READONLY(1POSIX)

✨ PROLOG ✨

okay bestie, before we even get into it — this manual page is part of the POSIX Programmer's Manual. readonly(1POSIX), section 1POSIX, from the POSIX Programmer's Manual, she's a whole legend 💅

But real talk: the Linux implementation of this interface may differ — so go consult the corresponding Linux manual page for the details on Linux behavior. Or, plot twist, the interface might not even be implemented on Linux at all. 🙈

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🎀 NAME 🎀

readonly — set the readonly attribute for variables

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🦋 SYNOPSIS 🦋

readonly name[=word]...

readonly -p

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💖 DESCRIPTION 💖

So basically: the variables whose names you specify get handed the readonly attribute. Once a variable is readonly, its value cannot be changed by any subsequent assignment, and it cannot be unset by the unset utility either. Locked in. No takebacks. 🔒

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.1‐2017, 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>

if name is set, and

"readonly %s\n", <name>

if name is unset.

The shell shall format the output — including the proper use of quoting — so that it's suitable for reinput to the shell as commands that achieve the same value and readonly attribute-setting results in a shell execution environment in which:

1. Variables with values at the time they were output do not have the readonly attribute set.
2. 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. 🫠 Like, nobody's promising anything there.

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🌸 OPTIONS 🌸

See the DESCRIPTION. (that's it, that's the section, she's short and she knows it 🎀)

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🌈 OPERANDS 🌈

See the DESCRIPTION.

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⭐ STDIN ⭐

Not used. She does not read. She does not care. 💅

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🧚 INPUT FILES 🧚

None.

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💜 ENVIRONMENT VARIABLES 💜

None.

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🍓 ASYNCHRONOUS EVENTS 🍓

Default.

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🔥 STDOUT 🔥

See the DESCRIPTION.

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💀 STDERR 💀

The standard error shall be used only for diagnostic messages.

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🦋 OUTPUT FILES 🦋

None.

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✨ EXTENDED DESCRIPTION ✨

None.

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👑 EXIT STATUS 👑

• 0 — All name operands were successfully marked readonly. slay 💖
• >0 — At least one name could not be marked readonly, or the -p option was specified and an error occurred.

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😭 CONSEQUENCES OF ERRORS 😭

Default.

The following sections are informative.

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🌸 APPLICATION USAGE 🌸

None.

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🎀 EXAMPLES 🎀

readonly HOME PWD

that's the whole example, bestie. short king. 👑

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💅 RATIONALE 💅

Some historical shells preserve the readonly attribute across separate invocations. This volume of POSIX.1‐2017 allows this behavior, but does not require it. (so like, optional vibes, no cap)

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'' — and yes, 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. 🚨 not the spoofing, bestie, that's giving villain origin story.

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🦋 FUTURE DIRECTIONS 🦋

None.

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💖 SEE ALSO 💖

• Section 2.14, Special Built-In Utilities
• The Base Definitions volume of POSIX.1‐2017, Section 12.2, Utility Syntax Guidelines

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📜 COPYRIGHT 📜

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. 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 http://www.opengroup.org/unix/online.html .

Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .

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and that's the whole page, bestie 🫶 brought to you by IEEE/The Open Group, dated 2017 — READONLY(1POSIX), periodt. go forth and lock your variables. 💖✨