Reverse the order of lines in a text file while preserving the contents of each line: Difference between revisions
Reverse the order of lines in a text file while preserving the contents of each line (view source)
Revision as of 01:32, 4 August 2021
, 2 years ago→{{header|Raku}}: Add a no / few assumptions version
(Added XPL0 example.) |
Thundergnat (talk | contribs) (→{{header|Raku}}: Add a no / few assumptions version) |
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=={{header|Raku}}==
Not going to bother testing with the task recommended file. It demonstrated nothing to do with file handling, record separators, memory conservation or anything useful. May as well just be "Reverse this list" for all the good it does.
==Lots of assumptions==
Simplest thing that could possibly satisfy the extremely vague task description and completely glossing over all of the questions raised on the discussion page.
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<lang perl6>.put for reverse lines</lang>
==Few assumptions==
Processes a small (configurable) number of bytes at a time so file can be multi-terabyte and it will handle with ease. ''Does'' assume Latin 1 for reduced complexity.
Run the following to generate nul.txt. (digits 1 through 6 repeated 8 times with double null as record separators):
raku -e'print join "\x00\x00", (1..6).map: * x 8' > nul.txt
<lang perl6>my $input-record-separator = "\x00\x00";
my $fh = open("nul.txt".IO, :r, :bin);
$fh.seek(0, SeekFromEnd); # start at the end of the file
my $bytes = 5 min $fh.tell - 1; # read in file 5 bytes at a time (or whatever)
$fh.seek(-$bytes, SeekFromCurrent);
my $buffer = $fh.read($bytes).decode('Latin1'); # assume Latin1 for reduced complexity
loop {
my $seek = ($fh.tell < $bytes * 2) ?? -$fh.tell !! -$bytes * 2;
$fh.seek($seek, SeekFromCurrent);
$buffer = $buffer R~ $fh.read((-$seek - $bytes) max 0).decode('Latin1');
if $buffer.contains: $input-record-separator {
my @rest;
($buffer, @rest) = $buffer.split: $input-record-separator;
.say for reverse @rest; # emit any full records that have been processed
}
last if $fh.tell < $bytes;
}
say $buffer; # emit any remaining record</lang>
{{out}}
<pre>66666666
55555555
44444444
33333333
22222222
11111111</pre>
=={{header|REXX}}==
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