It is also possible to take advantage of the @LAST_MATCH_START (in English,  @- in Perlish) array (see perlvar) associated with the capture group variables $1, $2, etc. 
>perl -wMstrict -le
"$ARGV[$#ARGV] =~ m{ (\S) \s* \z }xms;
 my ($lastchr, $lastpos) =
   defined $1 ? ($1, $-[1]) : ('absent', -1);
 print '----- output -----';
 print qq{last non-ws char is '$lastchr' at index $lastpos};
"
"Message Line 1" "Message Line 2" "Message Line 3"
"Prompt:             "
----- output -----
last non-ws char is ':' at index 6

[download]
Update: Changed link to use English version of  @- to avoid rendering problems.

In reply to Re: A Better Way to Find the Position of the Last Non-Whitespace Character in the Last Element of an Array. by AnomalousMonk
in thread A Better Way to Find the Position of the Last Non-Whitespace Character in the Last Element of an Array. by NateTut

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