Hi,

this code parses the input linewise and prints directly to STDOUT, so you can redirect the result to another file.

while ( my $line = <DATA> ) {
    chomp $line;

    # remove the spaces from start of line
    if ( $line =~ s/^\s+// ) {
        # print line if successful replacement
        print $line;
    }
    else {
        # print newline (not for first line)
        print "\n" if $. != 1;
        print $line;
    }
}

__DATA__
first
    second
    third
first
    second
    third
first
    second
first
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Update:

shorter version:

while ( my $line = <DATA> ) {
    chomp $line;

    # remove the spaces from start of line
    if ( ! ( $line =~ s/^\s+// ) ) {
        # print newline (not for first line)
        print "\n" if $. != 1;
    }

    print $line;
}
[download]