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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 $- includes i if bash is interactive, allowing a shell script or a startup file to
test this state.
The following paragraphs describe how bash executes its startup files. If any of the files exist but can_
not be read, bash reports an error. Tildes are expanded in file names as described below under Tilde
Expansion in the EXPANSION section.
When bash is invoked as an interactive login shell, or as a non-interactive shell with the --login option,
it first reads and executes commands from the file /etc/profile, if that file exists. After reading that
file, it looks for ~/.bash_profile, ~/.bash_login, and ~/.profile, in that order, and reads and executes
commands from the first one that exists and is readable. The --noprofile option may be used when the
shell is started to inhibit this behavior.
When a login shell exits, bash reads and executes commands from the file ~/.bash_logout, if it exists.
When an interactive shell that is not a login shell is started, bash reads and executes commands from
~/.bashrc, if that file exists. This may be inhibited by using the --norc option. The --rcfile file
option will force bash to read and execute commands from file instead of ~/.bashrc.
When bash is started non-interactively, to run a shell script, for example, it looks for the variable
BASH_ENV in the environment, expands its value if it appears there, and uses the expanded value as the
name of a file to read and execute. Bash behaves as if the following command were executed:
if [ -n "$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 deter_
mines 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 supplied, no startup files are read, shell functions are not inherited from the environ_
ment, 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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