| compress.1 (c3aac50f284c6cca5b4f2eb46aaa13812cb8b630) | compress.1 (fae643c5795db2d9bf031c6db8a70ba8d6978c62) |
|---|---|
| 1.\" Copyright (c) 1986, 1990, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" This code is derived from software contributed to Berkeley by 5.\" James A. Woods, derived from original work by Spencer Thomas 6.\" and Joseph Orost. 7.\" 8.\" Redistribution and use in source and binary forms, with or without --- 77 unchanged lines hidden (view full) --- 86.Pp 87If no files are specified, the standard input is compressed or uncompressed 88to the standard output. 89If either the input and output files are not regular files, the checks for 90reduction in size and file overwriting are not performed, the input file is 91not removed, and the attributes of the input file are not retained. 92.Pp 93The options are as follows: | 1.\" Copyright (c) 1986, 1990, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" This code is derived from software contributed to Berkeley by 5.\" James A. Woods, derived from original work by Spencer Thomas 6.\" and Joseph Orost. 7.\" 8.\" Redistribution and use in source and binary forms, with or without --- 77 unchanged lines hidden (view full) --- 86.Pp 87If no files are specified, the standard input is compressed or uncompressed 88to the standard output. 89If either the input and output files are not regular files, the checks for 90reduction in size and file overwriting are not performed, the input file is 91not removed, and the attributes of the input file are not retained. 92.Pp 93The options are as follows: |
| 94.Bl -tag -width Ds | 94.Bl -tag -width indent |
| 95.It Fl b 96Specify the 97.Ar bits 98code limit (see below). 99.It Fl c 100Compressed or uncompressed output is written to the standard output. 101No files are modified. 102.It Fl f --- 14 unchanged lines hidden (view full) --- 117.Fl b 118flag is reached (the default is 16). 119.Ar Bits 120must be between 9 and 16. 121.Pp 122After the 123.Ar bits 124limit is reached, | 95.It Fl b 96Specify the 97.Ar bits 98code limit (see below). 99.It Fl c 100Compressed or uncompressed output is written to the standard output. 101No files are modified. 102.It Fl f --- 14 unchanged lines hidden (view full) --- 117.Fl b 118flag is reached (the default is 16). 119.Ar Bits 120must be between 9 and 16. 121.Pp 122After the 123.Ar bits 124limit is reached, |
| 125.Nm compress | 125.Nm |
| 126periodically checks the compression ratio. 127If it is increasing, | 126periodically checks the compression ratio. 127If it is increasing, |
| 128.Nm compress | 128.Nm |
| 129continues to use the existing code dictionary. 130However, if the compression ratio decreases, | 129continues to use the existing code dictionary. 130However, if the compression ratio decreases, |
| 131.Nm compress | 131.Nm |
| 132discards the table of substrings and rebuilds it from scratch. This allows 133the algorithm to adapt to the next "block" of the file. 134.Pp 135The 136.Fl b 137flag is omitted for 138.Nm uncompress 139since the --- 8 unchanged lines hidden (view full) --- 148input, the number of 149.Ar bits 150per code, and the distribution of common substrings. 151Typically, text such as source code or English is reduced by 50\-60%. 152Compression is generally much better than that achieved by Huffman 153coding (as used in the historical command pack), or adaptive Huffman 154coding (as used in the historical command compact), and takes less 155time to compute. | 132discards the table of substrings and rebuilds it from scratch. This allows 133the algorithm to adapt to the next "block" of the file. 134.Pp 135The 136.Fl b 137flag is omitted for 138.Nm uncompress 139since the --- 8 unchanged lines hidden (view full) --- 148input, the number of 149.Ar bits 150per code, and the distribution of common substrings. 151Typically, text such as source code or English is reduced by 50\-60%. 152Compression is generally much better than that achieved by Huffman 153coding (as used in the historical command pack), or adaptive Huffman 154coding (as used in the historical command compact), and takes less 155time to compute. |
| 156.Pp | 156.Sh DIAGNOSTICS |
| 157The | 157The |
| 158.Nm compress | 158.Nm |
| 159utility exits 0 on success, and >0 if an error occurs. 160.Sh SEE ALSO 161.Rs 162.%A Welch, Terry A. 163.%D June, 1984 164.%T "A Technique for High Performance Data Compression" 165.%J "IEEE Computer" 166.%V 17:6 167.%P pp. 8-19 168.Re 169.Sh HISTORY 170The 171.Nm 172command appeared in 173.Bx 4.3 . | 159utility exits 0 on success, and >0 if an error occurs. 160.Sh SEE ALSO 161.Rs 162.%A Welch, Terry A. 163.%D June, 1984 164.%T "A Technique for High Performance Data Compression" 165.%J "IEEE Computer" 166.%V 17:6 167.%P pp. 8-19 168.Re 169.Sh HISTORY 170The 171.Nm 172command appeared in 173.Bx 4.3 . |