..
....X..
....X.I
....XV.
....XV.
....XVI
....X.I
....X..
....X..
...LX..
....X..
..CLX.I
.D..XVI
M.C.XVI
MDCL..I

[download]

The regex and the sample data have been somewhat contrived to fit Roman Numerals. The real regex/data is similar, but character classes may contain a variable number of characters. Certain classes later in the regex may contain some or all characters contained in prior classes.

Characters must match both the class AND the position. I want to ignore characters that are "out of order" (the "I" in "IV") but allow subsequent matches of characters that are in order (the "V" in "IV"). I want to make sure a period (".") replaces any character that doesn't match both the character and its designated position.

I am not sure how to change my regex to accomplish my goals. Any help would be appreciated.

for a complete description of my quandry, including my code, sample input, actual output, and an example of desired output.

I need help modifying my regex to get my desired output, but am not sure how to fix it.

Your wisdom is greatly appreciated.


Updated to use < r e a d m o r e > tags rather than my scratchpad, on the excellent advice of reasonablekeith.

In reply to Help with a Regex by planetscape

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