摘自IBM官方网站，原文地址：
The /etc/environment, /etc/profile, and .profile files are run once at
login time. The .env file, on the other hand, is run every time you open
a new shell or a window.
* /etc/environment file
The first file that the operating system uses at login time is the
/etc/environment file. The /etc/environment file contains variables
specifying the basic environment for all processes.
* /etc/profile file
The second file that the operating system uses at login time is the /etc/profile file.
* .profile file
The .profile file is present in your home ($HOME) directory and lets you customize your individual working environment.
* .env file
A fourth file that the operating system uses at login time is the
.env file, if your .profile contains the following line: export
ENV=$HOME/.env
/etc/environment file
The first file that the operating system uses at login time is the
/etc/environment file. The /etc/environment file contains variables
specifying the basic environment for all processes.
When a new process begins, the exec subroutine makes an array of strings
available that have the form Name=Value. This array of strings is
called the environment. Each name defined by one of the strings is
called an environment variable or shell variable. The exec subroutine
allows the entire environment to be set at one time.
When you log in, the system sets environment variables from the
/etc/environment file before reading your login profile, named .profile.
The following variables make up the basic environment:
HOME The full path name of the user's login or HOME directory.
The login program sets this to the name specified in the /etc/passwd
file.
LANG The locale name currently in effect. The LANG variable is
initially set in the /etc/profile file at installation time.
NLSPATH The full path name for message catalogs.
LOCPATH The full path name of the location of National Language Support tables.
PATH The sequence of directories that commands, such as sh,
time, nice and nohup, search when looking for a command whose path name
is incomplete.
TZ The time zone information. The TZ environment variable is
initially set by the /etc/profile file, the system login profile.
/etc/profile file
The second file that the operating system uses at login time is the /etc/profile file.
The /etc/profile file controls system-wide default variables, such as:
* Export variables
* File creation mask (umask)
* Terminal types
* Mail messages to indicate when new mail has arrived
The system administrator configures the /etc/profile file for all users
on the system. Only the system administrator can change this file.
The following example is a typical /etc/profile file:
#Set file creation mask
unmask 022
#Tell me when new mail arrives
MAIL=/usr/mail/$LOGNAME
#Add my /bin directory to the shell search sequence
PATH=/usr/bin:/usr/sbin:/etc::
#Set terminal type
TERM=lft
#Make some environment variables global
export MAIL PATH TERM
For detailed information about the /etc/profile file, see the AIX 5L™ Version 5.3 Files Reference .
.profile file
The .profile file is present in your home ($HOME) directory and lets you customize your individual working environment.
Because the .profile file is hidden, use the ls -a command to list it.
After the login program adds the LOGNAME (login name) and HOME (login
directory) variables to the environment, the commands in the
$HOME/.profile file are executed if the file is present. The .profile
file contains your individual profile that overrides the variables set
in the /etc/profile file. The .profile file is often used to set
exported environment variables and terminal modes. You can customize
your environment by modifying the .profile file. Use the .profile file
to control the following defaults:
* Shells to open
* Prompt appearance
* Keyboard sound
The following example is a typical .profile file:
PATH=/usr/bin:/etc:/home/bin1:/usr/lpp/tps4.0/user::
epath=/home/gsc/e3:
export PATH epath
csh
This example has defined two path variables (PATH and epath), exported them, and opened a C shell (csh).
.env file
A fourth file that the operating system uses at login time is the .env
file, if your .profile contains the following line: export
ENV=$HOME/.env
The .env file lets you customize your individual working environment
variables. Because the .env file is hidden, use the ls -a command to
list it. For more information about the ls command, see ls. The .env
file contains the individual user environment variables that override
the variables set in the /etc/environment file. You can customize your
environment variables as desired by modifying your .env file.
The following example is a typical .env file:
export myid=`id | sed -n -e 's/).*$//' -e 's/^.*(//p'`
#set prompt: login & system name & path
if [ $myid = root ]
then typeset -x PSCH='#:\${PWD}> '
PS1="#:\${PWD}> "
else typeset -x PSCH='>'
PS1="$LOGNAME@$UNAME:\${PWD}> "
PS2=">"
PS3="#?"
fi
export PS1 PS2 PS3
#setup my command aliases
alias ls="/bin/ls -CF" \
d="/bin/ls -Fal | pg" \
rm="/bin/rm -i" \
up="cd .."
Note: When modifying the .env file, ensure that newly created
environment variables do not conflict with standard variables such as
MAIL, PS1, PS2, and IFS.
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