FREEZE
Section: User Commands (1)
Updated: local
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NAME
freeze, unfreeze, melt, fcat - compress and uncompress files
SYNOPSIS
freeze
[
-cdfvVgx
] [
filename | type ...
]
unfreeze
[
-cfvV
] [
filename ...
]
melt
[
-cfvV
] [
filename ...
]
fcat
[
filename ...
]
DESCRIPTION
Compresses the specified files or standard input.
Each file is replaced by a file with the extension
.F,
but only if the file got smaller. If no files are specified,
the compression is applied to the standard input
and is written to standard output regardless of the results.
Compressed files can be restored to their original form by specifying the
-d
option, or by running
melt
or
unfreeze
(both linked to
freeze),
on the
.F
files or the standard input.
If the output file exists, it will not be overwritten unless the
-f
flag is given. If
-f
is not specified and
freeze
is run in the foreground,
the user is prompted
as to whether the file should be overwritten.
If the
-g
flag is given, a slightly less powerful (compression
rate is 1.5% less), but somewhat faster heuristic is used. This flag can be
used more than once (this mode is quite useful when freezing bitmaps) for
additional speedup.
If you want to improve compression rate at the cost of speed, use
-x
flag. It means "maximum compression" (the speed may degrade
substantially when freezing bitmaps).
If the
-f
flag is given, all files specified are replaced with
.F
files - even if the file didn't get smaller.
When file names are given, the ownership (if run by root), modes, accessed
and modified times are maintained between the file and its
.F
version. In this respect,
freeze
can be used for archival purposes, yet can still be used with
make(1)
after melting.
The
-c
option causes the results of the freeze/melt operation to be written
to stdout; no files are changed. The
fcat
program is the same as specifying
-c
to
melt
(all files are unpacked and written to stdout).
The
-v
(verbose) option causes the diagnostics (at the end of each file processing)
to be printed to stderr, and the
-vv
option causes the progress indicator to be drawn to the same place.
Type
is a token preceded by a '+' or a '--', which defines the type
of following files in the command string. An explicite definition
of the file's type can give up to 2% of additional compression.
The list of types is stored in file
/usr/local/lib/freeze.cnf.
Types may be abbreviated while not ambigious. You can also determine
values for the static Huffman table by using a list of 8 numbers
separated by commas instead of
type.
Freeze
uses the Lempel-Ziv algorithm on the first pass and the dynamic
Huffman algorithm on the second one. The size of sliding window
is 8K, and the maximum length of matched string is 256.
The positions on the window are coded using a static Huffman table.
A two byte magic number is prepended to the file
to ensure that neither melting of random text nor refreezing of
already frozen text are attempted. In addition, the characteristics
of the static Huffman table being used during
freeze
is written to the file so that these characteristics may be adapted
to concrete conditions.
The amount of compression obtained depends on the size of the
input file and the distribution of character substrings and their
probabilities.
Typically, text files, such as C programs,
are reduced by 60-75%, executable files are reduced by 50%.
Compression is generally much better than that achieved by
LZW coding (as used in
compress),
or Huffman coding
(pack),
though takes more time to compute.
If the
-V
(version) flag is given, the program's version number and compilation
options are printed.
The exit status is normally 0;
if the last file gets bigger after freezing, the exit status is 2;
if an error occurs, the exit status is 1.
SEE ALSO
compact(1),
pack(1),
compress(1)
DIAGNOSTICS
Unknown flag:
'x';
Usage: freeze [-cdfvVg] [file|+type ...]
Invalid options were specified on the command line.
file:
not in frozen format
The specified file has not been frozen.
file:
already has .F suffix -- no change
Cannot compress a file that has a ".F" suffix.
mv(1)
the file to a different name and try again.
file:
filename too long to tack on .F
The specified file cannot be compressed because its filename is longer than
12 characters.
mv(1)
the file to a different name and try again. This message does not occur on
4.XBSD systems.
file
already exists; do you wish to overwrite (y or n)?
Respond "y" if you want the output file to be replaced; "n" if you want it
to be left alone.
file:
xx%
or
xxxK
These message fragments are written during the processing of a file, if
-vv
option was given in the command line (in percents, if the length of file
being processed is known; in Kbytes otherwise).
Freezing:
xx.xx% (y.yy
bits)
This message fragment gives the percentage of the input file that has been
saved by freezing and the number of remaining bits per byte of original file.
-- not a regular file: unchanged
This message fragment is written when the input file is not a regular file.
The input file is left unchanged.
-- has
xx
other links: unchanged
This message fragment is written when the input file has links. The input
file is left unchanged. See
ln(1)
for more information.
-- file unchanged
This message fragment is written when no savings are achieved by
freezing. The input file is left unchanged.
-- replaced with
file
This message fragment is written when a file has been sucessfully
frozen/melt.
Using "
type
" type
This message indicates a successful switching to
position table for mentioned file type.
"
xxx
" - no such file type
or
xxx
- a list of 8 numbers expected
This message means the given file type does not exist or
the given string contains a comma, but is not a valid list
of values for static Huffman table.
melt: corrupt input
This message fragment is written when an error in header or
unexpected end of frozen file is detected. Partial
(or empty, is there was an error in the header) file is created.
already frozen -- file unchanged
This message fragment is written when an input file already has
Freeze's magic header.
Invalid position table
or
"
type
" - invalid entry
These messages appear only if Freeze has been made with incorrect
data for static Huffman table. It does never appear when freeze
is called from a public access directory.
Unknown header format
Unknown values of flag bits were discovered in the header
of frozen file.
BUGS
Found bugs descriptions, incompatibilities, etc. please send to
leo@ipmce.su.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- SEE ALSO
-
- DIAGNOSTICS
-
- BUGS
-
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