how to change date-format in a log file using bash, avoiding while loop

Question

This is not a new question here and here, but the details make it differ.

My input log file looks like:

TEMP MON -=- Sat Aug 15 02:20:24 EEST 2020 -=-          


        

Answer 1

Using core module Time::Piece in Perl:

perl -MTime::Piece -pe 's/-=-\s+\K(.*)(?=\s+-=-)/convert($1)/e;
  sub convert {
    $s = $_[0];
    $s =~ s/\s+EEST\s+/ /;
    $t = Time::Piece->strptime($s, "%a %b %d %T %Y");
    $res = $t->strftime("%Y-%m-%d_%H:%M:%S");
    "$res EEST"
 }' file