Bash Invocation

• Invocation Modes
• Invocation Options
• Invocation Environment

A login shell is started either by:

• setting argument 0's first character to - as done by login(1) or exec -l
• providing the -l or --login option

A login shell need not be interactive. A login shell will:

1. Set the Shell Option login_shell in BASHOPTS which may not be unset via the shopt builtin
2. Read & execute commands from profile if it is readable (need not be executable)
3. Read & execute the first user profile found (searched in the order):
   1. .bash_profile
   2. .bash_login
   3. .profile
4. Shell Option --noprofile may be used to suppress this behavior
5. PROCESS COMMANDS
6. exit via:
   • the exit builtin
   • the logout builtin
   • EOF on stdin
7. If the huponexit Shell Option was set in BASHOPTS, then bash sends SIGHUP to all jobs in an interactive shell.
8. Read & execute commands from the readable file .bash_logout

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 filename 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.

When a command that is found to be a shell script is executed (see COMMAND EXECUTION above), rbash turns off any restrictions in the shell spawned to execute the script.

-r If the -r option is present, the shell becomes restricted

               (see RESTRICTED SHELL below).
               
   --restricted
            The shell becomes restricted (see RESTRICTED SHELL below).

enable [-a] [-dnps] [-f filename] [name …] readonly restricted_shell

                    The shell sets this option if it is started in
                    restricted mode (see RESTRICTED SHELL below).  The
                    value may not be changed.  This is not reset when the
                    startup files are executed, allowing the startup files
                    to discover whether or not a shell is restricted.