PROLOGThis manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.
NAMEreadonly --- set the readonly attribute for variables
readonly name[=word]... readonly -p
DESCRIPTIONThe variables whose names are specified shall be given the readonly attribute. The values of variables with the readonly attribute cannot be changed by subsequent assignment, nor can those variables be unset by the unset utility. If the name of a variable is followed by =word, then the value of that variable shall be set to word. The readonly special built-in shall support the Base Definitions volume of POSIX.1-2008, Section 12.2, Utility Syntax Guidelines. When -p is specified, readonly writes to the standard output the names and values of all read-only variables, in the following format:
"readonly %s=%s\n", <name>, <value>
"readonly %s\n", <name>
- Variables with values at the time they were output do not have the readonly attribute set.
- Variables that were unset at the time they were output do not have a value at the time at which the saved output is reinput to the shell. When no arguments are given, the results are unspecified.
OPTIONSSee the DESCRIPTION.
OPERANDSSee the DESCRIPTION.
STDOUTSee the DESCRIPTION.
STDERRThe standard error shall be used only for diagnostic messages.
CONSEQUENCES OF ERRORSDefault.
The following sections are informative.
readonly HOME PWD
RATIONALESome historical shells preserve the readonly attribute across separate invocations. This volume of POSIX.1-2008 allows this behavior, but does not require it. The -p option allows portable access to the values that can be saved and then later restored using, for example, a dot script. Also see the RATIONALE for export for a description of the no-argument and -p output cases and a related example. Read-only functions were considered, but they were omitted as not being historical practice or particularly useful. Furthermore, functions must not be read-only across invocations to preclude ``spoofing'' (spoofing is the term for the practice of creating a program that acts like a well-known utility with the intent of subverting the real intent of the user) of administrative or security-relevant (or security-conscious) shell scripts.
SEE ALSOSection 2.14, Special Built-In Utilities The Base Definitions volume of POSIX.1-2008, Section 12.2, Utility Syntax Guidelines
COPYRIGHTPortions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, Copyright (C) 2013 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at www.unix.org/online.html .
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