#! perl -slw
use strict;

# Set up some test data.
my $text = 'The quick brown fox jumps over the lazy dog';
my @tests = map{
    my $t = $text;
    substr($t, rand( length $text ), 0 ) = $_;
    $t;
} map{
    substr 'vacation.msg', $_
} 0 ..6;

print "Before\n";
print for @tests;

#
s[v?a?c?a?t?i?o?n\.msg][] for @tests;

print "\nAfter\n";
print for @tests;

__END__
P:\>junk
Before

The quick vacation.msgbrown fox jumps over the lazy dog
The quick brown fox jumps over the laacation.msgzy dog
The quick bcation.msgrown fox jumps over the lazy dog
Theation.msg quick brown fox jumps over the lazy dog
The quick brown fotion.msgx jumps over the lazy dog
The quick brown fox jumps ovion.msger the lazy dog
Thon.msge quick brown fox jumps over the lazy dog

After

The quick brown fox jumps over the lazy dog
The quick brown fox jumps over the lazy dog
The quick brown fox jumps over the lazy dog
The quick brown fox jumps over the lazy dog
The quick brown fox jumps over the lazy dog
The quick brown fox jumps oer the lazy dog
The quick brown fox jumps over the lazy dog
[download]

Note: If the character(s) of the 'other text' immediately preceding the partial insertion match the omitted part of the insertion, then they are indistinguishable from the case where the insertion was longer and are also removed as in the second from last test shown above.