- shell built-in function to protect the value of the given variable from reassignment
**readonly [name [= value]]...
The given names are marked readonly and the values of the these names may not be changed by subsequent assignment. If no arguments are given, a list of all readonly names is printed.
The given names are marked readonly and these names cannot be changed by subsequent assignment.
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 formats the output, including the proper use of quoting, so that it is 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:
Variables with values set 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.
On this man page, ksh(1) commands that are preceded by one or two ** (asterisks) are treated specially in the following ways:
Variable assignment lists preceding the command remain in effect when the command completes.
I/O redirections are processed after variable assignments.
Errors cause a script that contains them to abort.
Words, following a command preceded by ** that are in the format of a variable assignment, are expanded with the same rules as a variable assignment. This means that tilde substitution is performed after the = sign and word splitting and file name generation are not performed.
See attributes(5) for descriptions of the following attributes: