Here's the info from man bash on my debian system:
A login shell is one whose first character of argument zero is a -, or one started with the --login option.
An interactive shell is one started without non-option arguments and without the -c option whose standard
input and error are both connected to terminals (as determined by isatty(3)), or one started with the -i
option. PS1 is set and $- includes i if bash is interactive, allowing a shell script or a startup file to
test this state.
The following paragraphs describe how bash executes its startup files. If any of the files exist but cannot
be read, bash reports an error. Tildes are expanded in file names as described below under Tilde Expansion in
the EXPANSION section.
When bash is invoked as an interactive login shell, or as a non-interactive shell with the --login option, it
first reads and executes commands from the file /etc/profile, if that file exists. After reading that file,
it looks for ~/.bash_profile, ~/.bash_login, and ~/.profile, in that order, and reads and executes commands
from the first one that exists and is readable. The --noprofile option may be used when the shell is started
to inhibit this behavior.
When a login shell exits, bash reads and executes commands from the file ~/.bash_logout, if it exists.
When an interactive shell that is not a login shell is started, bash reads and executes commands from
/etc/bash.bashrc and ~/.bashrc, if these files exist. This may be inhibited by using the --norc option. The
--rcfile file option will force bash to read and execute commands from file instead of /etc/bash.bashrc and
~/.bashrc.
When bash is started non-interactively, to run a shell script, for example, it looks for the variable BASH_ENV
in the environment, expands its value if it appears there, and uses the expanded value as the name of a file
to read and execute. Bash behaves as if the following command were executed:
if [ -n "$BASH_ENV" ]; then . "$BASH_ENV"; fi
but the value of the PATH variable is not used to search for the file name.
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.
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, interactive 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 by the remote shell daemon, usually rshd. If bash determines
it is being run by rshd, it reads and executes commands from /etc/bash.bashrc and ~/.bashrc, if these files
exist and are 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 variable, if it appears in the environment, is 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.
So, I think I had it backwards. I'm guessing you are using terminal. When you are starting up terminal it must be initiating bash as an interactive login shell.
).