I tried the code and it did not work. After a little experimenting following code did work. I added the orignal one liner to the generator to validate it. The mistakes that I saw were two fold. First base should have be 26 not 25. Second the magical text increment behavior is not equivalent to incrementing numbers.

9 goes to 10
z goes to aa  not a0 

as a result the equivs have to run a-z === 1-26 not 0-25 and the answer offset is 2 not 1.

#!/usr/bin/perl -w

# Convert pseudo-base26 number (digits: a-z) to decimal
# really intended to find the ending number needed in
# the for loop for any given string to be used

my $num = 1;        #  was  $num = 1
my $char = "a";
my $answer = 0;

until ($char eq "aa") {
    $equiv{$char}=$num;
    $num++; $char++;
}

print "Enter your lowercase string: ";
chomp($string = <STDIN>);
@strArray=reverse(split(//,$string));

for ($i = 0; $i < @strArray; $i++) {
    $answer += ($equiv{$strArray[($i)]} * (26 ** $i)); 
                                     # was 25 ** $i   
}
$offset = $answer - 2;
print $offset,"\n";

my $A="a";for(0..$offset){$A++;}print"$A";
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