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All Rights Reserved 46 .\" 47 .TH COMPRESS 1 "Feb 5, 2020" 48 .SH NAME 49 compress, uncompress, zcat \- compress, uncompress files or display expanded 50 files 51 .SH SYNOPSIS 52 .nf 53 \fBcompress\fR [\fB-fv/\fR] [\fB-b\fR \fIbits\fR] [\fIfile\fR]... 54 .fi 55 56 .LP 57 .nf 58 \fBcompress\fR \fB-c\fR [\fB-fv\fR] [\fB-b\fR \fIbits\fR] [\fIfile\fR] 59 .fi 60 61 .LP 62 .nf 63 \fBuncompress\fR [\fB-fv\fR] [\fB-c | -/\fR] [\fIfile\fR]... 64 .fi 65 66 .LP 67 .nf 68 \fBzcat\fR [\fIfile\fR]... 69 .fi 70 71 .SH DESCRIPTION 72 .SS "compress" 73 The \fBcompress\fR utility attempts to reduce the size of the named files by 74 using adaptive Lempel-Ziv coding. Except when the output is to the standard 75 output, each file is replaced by one with the extension \fB\&.Z\fR, while 76 keeping the same ownership modes, change times and modification times, ACLs, 77 and extended attributes. The compress utility also attempts to set the owner and 78 group of \fIfile\fR\fB\&.Z\fR to the owner and group of file, but does not fail 79 if this cannot be done. If appending the \fB\&.Z\fR to the file pathname would 80 make the pathname exceed \fB1023\fR bytes, the command fails. If no files are 81 specified, the standard input is compressed to the standard output. 82 .sp 83 .LP 84 The amount of compression obtained depends on the size of the input, the number 85 of \fIbits\fR per code, and the distribution of common substrings. Typically, 86 text such as source code or English is reduced by 50\(mi60%. Compression is 87 generally much better than that achieved by Huffman coding (as used in 88 \fBpack\fR(1)) and it takes less time to compute. The \fIbits\fR parameter 89 specified during compression is encoded within the compressed file, along with 90 a magic number to ensure that neither decompression of random data nor 91 recompression of compressed data is subsequently allowed. 92 .SS "uncompress" 93 The \fBuncompress\fR utility restores files to their original state after they 94 have been compressed using the \fBcompress\fR utility. If no files are 95 specified, the standard input is uncompressed to the standard output. 96 .sp 97 .LP 98 This utility supports the uncompressing of any files produced by 99 \fBcompress\fR. For files produced by \fBcompress\fR on other systems, 100 \fBuncompress\fR supports 9- to 16-bit compression (see \fB-b\fR). 101 .SS "zcat" 102 The \fBzcat\fR utility writes to standard output the uncompressed form of files 103 that have been compressed using \fBcompress\fR. It is the equivalent of 104 \fBuncompress\fR \fB-c\fR. Input files are not affected. 105 .SH OPTIONS 106 The following options are supported: 107 .sp 108 .ne 2 109 .na 110 \fB\fB-b\fR \fIbits\fR\fR 111 .ad 112 .RS 11n 113 Sets the upper limit (in bits) for common substring codes. \fIbits\fR must be 114 between 9 and 16 (16 is the default). Lowering the number of bits result in 115 larger, less compressed files. 116 .RE 117 118 .sp 119 .ne 2 120 .na 121 \fB\fB-c\fR\fR 122 .ad 123 .RS 11n 124 Writes to the standard output; no files are changed and no \fB\&.Z\fR files are 125 created. The behavior of \fBzcat\fR is identical to that of `\fBuncompress\fR 126 \fB-c\fR'. 127 .RE 128 129 .sp 130 .ne 2 131 .na 132 \fB\fB-f\fR\fR 133 .ad 134 .RS 11n 135 When compressing, forces compression of \fIfile\fR, even if it does not 136 actually reduce the size of the file, or if the corresponding 137 \fIfile\fR\fB\&.Z\fR file already exists. 138 .sp 139 If the \fB-f\fR option is not specified, and the process is not running in the 140 background, prompts to verify whether an existing file should be overwritten. 141 If the response is affirmative, the existing file is overwritten. When 142 uncompressing, does not prompt for overwriting files. If the \fB-f\fR option is 143 not specified, and the process is not running in the background, prompts to 144 verify whether an existing file should be overwritten. If the standard input is 145 not a terminal and \fB-f\fR is not specified, writes a diagnostic message to 146 standard error and exits with a status greater than \fB0\fR. 147 .RE 148 149 .sp 150 .ne 2 151 .na 152 \fB\fB-v\fR\fR 153 .ad 154 .RS 11n 155 Verbose. Writes to standard error messages concerning the percentage reduction 156 or expansion of each file. 157 .RE 158 159 .sp 160 .ne 2 161 .na 162 \fB\fB-/\fR\fR 163 .ad 164 .RS 11n 165 When compressing or decompressing, copies any extended system attributes 166 associated with the source file to the target file and copies any extended 167 system attributes associated with extended attributes of the source file to the 168 corresponding extended attributes associated with the target file. If any 169 extended system attributes cannot be copied, the original file is retained, a 170 diagnostic is written to \fBstderr\fR, and the final exit status is 171 \fBnon-zero\fR. 172 .RE 173 174 .SH OPERANDS 175 The following operand is supported: 176 .sp 177 .ne 2 178 .na 179 \fB\fIfile\fR\fR 180 .ad 181 .RS 8n 182 A path name of a file to be compressed by \fBcompress\fR, uncompressed by 183 \fBuncompress\fR, or whose uncompressed form is written to standard out by 184 \fBzcat\fR. If \fIfile\fR is \fB\(mi\fR, or if no \fIfile\fR is specified, the 185 standard input is used. 186 .RE 187 188 .SH USAGE 189 See \fBlargefile\fR(5) for the description of the behavior of \fBcompress\fR, 190 \fBuncompress\fR, and \fBzcat\fR when encountering files greater than or equal 191 to 2 Gbyte (2^31 bytes). 192 .SH ENVIRONMENT VARIABLES 193 See \fBenviron\fR(5) for descriptions of the following environment variables 194 that affect the execution of \fBcompress\fR, \fBuncompress\fR, and \fBzcat\fR: 195 \fBLANG\fR, \fBLC_ALL\fR, \fBLC_COLLATE\fR, \fBLC_CTYPE\fR, \fBLC_MESSAGES\fR, 196 and \fBNLSPATH\fR. 197 .sp 198 .LP 199 Affirmative responses are processed using the extended regular expression 200 defined for the \fByesexpr\fR keyword in the \fBLC_MESSAGES\fR category of the 201 user's locale. The locale specified in the \fBLC_COLLATE\fR category defines 202 the behavior of ranges, equivalence classes, and multi-character collating 203 elements used in the expression defined for \fByesexpr\fR. The locale specified 204 in \fBLC_CTYPE\fR determines the locale for interpretation of sequences of 205 bytes of text data a characters, the behavior of character classes used in the 206 expression defined for the \fByesexpr\fR. See \fBlocale\fR(5). 207 .SH EXIT STATUS 208 The following error values are returned: 209 .sp 210 .ne 2 211 .na 212 \fB\fB0\fR\fR 213 .ad 214 .RS 6n 215 Successful completion. 216 .RE 217 218 .sp 219 .ne 2 220 .na 221 \fB\fB1\fR\fR 222 .ad 223 .RS 6n 224 An error occurred. 225 .RE 226 227 .sp 228 .ne 2 229 .na 230 \fB\fB2\fR\fR 231 .ad 232 .RS 6n 233 One or more files were not compressed because they would have increased in size 234 (and the \fB-f\fR option was not specified). 235 .RE 236 237 .sp 238 .ne 2 239 .na 240 \fB\fB>2\fR\fR 241 .ad 242 .RS 6n 243 An error occurred. 244 .RE 245 246 .SH ATTRIBUTES 247 See \fBattributes\fR(5) for descriptions of the following attributes: 248 .sp 249 250 .sp 251 .TS 252 box; 253 c | c 254 l | l . 255 ATTRIBUTE TYPE ATTRIBUTE VALUE 256 _ 257 CSI Enabled 258 _ 259 Interface Stability Committed 260 _ 261 Standard See \fBstandards\fR(5). 262 .TE 263 264 .SH SEE ALSO 265 \fBln\fR(1), \fBpack\fR(1), \fBfgetattr\fR(3C), \fBfsetattr\fR(3C), 266 \fBattributes\fR(5), \fBenviron\fR(5), \fBlargefile\fR(5), \fBlocale\fR(5), 267 \fBstandards\fR(5) 268 .SH DIAGNOSTICS 269 .ne 2 270 .na 271 \fBUsage: \fBcompress [-fv/] [-b\fR \fImaxbits\fR\fB]\fR [\fIfile\fR\|.\|.\|. ]\fR 272 .ad 273 .br 274 .na 275 \fB\fBcompress c [-fv] [-b\fR \fImaxbits\fR\fB]\fR [\fIfile\fR]\fR 276 .ad 277 .sp .6 278 .RS 4n 279 Invalid options were specified on the command line. 280 .RE 281 282 .sp 283 .ne 2 284 .na 285 \fBUsage: \fBuncompress [-fv] [-c | -/] [\fR\fIfile\fR\fB]...\fR\fR 286 .ad 287 .sp .6 288 .RS 4n 289 Invalid options were specified on the command line. 290 .RE 291 292 .sp 293 .ne 2 294 .na 295 \fBMissing maxbits\fR 296 .ad 297 .sp .6 298 .RS 4n 299 Maxbits must follow \fB-b\fR, or invalid maxbits, not a numeric value. 300 .RE 301 302 .sp 303 .ne 2 304 .na 305 \fB\fIfile\fR: not in compressed format\fR 306 .ad 307 .sp .6 308 .RS 4n 309 The file specified to \fBuncompress\fR has not been compressed. 310 .RE 311 312 .sp 313 .ne 2 314 .na 315 \fB\fIfile\fR: compressed with \fIxx\fRbits, can only handle \fIyy\fRbits\fR 316 .ad 317 .sp .6 318 .RS 4n 319 \fBfile\fR was compressed by a program that could deal with more \fIbits\fR 320 than the compress code on this machine. Recompress the file with smaller 321 \fIbits\fR. 322 .RE 323 324 .sp 325 .ne 2 326 .na 327 \fB\fIfile\fR: already has .\|Z suffix -- no change\fR 328 .ad 329 .sp .6 330 .RS 4n 331 The file is assumed to be already compressed. Rename the file and try again. 332 .RE 333 334 .sp 335 .ne 2 336 .na 337 \fB\fIfile\fR already exists; do you wish to overwrite (yes or no)?\fR 338 .ad 339 .sp .6 340 .RS 4n 341 Respond \fBy\fR if you want the output file to be replaced; \fBn\fR if not. 342 .RE 343 344 .sp 345 .ne 2 346 .na 347 \fBuncompress: corrupt input\fR 348 .ad 349 .sp .6 350 .RS 4n 351 A \fBSIGSEGV\fR violation was detected, which usually means that the input file 352 is corrupted. 353 .RE 354 355 .sp 356 .ne 2 357 .na 358 \fBCompression:\fIxx.xx\fR\fB%\fR\fR 359 .ad 360 .sp .6 361 .RS 4n 362 Percentage of the input saved by compression. (Relevant only for \fB-v\fR.) 363 .RE 364 365 .sp 366 .ne 2 367 .na 368 \fB- - not a regular file: unchanged\fR 369 .ad 370 .sp .6 371 .RS 4n 372 When the input file is not a regular file, (such as a directory), it is left 373 unaltered. 374 .RE 375 376 .sp 377 .ne 2 378 .na 379 \fB- - has \fIxx\fR other links: unchanged\fR 380 .ad 381 .sp .6 382 .RS 4n 383 The input file has links; it is left unchanged. See \fBln\fR(1) for more 384 information. 385 .RE 386 387 .sp 388 .ne 2 389 .na 390 \fB- - file unchanged\fR 391 .ad 392 .sp .6 393 .RS 4n 394 No savings are achieved by compression. The input remains uncompressed. 395 .RE 396 397 .sp 398 .ne 2 399 .na 400 \fB- -filename too long to tack on .Z\fR 401 .ad 402 .sp .6 403 .RS 4n 404 The path name is too long to append the \fB\&.Z\fR suffix. 405 .RE 406 407 .sp 408 .ne 2 409 .na 410 \fB- -cannot preserve extended attributes. file unchanged\fR 411 .ad 412 .sp .6 413 .RS 4n 414 Extended system attributes could not be copied. 415 .RE 416 417 .SH NOTES 418 Although compressed files are compatible between machines with large memory, 419 \fB-b\fR 12 should be used for file transfer to architectures with a small 420 process data space (64KB or less). 421 .sp 422 .LP 423 \fBcompress\fR should be more flexible about the existence of the \fB\&.\|Z\fR 424 suffix.