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unset.1p (4052B)

    

  1. '\" et
  2. .TH UNSET "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. unset
  12. \(em unset values and attributes of variables and functions
  13. .SH SYNOPSIS
  14. .LP
  15. .nf
  16. unset \fB[\fR-fv\fB] \fIname\fR...
  17. .fi
  18. .SH DESCRIPTION
  19. Each variable or function specified by
  20. .IR name
  21. shall be unset.
  22. .P
  23. If
  24. .BR \-v
  25. is specified,
  26. .IR name
  27. refers to a variable name and the shell shall unset it and remove it
  28. from the environment. Read-only variables cannot be unset.
  29. .P
  30. If
  31. .BR \-f
  32. is specified,
  33. .IR name
  34. refers to a function and the shell shall unset the function definition.
  35. .P
  36. If neither
  37. .BR \-f
  38. nor
  39. .BR \-v
  40. is specified,
  41. .IR name
  42. refers to a variable; if a variable by that name does not exist, it is
  43. unspecified whether a function by that name, if any, shall be unset.
  44. .P
  45. Unsetting a variable or function that was not previously set shall not
  46. be considered an error and does not cause the shell to abort.
  47. .P
  48. The
  49. .IR unset
  50. special built-in shall support the Base Definitions volume of POSIX.1\(hy2017,
  51. .IR "Section 12.2" ", " "Utility Syntax Guidelines".
  52. .P
  53. Note that:
  54. .sp
  55. .RS 4
  56. .nf
  58. VARIABLE=
  59. .fi
  60. .P
  61. .RE
  62. .P
  63. is not equivalent to an
  64. .IR unset
  65. of
  66. .BR VARIABLE ;
  67. in the example,
  68. .BR VARIABLE
  69. is set to
  70. .BR \(dq\^\(dq .
  71. Also, the variables that can be
  72. .IR unset
  73. should not be misinterpreted to include the special parameters (see
  74. .IR "Section 2.5.2" ", " "Special Parameters").
  75. .SH OPTIONS
  76. See the DESCRIPTION.
  77. .SH OPERANDS
  78. See the DESCRIPTION.
  79. .SH STDIN
  80. Not used.
  81. .SH "INPUT FILES"
  82. None.
  83. .SH "ENVIRONMENT VARIABLES"
  84. None.
  85. .SH "ASYNCHRONOUS EVENTS"
  86. Default.
  87. .SH STDOUT
  88. Not used.
  89. .SH STDERR
  90. The standard error shall be used only for diagnostic messages.
  91. .SH "OUTPUT FILES"
  92. None.
  93. .SH "EXTENDED DESCRIPTION"
  94. None.
  95. .SH "EXIT STATUS"
  96. .IP "\00" 6
  97. All
  98. .IR name
  99. operands were successfully unset.
  100. .IP >0 6
  101. At least one
  102. .IR name
  103. could not be unset.
  104. .SH "CONSEQUENCES OF ERRORS"
  105. Default.
  106. .LP
  107. .IR "The following sections are informative."
  108. .SH "APPLICATION USAGE"
  109. None.
  110. .SH EXAMPLES
  111. Unset
  112. .IR VISUAL
  113. variable:
  114. .sp
  115. .RS 4
  116. .nf
  118. unset -v VISUAL
  119. .fi
  120. .P
  121. .RE
  122. .P
  123. Unset the functions
  124. .BR foo
  125. and
  126. .BR bar :
  127. .sp
  128. .RS 4
  129. .nf
  131. unset -f foo bar
  132. .fi
  133. .P
  134. .RE
  135. .SH "RATIONALE"
  136. Consideration was given to omitting the
  137. .BR \-f
  138. option in favor of an
  139. .IR unfunction
  140. utility, but the standard developers decided to retain historical
  141. practice.
  142. .P
  143. The
  144. .BR \-v
  145. option was introduced because System V historically used one name space
  146. for both variables and functions. When
  147. .IR unset
  148. is used without options, System V historically unset either a function
  149. or a variable, and there was no confusion about which one was intended.
  150. A portable POSIX application can use
  151. .IR unset
  152. without an option to unset a variable, but not a function; the
  153. .BR \-f
  154. option must be used.
  155. .SH "FUTURE DIRECTIONS"
  156. None.
  157. .SH "SEE ALSO"
  158. .IR "Section 2.14" ", " "Special Built-In Utilities"
  159. .P
  160. The Base Definitions volume of POSIX.1\(hy2017,
  161. .IR "Section 12.2" ", " "Utility Syntax Guidelines"
  162. .\"
  163. .SH COPYRIGHT
  164. Portions of this text are reprinted and reproduced in electronic form
  165. from IEEE Std 1003.1-2017, Standard for Information Technology
  166. -- Portable Operating System Interface (POSIX), The Open Group Base
  167. Specifications Issue 7, 2018 Edition,
  168. Copyright (C) 2018 by the Institute of
  169. Electrical and Electronics Engineers, Inc and The Open Group.
  170. In the event of any discrepancy between this version and the original IEEE and
  171. The Open Group Standard, the original IEEE and The Open Group Standard
  172. is the referee document. The original Standard can be obtained online at
  173. http://www.opengroup.org/unix/online.html .
  174. .PP
  175. Any typographical or formatting errors that appear
  176. in this page are most likely
  177. to have been introduced during the conversion of the source files to
  178. man page format. To report such errors, see
  179. https://www.kernel.org/doc/man-pages/reporting_bugs.html .