diff options
Diffstat (limited to 'man1p/compress.1p')
| -rw-r--r-- | man1p/compress.1p | 216 |
1 files changed, 216 insertions, 0 deletions
diff --git a/man1p/compress.1p b/man1p/compress.1p new file mode 100644 index 000000000..ed7f5d231 --- /dev/null +++ b/man1p/compress.1p @@ -0,0 +1,216 @@ +.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved +.TH "COMPRESS" P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual" +.\" compress +.SH NAME +compress \- compress data +.SH SYNOPSIS +.LP +\fBcompress\fP \fB[\fP\fB-fv\fP\fB][\fP\fB-b\fP \fIbits\fP\fB][\fP\fIfile\fP +\fB\&...\fP\fB]\fP\fB +.br +.sp +compress\fP \fB[\fP\fB-cfv\fP\fB][\fP\fB-b\fP \fIbits\fP\fB][\fP\fIfile\fP\fB]\fP\fB\fP +\fB +.br +\fP +.SH DESCRIPTION +.LP +The \fIcompress\fP utility shall attempt to reduce the size of the +named files by using adaptive Lempel-Ziv coding algorithm. +.TP 7 +\fBNote:\fP +Lempel-Ziv is US Patent 4464650, issued to William Eastman, Abraham +Lempel, Jacob Ziv, Martin Cohn on August 7th, 1984, and +assigned to Sperry Corporation. +.LP +Lempel-Ziv-Welch compression is covered by US Patent 4558302, issued +to Terry A. Welch on December 10th, 1985, and assigned to +Sperry Corporation. +.sp +On systems not supporting adaptive Lempel-Ziv coding algorithm, the +input files shall not be changed and an +error value greater than two shall be returned. Except when the output +is to the standard output, each file shall be replaced by +one with the extension \fB.Z\fP. If the invoking process has appropriate +privileges, the ownership, modes, access time, and +modification time of the original file are preserved. If appending +the \fB.Z\fP to the filename would make the name exceed +{NAME_MAX} bytes, the command shall fail. If no files are specified, +the standard input shall be compressed to the standard +output. +.SH OPTIONS +.LP +The \fIcompress\fP utility shall conform to the Base Definitions volume +of IEEE\ Std\ 1003.1-2001, Section 12.2, Utility Syntax Guidelines. +.LP +The following options shall be supported: +.TP 7 +\fB-b\ \fP \fIbits\fP +Specify the maximum number of bits to use in a code. For a conforming +application, the \fIbits\fP argument shall be: +.sp +.RS +.nf + +\fB9 <=\fP \fIbits\fP \fB<= 14 +\fP +.fi +.RE +.LP +The implementation may allow \fIbits\fP values of greater than 14. +The default is 14, 15, or 16. +.TP 7 +\fB-c\fP +Cause \fIcompress\fP to write to the standard output; the input file +is not changed, and no \fB.Z\fP files are created. +.TP 7 +\fB-f\fP +Force compression of \fIfile\fP, even if it does not actually reduce +the size of the file, or if the corresponding \fIfile\fP +\fB\&.Z\fP file already exists. If the \fB-f\fP option is not given, +and the process is not running in the background, the user is +prompted as to whether an existing \fIfile\fP \fB.Z\fP file should +be overwritten. +.TP 7 +\fB-v\fP +Write the percentage reduction of each file to standard error. +.sp +.SH OPERANDS +.LP +The following operand shall be supported: +.TP 7 +\fIfile\fP +A pathname of a file to be compressed. +.sp +.SH STDIN +.LP +The standard input shall be used only if no \fIfile\fP operands are +specified, or if a \fIfile\fP operand is \fB'-'\fP +\&. +.SH INPUT FILES +.LP +If \fIfile\fP operands are specified, the input files contain the +data to be compressed. +.SH ENVIRONMENT VARIABLES +.LP +The following environment variables shall affect the execution of +\fIcompress\fP: +.TP 7 +\fILANG\fP +Provide a default value for the internationalization variables that +are unset or null. (See the Base Definitions volume of +IEEE\ Std\ 1003.1-2001, Section 8.2, Internationalization Variables +for +the precedence of internationalization variables used to determine +the values of locale categories.) +.TP 7 +\fILC_ALL\fP +If set to a non-empty string value, override the values of all the +other internationalization variables. +.TP 7 +\fILC_CTYPE\fP +Determine the locale for the interpretation of sequences of bytes +of text data as characters (for example, single-byte as +opposed to multi-byte characters in arguments). +.TP 7 +\fILC_MESSAGES\fP +Determine the locale that should be used to affect the format and +contents of diagnostic messages written to standard +error. +.TP 7 +\fINLSPATH\fP +Determine the location of message catalogs for the processing of \fILC_MESSAGES +\&.\fP +.sp +.SH ASYNCHRONOUS EVENTS +.LP +Default. +.SH STDOUT +.LP +If no \fIfile\fP operands are specified, or if a \fIfile\fP operand +is \fB'-'\fP , or if the \fB-c\fP option is specified, +the standard output contains the compressed output. +.SH STDERR +.LP +The standard error shall be used only for diagnostic and prompt messages +and the output from \fB-v\fP. +.SH OUTPUT FILES +.LP +The output files shall contain the compressed output. The format of +compressed files is unspecified and interchange of such +files between implementations (including access via unspecified file +sharing mechanisms) is not required by +IEEE\ Std\ 1003.1-2001. +.SH EXTENDED DESCRIPTION +.LP +None. +.SH EXIT STATUS +.LP +The following exit values shall be returned: +.TP 7 +\ 0 +Successful completion. +.TP 7 +\ 1 +An error occurred. +.TP 7 +\ 2 +One or more files were not compressed because they would have increased +in size (and the \fB-f\fP option was not +specified). +.TP 7 +>2 +An error occurred. +.sp +.SH CONSEQUENCES OF ERRORS +.LP +The input file shall remain unmodified. +.LP +\fIThe following sections are informative.\fP +.SH APPLICATION USAGE +.LP +The amount of compression obtained depends on the size of the input, +the number of \fIbits\fP per code, and the distribution of +common substrings. Typically, text such as source code or English +is reduced by 50-60%. Compression is generally much better than +that achieved by Huffman coding or adaptive Huffman coding ( \fIcompact\fP), +and takes less time to compute. +.LP +Although \fIcompress\fP strictly follows the default actions upon +receipt of a signal or when an error occurs, some unexpected +results may occur. In some implementations it is likely that a partially +compressed file is left in place, alongside its +uncompressed input file. Since the general operation of \fIcompress\fP +is to delete the uncompressed file only after the \fB.Z\fP +file has been successfully filled, an application should always carefully +check the exit status of \fIcompress\fP before +arbitrarily deleting files that have like-named neighbors with \fB.Z\fP +suffixes. +.LP +The limit of 14 on the \fIbits\fP option-argument is to achieve portability +to all systems (within the restrictions imposed by +the lack of an explicit published file format). Some implementations +based on 16-bit architectures cannot support 15 or 16-bit +uncompression. +.SH EXAMPLES +.LP +None. +.SH RATIONALE +.LP +None. +.SH FUTURE DIRECTIONS +.LP +None. +.SH SEE ALSO +.LP +\fIuncompress\fP , \fIzcat\fP +.SH COPYRIGHT +Portions of this text are reprinted and reproduced in electronic form +from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology +-- Portable Operating System Interface (POSIX), The Open Group Base +Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of +Electrical and Electronics Engineers, Inc and The Open Group. In the +event of any discrepancy between this version and the original IEEE and +The Open Group Standard, the original IEEE and The Open Group Standard +is the referee document. The original Standard can be obtained online at +http://www.opengroup.org/unix/online.html . |