RESTRICTED SHELL

       If  bash  is  started with the name rbash, or the -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.  It behaves identically
       to bash with the exception that the following are disallowed or not performed:

       ·      changing directories with cd

       ·      setting or unsetting the values of SHELL, PATH, ENV, or BASH_ENV

       ·      specifying command names containing /

       ·      specifying a file name containing a / 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 command to replace the shell with another command

       ·      adding or deleting builtin commands with the -f and -d options to the enable builtin command

       ·      Using the enable builtin command to enable disabled shell builtins

       ·      specifying the -p option to the command builtin command

       ·      turning off restricted mode with set +r or set +o restricted.

       These restrictions are enforced after any startup files are read.

       If  bash  is invoked with the name sh, it tries to mimic the startup behavior of historical versions of sh as closely as possible,
       while conforming to the POSIX standard as well.  When invoked as an interactive login shell, or a non-interactive shell  with  the
       --login  option,  it first attempts to read and execute commands from /etc/profile and ~/.profile, in that order.  The --noprofile
       option may be used to inhibit this behavior.  When invoked as an interactive shell with the name sh, bash looks for  the  variable
       ENV,  expands  its  value  if it is defined, and uses the expanded value as the name of a file to read and execute.  Since a shell
       invoked as sh does not attempt to read and execute commands from any other startup files, the --rcfile option has  no  effect.   A
       non-interactive  shell invoked with the name sh does not attempt to read any other startup files.  When invoked as sh, bash enters
       posix mode after the startup files are read.