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

A shell started with -c option.

bash Startup Files

When bash is invoked as an interactive login shell, or as a non-interactive shell with the --login option, it first executes commands from /etc/profile, if exists.

Them it looks for ~/.bash_profile, ~/.bash_login and ~/.profile in that order. It 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 behavior.

      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.

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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.