1UNSET(1P) POSIX Programmer's Manual UNSET(1P)
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6 This manual page is part of the POSIX Programmer's Manual. The Linux
7 implementation of this interface may differ (consult the corresponding
8 Linux manual page for details of Linux behavior), or the interface may
9 not be implemented on Linux.
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13 unset — unset values and attributes of variables and functions
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16 unset [−fv] name...
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19 Each variable or function specified by name shall be unset.
20 If −v is specified, name refers to a variable name and the shell shall
22 unset it and remove it from the environment. Read-only variables cannot
23 be unset.
24 If −f is specified, name refers to a function and the shell shall unset
26 the function definition.
27 If neither −f nor −v is specified, name refers to a variable; if a
29 variable by that name does not exist, it is unspecified whether a func‐
30 tion by that name, if any, shall be unset.
31 Unsetting a variable or function that was not previously set shall not
33 be considered an error and does not cause the shell to abort.
34 The unset special built-in shall support the Base Definitions volume of
36 POSIX.1‐2008, Section 12.2, Utility Syntax Guidelines.
37 Note that:
39 VARIABLE=
41 is not equivalent to an unset of VARIABLE; in the example, VARIABLE is
43 set to "". Also, the variables that can be unset should not be misin‐
44 terpreted to include the special parameters (see Section 2.5.2, Special
45 Parameters).
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48 See the DESCRIPTION.
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51 See the DESCRIPTION.
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54 Not used.
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57 None.
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60 None.
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63 Default.
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66 Not used.
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69 The standard error shall be used only for diagnostic messages.
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72 None.
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75 None.
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78 0 All name operands were successfully unset.
79 >0 At least one name could not be unset.
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83 Default.
84 The following sections are informative.
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88 None.
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91 Unset VISUAL variable:
92 unset −v VISUAL
94 Unset the functions foo and bar:
96 unset −f foo bar
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100 Consideration was given to omitting the −f option in favor of an
101 unfunction utility, but the standard developers decided to retain his‐
102 torical practice.
103 The −v option was introduced because System V historically used one
105 name space for both variables and functions. When unset is used without
106 options, System V historically unset either a function or a variable,
107 and there was no confusion about which one was intended. A portable
108 POSIX application can use unset without an option to unset a variable,
109 but not a function; the −f option must be used.
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112 None.
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115 Section 2.14, Special Built-In Utilities
116 The Base Definitions volume of POSIX.1‐2008, Section 12.2, Utility Syn‐
118 tax Guidelines
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121 Portions of this text are reprinted and reproduced in electronic form
122 from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
123 -- Portable Operating System Interface (POSIX), The Open Group Base
124 Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
125 cal and Electronics Engineers, Inc and The Open Group. (This is
126 POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
127 event of any discrepancy between this version and the original IEEE and
128 The Open Group Standard, the original IEEE and The Open Group Standard
129 is the referee document. The original Standard can be obtained online
130 at http://www.unix.org/online.html .
131 Any typographical or formatting errors that appear in this page are
133 most likely to have been introduced during the conversion of the source
134 files to man page format. To report such errors, see https://www.ker‐
135 nel.org/doc/man-pages/reporting_bugs.html .
136IEEE/The Open Group 2013 UNSET(1P)