linux登陸環(huán)境變量初始化順序
/etc/profile-->/.bash_profile-->/.bash_login-->~/.profile
參考：
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 $- includes i if bash is interactive, allowing a
shell script or a startup file to test this state.
The following paragraphs describe how bash executes its
startup files. If any of the files exist but cannot be
read, bash reports an error. Tildes are expanded in file
names as described below under Tilde Expansion in the
EXPANSION section.
When bash is invoked as an interactive login shell, or as
a non-interactive shell with the --login option, it first
reads and executes commands from the file /etc/profile, if
that file exists. After reading that file, it looks for
~/.bash_profile, ~/.bash_login, and ~/.profile, in that
order, and reads and executes commands from the first one
that exists and is readable. The --noprofile option may
be used when the shell is started to inhibit this behav-
ior.
When a login shell exits, bash reads and executes commands
from the file ~/.bash_logout, if it exists.
When an interactive shell that is not a login shell is
started, bash reads and executes commands from ~/.bashrc,
if that file exists. This may be inhibited by using the
--norc option. The --rcfile file option will force bash
to read and execute commands from file instead of
~/.bashrc.
When bash is started non-interactively, to run a shell
script, for example, it looks for the variable BASH_ENV in
the environment, expands its value if it appears there,
and uses the expanded value as the name of a file to read
and execute. Bash behaves as if the following command
were executed:
if [ -n "$BASH_ENV" ]; then . "$BASH_ENV"; fi
but the value of the PATH variable is not used to search
for the file name.
Part two
用戶登錄到Linux系統(tǒng)后，系統(tǒng)將啟動一個用戶shell。在這個shell中，可以使用shell命令或聲明變量，也可以創(chuàng)建并運行shell腳本程序。運行shell腳本程序時，系統(tǒng)將創(chuàng)建一個子shell。此時，系統(tǒng)中將有兩個shell，一個是登錄時系統(tǒng)啟動的shell，另一個是系統(tǒng)為運行腳本程序創(chuàng)建的shell。當(dāng)一個腳本程序運行完畢，它的腳本shell將終止，可以返回到執(zhí)行該腳本之前的shell。
我們可以在腳本中通過命令export將變量輸出到任何子shell；而通過source命令（.命令），可以執(zhí)行shell腳本，并同時將腳本中的變量輸出到當(dāng)前shell。
Tips
- 有時，我們在crontab上定時調(diào)用在腳本，但是腳本執(zhí)行一些命令沒有成功。這時，我們可以將命令的調(diào)用方式都改成用絕對路徑的方式；還有另一種方法，在腳本里加上如下信息，這樣腳本調(diào)用命令也能正常執(zhí)行了。
export PATH=$PATH:/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin
- 當(dāng)我們更改了環(huán)境變量，需要重新登陸shell才生效。其實也可以通過命令 source 更改的文件 來使其生效。
