ksh has some really arcane substitution syntax. It's kinda fun but a lot of programmers don't know it, just like folks use only 20% of vi's capability.

Because folks here do not know all of that stuff, I try to use 'understandable' versions. Here is the same thing using expr, which is also portable to other shells.

Code:

lchr=`expr substr $a ${#a} 1`

the substr operand for expr takes:

$a - string to work on

${#a} - a starting point in the string - in this case the
last character ${#a} is the length of a string.

1 - number of characters after the starting point to return

Generally, if you need a lot of string and array features, try bash.
ksh has most of them but some of it is completely counterintuitive. IMO.