Bash Concepts

Internal

• bash

Login Shell

A login shell is a shell whose first character of its argument zero is a -, or it was started with the --login option.

Interactive Shell

An interactive shell is a shell started:

• without the -c option
• without non-option arguments
• with the -i option

The interactive shell's standard input and error are both connected to terminals.

$- includes i if the shell is interactive, allowing a script or a startup file to test this state.

Non-interactive Shell

      The  following  paragraphs  describe how bash executes its
      startup files.  If any of the files exist  but  cannot  be
      read,  bash reports an error.  Tildes are expanded in file
      names as described below  under  Tilde  Expansion  in  the
      EXPANSION section.

      When  bash is invoked as an interactive login shell, or as
      a non-interactive shell with the --login option, it  first
      reads and executes commands from the file /etc/profile, if
      that file exists.  After reading that file, it  looks  for
      ~/.bash_profile,  ~/.bash_login,  and  ~/.profile, in that
      order, and reads and executes commands from the first  one
      that  exists  and is readable.  The --noprofile option may
      be used when the shell is started to inhibit  this  behav­
      ior.

      When a login shell exits, bash reads and executes commands
      from the file ~/.bash_logout, if it exists.

      When an interactive shell that is not  a  login  shell  is
      started,  bash reads and executes commands from ~/.bashrc,
      if that file exists.  This may be inhibited by  using  the
      --norc  option.   The --rcfile file option will force bash
      to  read  and  execute  commands  from  file  instead   of
      ~/.bashrc.

      When  bash  is  started  non-interactively, to run a shell
      script, for example, it looks for the variable BASH_ENV in
      the  environment,  expands  its value if it appears there,
      and uses the expanded value as the name of a file to  read
      and  execute.   Bash  behaves  as if the following command
      were executed:
             if [ -n "$BASH_ENV" ]; then . "$BASH_ENV"; fi
      but the value of the PATH variable is not used  to  search
      for the file name.