in reply to replace multiple newline characters

Provided your input-file is small enough to be read into memory, you can do this with a one-liner: 
perl -i.old -0777 -pe 's/\n+/\n/sg' input.txt

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the original version of the file is kept as input.txt.old.

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Re^2: replace multiple newline characters
by hippo (Archbishop) on May 15, 2018 at 08:15 UTC
    Provided your input-file is small enough to be read into memory

    Here's one without that constraint:

    perl -i.old -ne 'print if /./;' input.txt
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[d/l]

      Even shorter :-) (Update: Sorry, not quite the same, see replies.)

      $ perl -lp000e1  input.txt >output.txt

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      $ perl -MO=Deparse -lp000e1

BEGIN { $/ = ""; $\ = "\n"; }
LINE: while (defined($_ = readline ARGV)) {
    chomp $_;
    '???';
}
continue {
    die "-p destination: $!\n" unless print $_;
}

      [download]

      Or edited:

      use warnings;
use strict;

local ($/,$\) = ("","\n");
while (<>) {
    chomp;
    print;
}

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[d/l]
[select]

        Shorter, yes, but it looks like you've re-introduced the "input-file is small enough to be read into memory" constraint. Or have I missed something?

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