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talk.1p (10166B)


  1. '\" et
  2. .TH TALK "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. talk
  12. \(em talk to another user
  13. .SH SYNOPSIS
  14. .LP
  15. .nf
  16. talk \fIaddress \fB[\fIterminal\fB]\fR
  17. .fi
  18. .SH DESCRIPTION
  19. The
  20. .IR talk
  21. utility is a two-way, screen-oriented communication program.
  22. .P
  23. When first invoked,
  24. .IR talk
  25. shall send a message similar to:
  26. .sp
  27. .RS 4
  28. .nf
  29. Message from <\fIunspecified string\fP>
  30. talk: connection requested by \fIyour_address\fP
  31. talk: respond with: talk \fIyour_address\fP
  32. .fi
  33. .P
  34. .RE
  35. .P
  36. to the specified
  37. .IR address .
  38. At this point, the recipient of the message can reply by typing:
  39. .sp
  40. .RS 4
  41. .nf
  42. talk \fIyour_address\fR
  43. .fi
  44. .P
  45. .RE
  46. .P
  47. Once communication is established, the two parties can type
  48. simultaneously, with their output displayed in separate regions of the
  49. screen. Characters shall be processed as follows:
  50. .IP " *" 4
  51. Typing the
  52. <alert>
  53. character shall alert the recipient's terminal.
  54. .IP " *" 4
  55. Typing <control>\(hyL shall cause the sender's screen regions to be
  56. refreshed.
  57. .IP " *" 4
  58. Typing the erase and kill characters shall affect the sender's terminal
  59. in the manner described by the
  60. .BR termios
  61. interface in the Base Definitions volume of POSIX.1\(hy2017,
  62. .IR "Chapter 11" ", " "General Terminal Interface".
  63. .IP " *" 4
  64. Typing the interrupt or end-of-file characters shall terminate the
  65. local
  66. .IR talk
  67. utility. Once the
  68. .IR talk
  69. session has been terminated on one side, the other side of the
  70. .IR talk
  71. session shall be notified that the
  72. .IR talk
  73. session has been terminated and shall be able to do nothing except
  74. exit.
  75. .IP " *" 4
  76. Typing characters from
  77. .IR LC_CTYPE
  78. classifications
  79. .BR print
  80. or
  81. .BR space
  82. shall cause those characters to be sent to the recipient's terminal.
  83. .IP " *" 4
  84. When and only when the
  85. .IR stty
  86. .BR iexten
  87. local mode is enabled, the existence and processing of additional
  88. special control characters and multi-byte or single-byte functions
  89. shall be implementation-defined.
  90. .IP " *" 4
  91. Typing other non-printable characters shall cause
  92. implementation-defined sequences of printable characters to be sent
  93. to the recipient's terminal.
  94. .P
  95. Permission to be a recipient of a
  96. .IR talk
  97. message can be denied or granted by use of the
  98. .IR mesg
  99. utility. However, a user's privilege may further constrain the domain
  100. of accessibility of other users' terminals. The
  101. .IR talk
  102. utility shall fail when the user lacks appropriate privileges to
  103. perform the requested action.
  104. .P
  105. Certain block-mode terminals do not have all the capabilities necessary
  106. to support the simultaneous exchange of messages required for
  107. .IR talk .
  108. When this type of exchange cannot be supported on such terminals, the
  109. implementation may support an exchange with reduced levels of
  110. simultaneous interaction or it may report an error describing the
  111. terminal-related deficiency.
  112. .SH OPTIONS
  113. None.
  114. .SH OPERANDS
  115. The following operands shall be supported:
  116. .IP "\fIaddress\fR" 10
  117. The recipient of the
  118. .IR talk
  119. session. One form of
  120. .IR address
  121. is the <\fIuser\ name\fP>, as returned by the
  122. .IR who
  123. utility. Other address formats and how they are handled are
  124. unspecified.
  125. .IP "\fIterminal\fR" 10
  126. If the recipient is logged in more than once, the
  127. .IR terminal
  128. argument can be used to indicate the appropriate terminal name. If
  129. .IR terminal
  130. is not specified, the
  131. .IR talk
  132. message shall be displayed on one or more accessible terminals in use
  133. by the recipient. The format of
  134. .IR terminal
  135. shall be the same as that returned by the
  136. .IR who
  137. utility.
  138. .SH STDIN
  139. Characters read from standard input shall be copied to the recipient's
  140. terminal in an unspecified manner. If standard input is not a
  141. terminal, talk shall write a diagnostic message and exit with a
  142. non-zero status.
  143. .SH "INPUT FILES"
  144. None.
  145. .SH "ENVIRONMENT VARIABLES"
  146. The following environment variables shall affect the execution of
  147. .IR talk :
  148. .IP "\fILANG\fP" 10
  149. Provide a default value for the internationalization variables that are
  150. unset or null. (See the Base Definitions volume of POSIX.1\(hy2017,
  151. .IR "Section 8.2" ", " "Internationalization Variables"
  152. for the precedence of internationalization variables used to determine
  153. the values of locale categories.)
  154. .IP "\fILC_ALL\fP" 10
  155. If set to a non-empty string value, override the values of all the
  156. other internationalization variables.
  157. .IP "\fILC_CTYPE\fP" 10
  158. Determine the locale for the interpretation of sequences of bytes of
  159. text data as characters (for example, single-byte as opposed to
  160. multi-byte characters in arguments and input files). If the
  161. recipient's locale does not use an
  162. .IR LC_CTYPE
  163. equivalent to the sender's, the results are undefined.
  164. .IP "\fILC_MESSAGES\fP" 10
  165. .br
  166. Determine the locale that should be used to affect the format and
  167. contents of diagnostic messages written to standard error and
  168. informative messages written to standard output.
  169. .IP "\fINLSPATH\fP" 10
  170. Determine the location of message catalogs for the processing of
  171. .IR LC_MESSAGES .
  172. .IP "\fITERM\fP" 10
  173. Determine the name of the invoker's terminal type. If this variable is
  174. unset or null, an unspecified default terminal type shall be used.
  175. .SH "ASYNCHRONOUS EVENTS"
  176. When the
  177. .IR talk
  178. utility receives a SIGINT signal, the utility shall terminate and exit
  179. with a zero status. It shall take the standard action for all other
  180. signals.
  181. .SH STDOUT
  182. If standard output is a terminal, characters copied from the
  183. recipient's standard input may be written to standard output. Standard
  184. output also may be used for diagnostic messages. If standard output is
  185. not a terminal,
  186. .IR talk
  187. shall exit with a non-zero status.
  188. .SH STDERR
  189. None.
  190. .SH "OUTPUT FILES"
  191. None.
  192. .SH "EXTENDED DESCRIPTION"
  193. None.
  194. .SH "EXIT STATUS"
  195. The following exit values shall be returned:
  196. .IP "\00" 6
  197. Successful completion.
  198. .IP >0 6
  199. An error occurred or
  200. .IR talk
  201. was invoked on a terminal incapable of supporting it.
  202. .SH "CONSEQUENCES OF ERRORS"
  203. Default.
  204. .LP
  205. .IR "The following sections are informative."
  206. .SH "APPLICATION USAGE"
  207. Because the handling of non-printable, non-\c
  208. <space>
  209. characters is tied to the
  210. .IR stty
  211. description of
  212. .BR iexten ,
  213. implementation extensions within the terminal driver can be accessed.
  214. For example, some implementations provide line editing functions with
  215. certain control character sequences.
  216. .SH EXAMPLES
  217. None.
  218. .SH RATIONALE
  219. The
  220. .IR write
  221. utility was included in this volume of POSIX.1\(hy2017 since it can be implemented on all
  222. terminal types. The
  223. .IR talk
  224. utility, which cannot be implemented on certain terminals, was
  225. considered to be a ``better'' communications interface. Both of these
  226. programs are in widespread use on historical implementations.
  227. Therefore, both utilities have been specified.
  228. .P
  229. All references to networking abilities (\fItalk\fPing to a user on
  230. another system) were removed as being outside the scope of this volume of POSIX.1\(hy2017.
  231. .P
  232. Historical BSD and System V versions of
  233. .IR talk
  234. terminate both of the conversations when either user breaks out of the
  235. session. This can lead to adverse consequences if a user unwittingly
  236. continues to enter text that is interpreted by the shell when the other
  237. terminates the session. Therefore, the version of
  238. .IR talk
  239. specified by this volume of POSIX.1\(hy2017 requires both users to terminate their end of the
  240. session explicitly.
  241. .P
  242. Only messages sent to the terminal of the invoking user can be
  243. internationalized in any way:
  244. .IP " *" 4
  245. The original ``Message from <\fIunspecified string\fP> .\|.\|.''
  246. message sent to the terminal of the recipient cannot be
  247. internationalized because the environment of the recipient is as yet
  248. inaccessible to the
  249. .IR talk
  250. utility. The environment of the invoking party is irrelevant.
  251. .IP " *" 4
  252. Subsequent communication between the two parties cannot be
  253. internationalized because the two parties may specify different
  254. languages in their environment (and non-portable characters cannot be
  255. mapped from one language to another).
  256. .IP " *" 4
  257. Neither party can be required to communicate in a language other than C
  258. and/or the one specified by their environment because unavailable
  259. terminal hardware support (for example, fonts) may be required.
  260. .P
  261. The text in the STDOUT section reflects the usage of the verb
  262. ``display'' in this section; some
  263. .IR talk
  264. implementations actually use standard output to write to the terminal,
  265. but this volume of POSIX.1\(hy2017 does not require that to be the case.
  266. .P
  267. The format of the terminal name is unspecified, but the descriptions of
  268. .IR ps ,
  269. .IR talk ,
  270. .IR who ,
  271. and
  272. .IR write
  273. require that they all use or accept the same format.
  274. .P
  275. The handling of non-printable characters is partially
  276. implementation-defined
  277. because the details of mapping them to printable sequences is not
  278. needed by the user. Historical implementations, for security reasons,
  279. disallow the transmission of non-printable characters that may send
  280. commands to the other terminal.
  281. .SH "FUTURE DIRECTIONS"
  282. None.
  283. .SH "SEE ALSO"
  284. .IR "\fImesg\fR\^",
  285. .IR "\fIstty\fR\^",
  286. .IR "\fIwho\fR\^",
  287. .IR "\fIwrite\fR\^"
  288. .P
  289. The Base Definitions volume of POSIX.1\(hy2017,
  290. .IR "Chapter 8" ", " "Environment Variables",
  291. .IR "Chapter 11" ", " "General Terminal Interface"
  292. .\"
  293. .SH COPYRIGHT
  294. Portions of this text are reprinted and reproduced in electronic form
  295. from IEEE Std 1003.1-2017, Standard for Information Technology
  296. -- Portable Operating System Interface (POSIX), The Open Group Base
  297. Specifications Issue 7, 2018 Edition,
  298. Copyright (C) 2018 by the Institute of
  299. Electrical and Electronics Engineers, Inc and The Open Group.
  300. In the event of any discrepancy between this version and the original IEEE and
  301. The Open Group Standard, the original IEEE and The Open Group Standard
  302. is the referee document. The original Standard can be obtained online at
  303. http://www.opengroup.org/unix/online.html .
  304. .PP
  305. Any typographical or formatting errors that appear
  306. in this page are most likely
  307. to have been introduced during the conversion of the source files to
  308. man page format. To report such errors, see
  309. https://www.kernel.org/doc/man-pages/reporting_bugs.html .