readonly prevents subsequent changes in the value of any of the name arguments. Parameters of the form
assign value to the KornShell variable name as well as marking name read-only. If readonly is called without arguments it lists, with appropriate quoting, the KornShell variables set as read-only. The following format is used:
This format is suitable for reading by a shell script,
but to ensure the portability of read-only access,
displays read-only variables in the format:
This ensures portability when this output is used as input to a shell.
Normally, this output is captured in a file which is then sourced to reproduce the current environment. Because trying to change a read-only variable fails with an error, you can't successfully source the output unless you go to a new shell.
Possible exit status values:
An attempt to give read-only status to a variable which is already read-only.
Failure due to invalid command line argument.
POSIX.2. x/OPEN Portability Guide 4.0. Windows Server 2012. Windows 8.1. Windows Server 2012 R2. Windows 10. Windows Server 2016. Windows Server 2019. readonly is a built-in command of the Bourne Shell and KornShell on UNIX systems.
The behavior of readonly when called with no arguments is an extension to the POSIX and XPG standards.
This is a special built-in command of the MKS KornShell.
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PTC MKS Toolkit for Professional Developers
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PTC MKS Toolkit 10.3 Documentation Build 39.