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.
10
12 readonly — set the readonly attribute for variables
13
15 readonly name[=word]...
16 readonly -p
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20 The variables whose names are specified shall be given the readonly
21 attribute. The values of variables with the readonly attribute cannot
22 be changed by subsequent assignment, nor can those variables be unset
23 by the unset utility. If the name of a variable is followed by =word,
24 then the value of that variable shall be set to word.
25 The readonly special built-in shall support the Base Definitions volume
27 of POSIX.1‐2017, Section 12.2, Utility Syntax Guidelines.
28 When -p is specified, readonly writes to the standard output the names
30 and values of all read-only variables, in the following format:
31 "readonly %s=%s\n", <name>, <value>
34 if name is set, and
36 "readonly %s\n", <name>
39 if name is unset.
41 The shell shall format the output, including the proper use of quoting,
43 so that it is suitable for reinput to the shell as commands that
44 achieve the same value and readonly attribute-setting results in a
45 shell execution environment in which:
46 1. Variables with values at the time they were output do not have the
48 readonly attribute set.
49 2. Variables that were unset at the time they were output do not have
51 a value at the time at which the saved output is reinput to the
52 shell.
53 When no arguments are given, the results are unspecified.
55
57 See the DESCRIPTION.
58
60 See the DESCRIPTION.
61
63 Not used.
64
66 None.
67
69 None.
70
72 Default.
73
75 See the DESCRIPTION.
76
78 The standard error shall be used only for diagnostic messages.
79
81 None.
82
84 None.
85
87 0 All name operands were successfully marked readonly.
88 >0 At least one name could not be marked readonly, or the -p option
90 was specified and an error occurred.
91
93 Default.
94 The following sections are informative.
96
98 None.
99
101 readonly HOME PWD
102
104 Some historical shells preserve the readonly attribute across separate
105 invocations. This volume of POSIX.1‐2017 allows this behavior, but does
106 not require it.
107 The -p option allows portable access to the values that can be saved
109 and then later restored using, for example, a dot script. Also see the
110 RATIONALE for export for a description of the no-argument and -p output
111 cases and a related example.
112 Read-only functions were considered, but they were omitted as not being
114 historical practice or particularly useful. Furthermore, functions must
115 not be read-only across invocations to preclude ``spoofing'' (spoofing
116 is the term for the practice of creating a program that acts like a
117 well-known utility with the intent of subverting the real intent of the
118 user) of administrative or security-relevant (or security-conscious)
119 shell scripts.
120
122 None.
123
125 Section 2.14, Special Built-In Utilities
126 The Base Definitions volume of POSIX.1‐2017, Section 12.2, Utility Syn‐
128 tax Guidelines
129
131 Portions of this text are reprinted and reproduced in electronic form
132 from IEEE Std 1003.1-2017, Standard for Information Technology -- Por‐
133 table Operating System Interface (POSIX), The Open Group Base Specifi‐
134 cations Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of
135 Electrical and Electronics Engineers, Inc and The Open Group. In the
136 event of any discrepancy between this version and the original IEEE and
137 The Open Group Standard, the original IEEE and The Open Group Standard
138 is the referee document. The original Standard can be obtained online
139 at http://www.opengroup.org/unix/online.html .
140 Any typographical or formatting errors that appear in this page are
142 most likely to have been introduced during the conversion of the source
143 files to man page format. To report such errors, see https://www.ker‐
144 nel.org/doc/man-pages/reporting_bugs.html .
145IEEE/The Open Group 2017 READONLY(1P)