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INVOCATION
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 output are both
connected to terminals (as determined by isatty(3)), or one
started with the -i option. PS1 is set and $- includes i if bash
is interactive, allowing a shell script or a startup file to test
this state.
The following paragraphs describe how bash executes its startup
files. If any of the files exist but cannot be read, bash reports
an error. Tildes are expanded in file names as described below
under Tilde Expansion in the EXPANSION section.
When bash is invoked as an interactive login shell, or as a non-
interactive shell with the --login option, it first reads and exe_
cutes commands from the file /etc/profile, if that file exists.
After reading that file, it looks for ~/.bash_profile,
~/.bash_login, and ~/.profile, in that order, and reads and exe_
cutes commands from the first one that exists and is readable.
The --noprofile option may be used when the shell is started to
inhibit this behavior.
When a login shell exits, bash reads and executes commands from
the file ~/.bash_logout, if it exists.
When an interactive shell that is not a login shell is started,
bash reads and executes commands from ~/.bashrc, if that file
exists. This may be inhibited by using the --norc option. The
--rcfile file option will force bash to read and execute commands
from file instead of ~/.bashrc.
When bash is started non-interactively, to run a shell script, for
example, it looks for the variable BASH_ENV in the environment,
expands its value if it appears there, and uses the expanded value
as the name of a file to read and execute. Bash behaves as if the
following command were executed:
if [ -n "$BASH_ENV" ]; then . "$BASH_ENV"; fi
but the value of the PATH variable is not used to search for the
file name.
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 ~/.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 sup_
plied, no startup files are read, shell functions are not inher_
ited 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.
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