Answering your first question:

1. Figure out if the second character is a letter of the alphabet?

You could simply do a pattern match, like so: 
if ($str =~ m/\d[a-zA-Z]\d+/) {
  print "Ok!\n";
} else {
  print "Invalid format! Must be: [digit][letter][digit][digit] ... \n
+";
}

[download]


UPDATE: pardon for this minor slip, but you are certainly right. It should have been [a-zA-Z] instead of just \w. ;/.

_____________________ 
open(I,$0);<I>;$~=$/;$/='~';$_=<I>;($/)=/(.)$~/;s/[$~~]//g;/(v)/;$-=$-[0];s;\Q$/\E;$~;g;($/,$^)=/^(.)(.)/;
#%  xxxxxx   xx-+  xx    xxx xx  xx       xx  xx   xxx   xxxxx+ xx  xx xxxx xxxxx  ......+
#x xxxxvxxx xx  xx xv   xxxx x+ %+  ===== xx  xx  xx xx  x+  =x xx xx  xx   xx xx ...+
#x xx xx xx xx  xx xx  xx xx xxx+         xxxxxx xx   +x xx     xx+x-  xxxx xxxx ........+
#% xx xx xx xx  xx xx xx  x+ xx xx  =+=== xx  xx xxxx-xx xx  =x +x xx  xx   xx xx ...+
#% xx xx xx  -+x+  xxx+   xx xx  xx       xx  xx x+   xx xxx+xx xx  xx xxxx xx  xx ....+~
for(split/$~/){s,[ $/],,g;/(.)$/;$l=$-[0];/(.)/||next;$_=chr$-+$l;$".=($1=~/$^/)?" \u$_":$_;}print$";

In reply to Re: Comparing lower to upper case by vladb
in thread Comparing lower to upper case by bobothesmart

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