have to validate each line of file A to check if it exceeds 70 characters, if yes then truncate from 70th character and put it in next line.
i.e. each line a file should not exceed 70 characters

You mean check if it has or exceeds 70 characters?
i.e. each line should not exceed 69 characters

my $smallchunk = substr($line,0,$maxlen-1);

Your $smallchunk will be 69 characters or less.

perl -lne 'chomp; print join "\n", unpack("(a69)*", $_)' textfile > tm
+pfile
[download]

FYI: Text::Wrap is a paragraph formatter, and may not break your lines at exactly after the 69th character, given $Text::Wrap::columns = 70.

Update: Applied change - thanks, jwkrahn!

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