10-05-2018
Quote:
Originally Posted by
Don Cragun
It might, or might not, be faster depending on what hardware you're using, what operating system you're using, what version of perl you're using, and what other tools you're using as a comparison. But, note that even though this is only printing the first and last lines of the compressed file, it can't avoid reading the entire compressed file and uncompressing all of the compressed data to be able to determine the contents of the last line in the file. (Decompression can't start at random places in the file; it must start at the beginning and progress byte by byte from there.)
I know all that, but there may be a significant gain because we only create the process once instead of creating 4 * n file.
Where I have a doubt is that perl does not emulate seek by just passing through a memory buffer.
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LEARN ABOUT ULTRIX
uncompact
compact(1) General Commands Manual compact(1)
Name
compact, uncompact, ccat - compress and uncompress files, and cat them
Syntax
compact [name...]
uncompact [name...]
ccat [file...]
Description
The command compresses the named files using an adaptive Huffman code. If no file names are given, the standard input is compacted to the
standard output. The command operates as an on-line algorithm. Each time a byte is read, it is encoded immediately according to the cur-
rent prefix code. This code is an optimal Huffman code for the set of frequencies seen so far. It is unnecessary to prepend a decoding
tree to the compressed file since the encoder and the decoder start in the same state and stay synchronized. Furthermore, and can operate
as filters. In particular,
... | compact | uncompact | ...
operates as a (very slow) no-op.
When an argument file is given, it is compacted and the resulting file is placed in file.C; file is unlinked. The first two bytes of the
compacted file code the fact that the file is compacted. This code is used to prohibit recompaction.
The amount of compression to be expected depends on the type of file being compressed. Typical values of compression are: Text (38%), Pas-
cal Source (43%), C Source (36%) and Binary (19%). These values are the percentages of file bytes reduced.
The command restores the original file from a file compressed by If no file names are given, the standard input is uncompacted to the stan-
dard output.
The command cats the original file from a file compressed by without uncompressing the file.
The command is present only for compatibility. In general, the command runs faster and gives better compression.
Restrictions
The last segment of the file name must contain fewer than thirteen characters to allow space for the appended '.C'.
Files
compacted file created by compact, removed by uncompact
See Also
compress(1)
compact(1)