holy shit bash!

hsb.txt

       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
       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 inhib‐
       ited 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  vari‐
       able 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.

       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  ~/.pro‐
       file, 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.

       When bash is started in posix  mode,  as  with  the
       --posix  command  line option, it follows the POSIX
       standard for startup files.  In this mode, interac‐
       tive  shells  expand  the ENV variable and commands
       are read and executed from the file whose  name  is
       the  expanded  value.   No  other startup files are
       read.

       Bash attempts to determine when  it  is  being  run
       with its standard input connected to a network con‐
       nection, as when executed by the remote shell  dae‐
       mon, usually rshd, or the secure shell daemon sshd.
       If bash determines it is being run in this fashion,
       it  reads  and executes commands from ~/.bashrc, if
       that file exists and is readable.  It will  not  do
       this  if  invoked  as sh.  The --norc option may be
       used to inhibit this  behavior,  and  the  --rcfile
       option  may  be  used  to  force another file to be
       read, but rshd does not generally invoke the  shell
       with those options or allow them to be specified.

       If  the  shell  is  started with the effective user
       (group) id not equal to the real user  (group)  id,
       and the -p option is not supplied, no startup files
       are read, shell functions are  not  inherited  from
       the  environment,  the SHELLOPTS, BASHOPTS, CDPATH,
       and GLOBIGNORE variables, if  they  appear  in  the
       environment, are ignored, and the effective user id
       is set to the real user id.  If the  -p  option  is
       supplied at invocation, the startup behavior is the
       same, but the effective user id is not reset.