1READONLY(1P) POSIX Programmer's Manual READONLY(1P)
2
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 readonly — set the readonly attribute for variables
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16 readonly name[=word]...
17 readonly −p
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21 The variables whose names are specified shall be given the readonly
22 attribute. The values of variables with the readonly attribute cannot
23 be changed by subsequent assignment, nor can those variables be unset
24 by the unset utility. If the name of a variable is followed by =word,
25 then the value of that variable shall be set to word.
26 The readonly special built-in shall support the Base Definitions volume
28 of POSIX.1‐2008, Section 12.2, Utility Syntax Guidelines.
29 When −p is specified, readonly writes to the standard output the names
31 and values of all read-only variables, in the following format:
32 "readonly %s=%s\n", <name>, <value>
34 if name is set, and
36 "readonly %s\n", <name>
38 if name is unset.
40 The shell shall format the output, including the proper use of quoting,
42 so that it is suitable for reinput to the shell as commands that
43 achieve the same value and readonly attribute-setting results in a
44 shell execution environment in which:
45 1. Variables with values at the time they were output do not have the
47 readonly attribute set.
48 2. Variables that were unset at the time they were output do not have
50 a value at the time at which the saved output is reinput to the
51 shell.
52 When no arguments are given, the results are unspecified.
54
56 See the DESCRIPTION.
57
59 See the DESCRIPTION.
60
62 Not used.
63
65 None.
66
68 None.
69
71 Default.
72
74 See the DESCRIPTION.
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77 The standard error shall be used only for diagnostic messages.
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80 None.
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83 None.
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86 Zero.
87
89 Default.
90 The following sections are informative.
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94 None.
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97 readonly HOME PWD
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100 Some historical shells preserve the readonly attribute across separate
101 invocations. This volume of POSIX.1‐2008 allows this behavior, but does
102 not require it.
103 The −p option allows portable access to the values that can be saved
105 and then later restored using, for example, a dot script. Also see the
106 RATIONALE for export for a description of the no-argument and −p output
107 cases and a related example.
108 Read-only functions were considered, but they were omitted as not being
110 historical practice or particularly useful. Furthermore, functions must
111 not be read-only across invocations to preclude ``spoofing'' (spoofing
112 is the term for the practice of creating a program that acts like a
113 well-known utility with the intent of subverting the real intent of the
114 user) of administrative or security-relevant (or security-conscious)
115 shell scripts.
116
118 None.
119
121 Section 2.14, Special Built-In Utilities
122 The Base Definitions volume of POSIX.1‐2008, Section 12.2, Utility Syn‐
124 tax Guidelines
125
127 Portions of this text are reprinted and reproduced in electronic form
128 from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
129 -- Portable Operating System Interface (POSIX), The Open Group Base
130 Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
131 cal and Electronics Engineers, Inc and The Open Group. (This is
132 POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
133 event of any discrepancy between this version and the original IEEE and
134 The Open Group Standard, the original IEEE and The Open Group Standard
135 is the referee document. The original Standard can be obtained online
136 at http://www.unix.org/online.html .
137 Any typographical or formatting errors that appear in this page are
139 most likely to have been introduced during the conversion of the source
140 files to man page format. To report such errors, see https://www.ker‐
141 nel.org/doc/man-pages/reporting_bugs.html .
142IEEE/The Open Group 2013 READONLY(1P)