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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12 readonly - set the readonly attribute for variables
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15 readonly name[=word]...
16 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 IEEE Std 1003.1-2001, 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>
35 if name is set, and
37 "readonly %s\n", <name>
40 if name is unset.
42 The shell shall format the output, including the proper use of quoting,
44 so that it is suitable for reinput to the shell as commands that
45 achieve the same value and readonly attribute-setting results in a
46 shell execution environment in which:
47 1. Variables with values at the time they were output do not have the
49 readonly attribute set.
50 2. Variables that were unset at the time they were output do not have
52 a value at the time at which the saved output is reinput to the
53 shell.
54 When no arguments are given, the results are unspecified.
56
58 See the DESCRIPTION.
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61 See the DESCRIPTION.
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64 Not used.
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67 None.
68
70 None.
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73 Default.
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76 See the DESCRIPTION.
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79 The standard error shall be used only for diagnostic messages.
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82 None.
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85 None.
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88 Zero.
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91 Default.
92 The following sections are informative.
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96 None.
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99 readonly HOME PWD
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102 Some historical shells preserve the readonly attribute across separate
103 invocations. This volume of IEEE Std 1003.1-2001 allows this behavior,
104 but does not require it.
105 The -p option allows portable access to the values that can be saved
107 and then later restored using, for example, a dot script. Also see the
108 RATIONALE for export for a description of the no-argument and -p output
109 cases and a related example.
110 Read-only functions were considered, but they were omitted as not being
112 historical practice or particularly useful. Furthermore, functions must
113 not be read-only across invocations to preclude ``spoofing'' (spoofing
114 is the term for the practice of creating a program that acts like a
115 well-known utility with the intent of subverting the real intent of the
116 user) of administrative or security-relevant (or security-conscious)
117 shell scripts.
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120 None.
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123 Special Built-In Utilities
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126 Portions of this text are reprinted and reproduced in electronic form
127 from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
128 -- Portable Operating System Interface (POSIX), The Open Group Base
129 Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
130 Electrical and Electronics Engineers, Inc and The Open Group. In the
131 event of any discrepancy between this version and the original IEEE and
132 The Open Group Standard, the original IEEE and The Open Group Standard
133 is the referee document. The original Standard can be obtained online
134 at http://www.opengroup.org/unix/online.html .
135IEEE/The Open Group 2003 READONLY(1P)