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dd.1p (21634B)


  1. '\" et
  2. .TH DD "1P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual"
  3. .\"
  4. .SH PROLOG
  5. This manual page is part of the POSIX Programmer's Manual.
  6. The Linux implementation of this interface may differ (consult
  7. the corresponding Linux manual page for details of Linux behavior),
  8. or the interface may not be implemented on Linux.
  9. .\"
  10. .SH NAME
  11. dd
  12. \(em convert and copy a file
  13. .SH SYNOPSIS
  14. .LP
  15. .nf
  16. dd \fB[\fIoperand\fR...\fB]\fR
  17. .fi
  18. .SH DESCRIPTION
  19. The
  20. .IR dd
  21. utility shall copy the specified input file to the specified output
  22. file with possible conversions using specific input and output block
  23. sizes. It shall read the input one block at a time, using the
  24. specified input block size; it shall then process the block of data
  25. actually returned, which could be smaller than the requested block
  26. size. It shall apply any conversions that have been specified and write
  27. the resulting data to the output in blocks of the specified output
  28. block size. If the
  29. .BR bs =\c
  30. .IR expr
  31. operand is specified and no conversions other than
  32. .BR sync ,
  33. .BR noerror ,
  34. or
  35. .BR notrunc
  36. are requested, the data returned from each input block shall be written
  37. as a separate output block; if the read returns less than a full block
  38. and the
  39. .BR sync
  40. conversion is not specified, the resulting output block shall be the
  41. same size as the input block. If the
  42. .BR bs =\c
  43. .IR expr
  44. operand is not specified, or a conversion other than
  45. .BR sync ,
  46. .BR noerror ,
  47. or
  48. .BR notrunc
  49. is requested, the input shall be processed and collected into
  50. full-sized output blocks until the end of the input is reached.
  51. .P
  52. The processing order shall be as follows:
  53. .IP " 1." 4
  54. An input block is read.
  55. .IP " 2." 4
  56. If the input block is shorter than the specified input block size and
  57. the
  58. .BR sync
  59. conversion is specified, null bytes shall be appended to the input data
  60. up to the specified size. (If either
  61. .BR block
  62. or
  63. .BR unblock
  64. is also specified,
  65. <space>
  66. characters shall be appended instead of null bytes.) The remaining
  67. conversions and output shall include the pad characters as if they had
  68. been read from the input.
  69. .IP " 3." 4
  70. If the
  71. .BR bs =\c
  72. .IR expr
  73. operand is specified and no conversion other than
  74. .BR sync
  75. or
  76. .BR noerror
  77. is requested, the resulting data shall be written to the output as a
  78. single block, and the remaining steps are omitted.
  79. .IP " 4." 4
  80. If the
  81. .BR swab
  82. conversion is specified, each pair of input data bytes shall be
  83. swapped. If there is an odd number of bytes in the input block, the
  84. last byte in the input record shall not be swapped.
  85. .IP " 5." 4
  86. Any remaining conversions (\c
  87. .BR block ,
  88. .BR unblock ,
  89. .BR lcase ,
  90. and
  91. .BR ucase )
  92. shall be performed. These conversions shall operate on the input data
  93. independently of the input blocking; an input or output fixed-length
  94. record may span block boundaries.
  95. .IP " 6." 4
  96. The data resulting from input or conversion or both shall be aggregated
  97. into output blocks of the specified size. After the end of input is
  98. reached, any remaining output shall be written as a block without
  99. padding if
  100. .BR conv =\c
  101. .BR sync
  102. is not specified; thus, the final output block may be shorter than the
  103. output block size.
  104. .SH OPTIONS
  105. None.
  106. .SH OPERANDS
  107. All of the operands shall be processed before any input is read.
  108. The following operands shall be supported:
  109. .IP "\fBif\fR=\fIfile\fR" 10
  110. Specify the input pathname; the default is standard input.
  111. .IP "\fBof\fR=\fIfile\fR" 10
  112. Specify the output pathname; the default is standard output. If the
  113. .BR seek =\c
  114. .IR expr
  115. conversion is not also specified, the output file shall be truncated
  116. before the copy begins if an explicit
  117. .BR of =\c
  118. .IR file
  119. operand is specified, unless
  120. .BR conv =\c
  121. .BR notrunc
  122. is specified. If
  123. .BR seek =\c
  124. .IR expr
  125. is specified, but
  126. .BR conv =\c
  127. .BR notrunc
  128. is not, the effect of the copy shall be to preserve the blocks in the
  129. output file over which
  130. .IR dd
  131. seeks, but no other portion of the output file shall be preserved. (If
  132. the size of the seek plus the size of the input file is less than the
  133. previous size of the output file, the output file shall be shortened by
  134. the copy. If the input file is empty and either the size of the seek is
  135. greater than the previous size of the output file or the output file
  136. did not previously exist, the size of the output file shall be set to
  137. the file offset after the seek.)
  138. .IP "\fBibs\fR=\fIexpr\fR" 10
  139. Specify the input block size, in bytes, by
  140. .IR expr
  141. (default is 512).
  142. .IP "\fBobs\fR=\fIexpr\fR" 10
  143. Specify the output block size, in bytes, by
  144. .IR expr
  145. (default is 512).
  146. .IP "\fBbs\fR=\fIexpr\fR" 10
  147. Set both input and output block sizes to
  148. .IR expr
  149. bytes, superseding
  150. .BR ibs =
  151. and
  152. .BR obs =.
  153. If no conversion other than
  154. .BR sync ,
  155. .BR noerror ,
  156. and
  157. .BR notrunc
  158. is specified, each input block shall be copied to the output as a
  159. single block without aggregating short blocks.
  160. .IP "\fBcbs\fR=\fIexpr\fR" 10
  161. Specify the conversion block size for
  162. .BR block
  163. and
  164. .BR unblock
  165. in bytes by
  166. .IR expr
  167. (default is zero). If
  168. .BR cbs =
  169. is omitted or given a value of zero, using
  170. .BR block
  171. or
  172. .BR unblock
  173. produces unspecified results.
  174. .RS 10
  175. .P
  176. The application shall ensure that this operand is also specified if the
  177. .BR conv =
  178. operand is specified with a value of
  179. .BR ascii ,
  180. .BR ebcdic ,
  181. or
  182. .BR ibm .
  183. For a
  184. .BR conv =
  185. operand with an
  186. .BR ascii
  187. value, the input is handled as described for the
  188. .BR unblock
  189. value, except that characters are converted to ASCII before any
  190. trailing
  191. <space>
  192. characters are deleted. For
  193. .BR conv =
  194. operands with
  195. .BR ebcdic
  196. or
  197. .BR ibm
  198. values, the input is handled as described for the
  199. .BR block
  200. value except that the characters are converted to EBCDIC or IBM EBCDIC,
  201. respectively, after any trailing
  202. <space>
  203. characters are added.
  204. .RE
  205. .IP "\fBskip\fR=\fIn\fR" 10
  206. Skip
  207. .IR n
  208. input blocks (using the specified input block size) before starting to
  209. copy. On seekable files, the implementation shall read the blocks or
  210. seek past them; on non-seekable files, the blocks shall be read and the
  211. data shall be discarded.
  212. .IP "\fBseek\fR=\fIn\fR" 10
  213. Skip
  214. .IR n
  215. blocks (using the specified output block size) from the beginning of the
  216. output file before copying. On non-seekable files, existing blocks
  217. shall be read and space from the current end-of-file to the specified
  218. offset, if any, filled with null bytes; on seekable files, the
  219. implementation shall seek to the specified offset or read the blocks as
  220. described for non-seekable files.
  221. .IP "\fBcount\fR=\fIn\fR" 10
  222. Copy only
  223. .IR n
  224. input blocks. If
  225. .IR n
  226. is zero, it is unspecified whether no blocks or all blocks are copied.
  227. .IP "\fBconv\fR=\fIvalue\fB[\fR,\fIvalue\fR\ .\|.\|.\fB]\fR" 10
  228. .br
  229. Where
  230. .IR value s
  231. are
  232. <comma>-separated
  233. symbols from the following list:
  234. .RS 10
  235. .IP "\fBascii\fR" 9
  236. Convert EBCDIC to ASCII; see
  237. .IR "Table 4-7, ASCII to EBCDIC Conversion".
  238. .IP "\fBebcdic\fR" 9
  239. Convert ASCII to EBCDIC; see
  240. .IR "Table 4-7, ASCII to EBCDIC Conversion".
  241. .IP "\fBibm\fR" 9
  242. Convert ASCII to a different EBCDIC set; see
  243. .IR "Table 4-8, ASCII to IBM EBCDIC Conversion".
  244. .P
  245. The
  246. .BR ascii ,
  247. .BR ebcdic ,
  248. and
  249. .BR ibm
  250. values are mutually-exclusive.
  251. .IP "\fBblock\fR" 9
  252. Treat the input as a sequence of
  253. <newline>-terminated
  254. or end-of-file-terminated variable-length records independent of the
  255. input block boundaries. Each record shall be converted to a record with
  256. a fixed length specified by the conversion block size. Any
  257. <newline>
  258. shall be removed from the input line;
  259. <space>
  260. characters shall be appended to lines that are shorter than their
  261. conversion block size to fill the block. Lines that are longer than
  262. the conversion block size shall be truncated to the largest number of
  263. characters that fit into that size; the number of truncated lines shall
  264. be reported (see the STDERR section).
  265. .RS 9
  266. .P
  267. The
  268. .BR block
  269. and
  270. .BR unblock
  271. values are mutually-exclusive.
  272. .RE
  273. .IP "\fBunblock\fR" 9
  274. Convert fixed-length records to variable length. Read a number of bytes
  275. equal to the conversion block size (or the number of bytes remaining in
  276. the input, if less than the conversion block size), delete all trailing
  277. <space>
  278. characters, and append a
  279. <newline>.
  280. .IP "\fBlcase\fR" 9
  281. Map uppercase characters specified by the
  282. .IR LC_CTYPE
  283. keyword
  284. .BR tolower
  285. to the corresponding lowercase character. Characters for which no
  286. mapping is specified shall not be modified by this conversion.
  287. .RS 9
  288. .P
  289. The
  290. .BR lcase
  291. and
  292. .BR ucase
  293. symbols are mutually-exclusive.
  294. .RE
  295. .IP "\fBucase\fR" 9
  296. Map lowercase characters specified by the
  297. .IR LC_CTYPE
  298. keyword
  299. .BR toupper
  300. to the corresponding uppercase character. Characters for which no
  301. mapping is specified shall not be modified by this conversion.
  302. .IP "\fBswab\fR" 9
  303. Swap every pair of input bytes.
  304. .IP "\fBnoerror\fR" 9
  305. Do not stop processing on an input error. When an input error occurs, a
  306. diagnostic message shall be written on standard error, followed by the
  307. current input and output block counts in the same format as used at
  308. completion (see the STDERR section). If the
  309. .BR sync
  310. conversion is specified, the missing input shall be replaced with null
  311. bytes and processed normally; otherwise, the input block shall be
  312. omitted from the output.
  313. .IP "\fBnotrunc\fR" 9
  314. Do not truncate the output file. Preserve blocks in the output
  315. file not explicitly written by this invocation of the
  316. .IR dd
  317. utility. (See also the preceding
  318. .BR of =\c
  319. .IR file
  320. operand.)
  321. .IP "\fBsync\fR" 9
  322. Pad every input block to the size of the
  323. .BR ibs =
  324. buffer, appending null bytes. (If either
  325. .BR block
  326. or
  327. .BR unblock
  328. is also specified, append
  329. <space>
  330. characters, rather than null bytes.)
  331. .RE
  332. .P
  333. The behavior is unspecified if operands other than
  334. .BR conv =
  335. are specified more than once.
  336. .P
  337. For the
  338. .BR bs =,
  339. .BR cbs =,
  340. .BR ibs =,
  341. and
  342. .BR obs =
  343. operands, the application shall supply an expression specifying a size
  344. in bytes. The expression,
  345. .IR expr ,
  346. can be:
  347. .IP " 1." 4
  348. A positive decimal number
  349. .IP " 2." 4
  350. A positive decimal number followed by
  351. .IR k ,
  352. specifying multiplication by 1\|024
  353. .IP " 3." 4
  354. A positive decimal number followed by
  355. .IR b ,
  356. specifying multiplication by 512
  357. .IP " 4." 4
  358. Two or more positive decimal numbers (with or without
  359. .IR k
  360. or
  361. .IR b )
  362. separated by
  363. .IR x ,
  364. specifying the product of the indicated values
  365. .P
  366. All of the operands are processed before any input is read.
  367. .P
  368. The following two tables display the octal number character values used
  369. for the
  370. .BR ascii
  371. and
  372. .BR ebcdic
  373. conversions (first table) and for the
  374. .BR ibm
  375. conversion (second table). In both tables, the ASCII values are the row
  376. and column headers and the EBCDIC values are found at their
  377. intersections. For example, ASCII 0012 (LF) is the second row, third
  378. column, yielding 0045 in EBCDIC. The inverted tables (for EBCDIC to
  379. ASCII conversion) are not shown, but are in one-to-one correspondence
  380. with these tables. The differences between the two tables are
  381. highlighted by small boxes drawn around five entries.
  382. .br
  383. .sp
  384. .ce 1
  385. \fBTable 4-7: ASCII to EBCDIC Conversion\fR
  386. .bp
  387. .sp
  388. .ce 1
  389. \fBTable 4-8: ASCII to IBM EBCDIC Conversion\fR
  390. .SH STDIN
  391. If no
  392. .BR if =
  393. operand is specified, the standard input shall be used. See the INPUT
  394. FILES section.
  395. .SH "INPUT FILES"
  396. The input file can be any file type.
  397. .SH "ENVIRONMENT VARIABLES"
  398. The following environment variables shall affect the execution of
  399. .IR dd :
  400. .IP "\fILANG\fP" 10
  401. Provide a default value for the internationalization variables that are
  402. unset or null. (See the Base Definitions volume of POSIX.1\(hy2017,
  403. .IR "Section 8.2" ", " "Internationalization Variables"
  404. for the precedence of internationalization variables used to determine
  405. the values of locale categories.)
  406. .IP "\fILC_ALL\fP" 10
  407. If set to a non-empty string value, override the values of all the
  408. other internationalization variables.
  409. .IP "\fILC_CTYPE\fP" 10
  410. Determine the locale for the interpretation of sequences of bytes of
  411. text data as characters (for example, single-byte as opposed to
  412. multi-byte characters in arguments and input files), the classification
  413. of characters as uppercase or lowercase, and the mapping of characters
  414. from one case to the other.
  415. .IP "\fILC_MESSAGES\fP" 10
  416. .br
  417. Determine the locale that should be used to affect the format and
  418. contents of diagnostic messages written to standard error and
  419. informative messages written to standard output.
  420. .IP "\fINLSPATH\fP" 10
  421. Determine the location of message catalogs for the processing of
  422. .IR LC_MESSAGES .
  423. .SH "ASYNCHRONOUS EVENTS"
  424. For SIGINT, the
  425. .IR dd
  426. utility shall interrupt its current processing, write status
  427. information to standard error, and exit as though terminated by
  428. SIGINT. It shall take the standard action for all other signals; see
  429. the ASYNCHRONOUS EVENTS section in
  430. .IR "Section 1.4" ", " "Utility Description Defaults".
  431. .SH STDOUT
  432. If no
  433. .BR of =
  434. operand is specified, the standard output shall be used. The nature of
  435. the output depends on the operands selected.
  436. .SH STDERR
  437. On completion,
  438. .IR dd
  439. shall write the number of input and output blocks to standard error. In
  440. the POSIX locale the following formats shall be used:
  441. .sp
  442. .RS 4
  443. .nf
  444. "%u+%u records in\en", <\fInumber of whole input blocks\fR>,
  445. <\fInumber of partial input blocks\fR>
  446. .P
  447. "%u+%u records out\en", <\fInumber of whole output blocks\fR>,
  448. <\fInumber of partial output blocks\fR>
  449. .fi
  450. .P
  451. .RE
  452. .P
  453. A partial input block is one for which
  454. \fIread\fR()
  455. returned less than the input block size. A partial output block is one
  456. that was written with fewer bytes than specified by the output block
  457. size.
  458. .P
  459. In addition, when there is at least one truncated block, the number of
  460. truncated blocks shall be written to standard error. In the POSIX
  461. locale, the format shall be:
  462. .sp
  463. .RS 4
  464. .nf
  465. "%u truncated %s\en", <\fInumber of truncated blocks\fR>, "record" (if
  466. <\fInumber of truncated blocks\fR> is one) "records" (otherwise)
  467. .fi
  468. .P
  469. .RE
  470. .P
  471. Diagnostic messages may also be written to standard error.
  472. .SH "OUTPUT FILES"
  473. If the
  474. .BR of =
  475. operand is used, the output shall be the same as described in the
  476. STDOUT section.
  477. .SH "EXTENDED DESCRIPTION"
  478. None.
  479. .SH "EXIT STATUS"
  480. The following exit values shall be returned:
  481. .IP "\00" 6
  482. The input file was copied successfully.
  483. .IP >0 6
  484. An error occurred.
  485. .SH "CONSEQUENCES OF ERRORS"
  486. If an input error is detected and the
  487. .BR noerror
  488. conversion has not been specified, any partial output block shall be
  489. written to the output file, a diagnostic message shall be written, and
  490. the copy operation shall be discontinued. If some other error is
  491. detected, a diagnostic message shall be written and the copy operation
  492. shall be discontinued.
  493. .LP
  494. .IR "The following sections are informative."
  495. .SH "APPLICATION USAGE"
  496. The input and output block size can be specified to take advantage of
  497. raw physical I/O.
  498. .P
  499. There are many different versions of the EBCDIC codesets. The ASCII and
  500. EBCDIC conversions specified for the
  501. .IR dd
  502. utility perform conversions for the version specified by the tables.
  503. .SH EXAMPLES
  504. The following command:
  505. .sp
  506. .RS 4
  507. .nf
  508. dd if=/dev/rmt0h of=/dev/rmt1h
  509. .fi
  510. .P
  511. .RE
  512. .P
  513. copies from tape drive 0 to tape drive 1, using a common historical
  514. device naming convention.
  515. .P
  516. The following command:
  517. .sp
  518. .RS 4
  519. .nf
  520. dd ibs=10 skip=1
  521. .fi
  522. .P
  523. .RE
  524. .P
  525. strips the first 10 bytes from standard input.
  526. .P
  527. This example reads an EBCDIC tape blocked ten 80-byte EBCDIC card
  528. images per block into the ASCII file
  529. .BR x :
  530. .sp
  531. .RS 4
  532. .nf
  533. dd if=/dev/tape of=x ibs=800 cbs=80 conv=ascii,lcase
  534. .fi
  535. .P
  536. .RE
  537. .SH RATIONALE
  538. The OPTIONS section is listed as ``None'' because there are no options
  539. recognized by historical
  540. .IR dd
  541. utilities. Certainly, many of the operands could have been designed to
  542. use the Utility Syntax Guidelines, which would have resulted in the
  543. classic hyphenated option letters. In this version of this volume of POSIX.1\(hy2017,
  544. .IR dd
  545. retains its curious JCL-like syntax due to the large number of
  546. applications that depend on the historical implementation.
  547. .P
  548. A suggested implementation technique for
  549. .BR conv =\c
  550. .BR noerror ,\c
  551. .BR sync
  552. is to zero (or
  553. <space>-fill,
  554. if
  555. .BR block ing
  556. or
  557. .BR unblock ing)
  558. the input buffer before each read and to write the contents of the
  559. input buffer to the output even after an error. In this manner, any
  560. data transferred to the input buffer before the error was detected is
  561. preserved. Another point is that a failed read on a regular file or a
  562. disk generally does not increment the file offset, and
  563. .IR dd
  564. must then seek past the block on which the error occurred; otherwise,
  565. the input error occurs repetitively. When the input is a magnetic tape,
  566. however, the tape normally has passed the block containing the error
  567. when the error is reported, and thus no seek is necessary.
  568. .P
  569. The default
  570. .BR ibs =
  571. and
  572. .BR obs =
  573. sizes are specified as 512 bytes because there are historical (largely
  574. portable) scripts that assume these values. If they were left
  575. unspecified, unusual results could occur if an implementation chose an
  576. odd block size.
  577. .P
  578. Historical implementations of
  579. .IR dd
  580. used
  581. \fIcreat\fR()
  582. when processing
  583. .BR of =\c
  584. .IR file .
  585. This makes the
  586. .BR seek =
  587. operand unusable except on special files. The
  588. .BR conv =\c
  589. .BR notrunc
  590. feature was added because more recent BSD-based implementations use
  591. \fIopen\fR()
  592. (without O_TRUNC) instead of
  593. \fIcreat\fR(),
  594. but they fail to delete output file contents after the data copied.
  595. .P
  596. The
  597. .IR w
  598. multiplier (historically meaning
  599. .IR word ),
  600. is used in System V to mean 2 and in 4.2 BSD to mean 4. Since
  601. .IR word
  602. is inherently non-portable, its use is not supported by this volume of POSIX.1\(hy2017.
  603. .P
  604. Standard EBCDIC does not have the characters
  605. .BR '['
  606. and
  607. .BR ']' .
  608. The values used in the table are taken from a common print train that
  609. does contain them. Other than those characters, the print train values
  610. are not filled in, but appear to provide some of the motivation for the
  611. historical choice of translations reflected here.
  612. .P
  613. The Standard EBCDIC table provides a 1:1 translation for all 256
  614. bytes.
  615. .P
  616. The IBM EBCDIC table does not provide such a translation. The marked
  617. cells in the tables differ in such a way that:
  618. .IP " 1." 4
  619. EBCDIC 0112 (\c
  620. .BR '\(ct' )
  621. and 0152 (broken pipe) do not appear in the table.
  622. .IP " 2." 4
  623. EBCDIC 0137 (\c
  624. .BR '\(no' )
  625. translates to/from ASCII 0236 (\c
  626. .BR '\(ha' ).
  627. In the standard table, EBCDIC 0232 (no graphic) is used.
  628. .IP " 3." 4
  629. EBCDIC 0241 (\c
  630. .BR '\(ti' )
  631. translates to/from ASCII 0176 (\c
  632. .BR '\(ti' ).
  633. In the standard table, EBCDIC 0137 (\c
  634. .BR '\(no' )
  635. is used.
  636. .IP " 4." 4
  637. 0255 (\c
  638. .BR '[' )
  639. and 0275 (\c
  640. .BR ']' )
  641. appear twice, once in the same place as for the standard table and once
  642. in place of 0112 (\c
  643. .BR '\(ct' )
  644. and 0241 (\c
  645. .BR '\(ti' ).
  646. .P
  647. In net result:
  648. .sp
  649. .RS
  650. EBCDIC 0275 (\c
  651. .BR ']' )
  652. displaced EBCDIC 0241 (\c
  653. .BR '\(ti' )
  654. in cell 0345.
  655. .P
  656. \0\0\0\0That displaced EBCDIC 0137 (\c
  657. .BR '\(no' )
  658. in cell 0176.
  659. .P
  660. \0\0\0\0That displaced EBCDIC 0232 (no graphic) in cell 0136.
  661. .P
  662. \0\0\0\0That replaced EBCDIC 0152 (broken pipe) in cell 0313.
  663. .P
  664. EBCDIC 0255 (\c
  665. .BR '[' )
  666. replaced EBCDIC 0112 (\c
  667. .BR '\(ct' ).
  668. .RE
  669. .P
  670. This translation, however, reflects historical practice that (ASCII)
  671. .BR '\(ti'
  672. and
  673. .BR '\(no'
  674. were often mapped to each other, as were
  675. .BR '['
  676. and
  677. .BR '\(ct' ;
  678. and
  679. .BR ']'
  680. and (EBCDIC)
  681. .BR '\(ti' .
  682. .P
  683. The
  684. .BR cbs
  685. operand is required if any of the
  686. .BR ascii ,
  687. .BR ebcdic ,
  688. or
  689. .BR ibm
  690. operands are specified. For the
  691. .BR ascii
  692. operand, the input is handled as described for the
  693. .BR unblock
  694. operand except that characters are converted to ASCII before the
  695. trailing
  696. <space>
  697. characters are deleted. For the
  698. .BR ebcdic
  699. and
  700. .BR ibm
  701. operands, the input is handled as described for the
  702. .BR block
  703. operand except that the characters are converted to EBCDIC or IBM
  704. EBCDIC after the trailing
  705. <space>
  706. characters are added.
  707. .P
  708. The
  709. .BR block
  710. and
  711. .BR unblock
  712. keywords are from historical BSD practice.
  713. .P
  714. The consistent use of the word
  715. .BR record
  716. in standard error messages matches most historical practice. An
  717. earlier version of System V used
  718. .BR block ,
  719. but this has been updated in more recent releases.
  720. .P
  721. Early proposals only allowed two numbers separated by
  722. .BR x
  723. to be used in a product when specifying
  724. .BR bs =,
  725. .BR cbs =,
  726. .BR ibs =,
  727. and
  728. .BR obs =
  729. sizes. This was changed to reflect the historical practice of allowing
  730. multiple numbers in the product as provided by Version 7 and all
  731. releases of System V and BSD.
  732. .P
  733. A change to the
  734. .BR swab
  735. conversion is required to match historical practice and is the result
  736. of IEEE PASC Interpretations 1003.2 #03 and #04, submitted for the
  737. ISO\ POSIX\(hy2:\|1993 standard.
  738. .P
  739. A change to the handling of SIGINT is required to match historical
  740. practice and is the result of IEEE PASC Interpretation 1003.2 #06
  741. submitted for the ISO\ POSIX\(hy2:\|1993 standard.
  742. .SH "FUTURE DIRECTIONS"
  743. None.
  744. .SH "SEE ALSO"
  745. .IR "Section 1.4" ", " "Utility Description Defaults",
  746. .IR "\fIsed\fR\^",
  747. .IR "\fItr\fR\^"
  748. .P
  749. The Base Definitions volume of POSIX.1\(hy2017,
  750. .IR "Chapter 8" ", " "Environment Variables"
  751. .\"
  752. .SH COPYRIGHT
  753. Portions of this text are reprinted and reproduced in electronic form
  754. from IEEE Std 1003.1-2017, Standard for Information Technology
  755. -- Portable Operating System Interface (POSIX), The Open Group Base
  756. Specifications Issue 7, 2018 Edition,
  757. Copyright (C) 2018 by the Institute of
  758. Electrical and Electronics Engineers, Inc and The Open Group.
  759. In the event of any discrepancy between this version and the original IEEE and
  760. The Open Group Standard, the original IEEE and The Open Group Standard
  761. is the referee document. The original Standard can be obtained online at
  762. http://www.opengroup.org/unix/online.html .
  763. .PP
  764. Any typographical or formatting errors that appear
  765. in this page are most likely
  766. to have been introduced during the conversion of the source files to
  767. man page format. To report such errors, see
  768. https://www.kernel.org/doc/man-pages/reporting_bugs.html .