C:\@Work\Perl>perl -wMstrict -e "print qq(\no/p: \n);  for (@ARGV) {
print qq(\"$_\" \n);
s{ ( (?: \A | [.!?]) \s*)? ([a-zA-Z]) }
   { ($1 || '') . (defined $1 ? uc $2 : lc $2) }egxms;
print qq('$_' \n\n) }"
"today is wednesday.tomorrow IS THURSDAY."
"  is tODAY wednesday? yes, but yesterDAY was tuesday! i See. "
"i thought today was...   never mind."   "what a day!"

o/p:
"today is wednesday.tomorrow IS THURSDAY."
'Today is wednesday.Tomorrow is thursday.'

"  is tODAY wednesday? yes, but yesterDAY was tuesday! i See. "
'  Is today wednesday? Yes, but yesterday was tuesday! I see. '

"i thought today was...   never mind."
'I thought today was...   Never mind.'

"what a day!"
'What a day!'
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