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6.10 The Restricted Shell
=========================
If Bash is started with the name `rbash', or the `--restricted' or `-r'
option is supplied at invocation, the shell becomes restricted. A
restricted shell is used to set up an environment more controlled than
the standard shell. A restricted shell behaves identically to `bash'
with the exception that the following are disallowed or not performed:
* Changing directories with the `cd' builtin.
* Setting or unsetting the values of the `SHELL', `PATH', `ENV', or
`BASH_ENV' variables.
* Specifying command names containing slashes.
* Specifying a filename containing a slash as an argument to the `.'
builtin command.
* Specifying a filename containing a slash as an argument to the `-p'
option to the `hash' builtin command.
* Importing function definitions from the shell environment at
startup.
* Parsing the value of `SHELLOPTS' from the shell environment at
startup.
* Redirecting output using the `>', `>|', `<>', `>&', `&>', and `>>'
redirection operators.
* Using the `exec' builtin to replace the shell with another command.
* Adding or deleting builtin commands with the `-f' and `-d' options
to the `enable' builtin.
* Using the `enable' builtin command to enable disabled shell
builtins.
* Specifying the `-p' option to the `command' builtin.
* Turning off restricted mode with `set +r' or `set +o restricted'.
These restrictions are enforced after any startup files are read.
When a command that is found to be a shell script is executed (*note
Shell Scripts::), `rbash' turns off any restrictions in the shell
spawned to execute the script.