关于Linux下的环境变量

一、交互式shell和非交互式shell

要搞清bashrc与profile的区别，首先要弄明白什么是交互式shell和非交互式shell，什么是login shell 和non-login shell。

【交互模式】

交互式模式就是shell等待你的输入，并且执行你提交的命令。这种模式被称作交互式是因为shell与用户进行交互。这种模式也是大多数用户非常熟悉的：登录、执行一些命令、签退。当你签退后，shell也终止了。

【非交互模式】

shell也可以运行在另外一种模式：非交互式模式。在这种模式下，shell不与你进行交互，而是读取存放在文件中的命令,并且执行它们。当它读到文件的结尾，shell也就终止了。

bashrc与profile都用于保存用户的环境信息，bashrc用于交互式non-loginshell，而profile用于交互式login shell。

二、几种环境变量配置文件

/etc/profile和/etc/bashrc都是对所有用户生效！

~/.bash_profile和~/.bashrc只对当前用户生效。~表示当前用户的家目录。

/etc/profile中设置的变量（全局）可以作用于任何用户，而~/.bashrc中设置的变量（局部）只能继承/etc/profile中的变量，它们是父子关系。

~/.bash_profile是交互式、login方式进入bash运行的；

~/.bashrc是交互式、non-login方式进入bash运行的；

1. /etc/profile

该文件为系统的每个用户设置环境信息，当用户第一次登录时，该文件被执行。并从/etc/profile.d目录的配置文件中搜集shell的设置。

[root@CentOS6 ~]# more /etc/profile

# /etc/profile

# System wide environment and startup programs, for login setup

# Functions and aliases go in /etc/bashrc

# It's NOT a good idea to change this file unless you know what you

# are doing. It's much better to create a custom.sh shell script in

# /etc/profile.d/ to make custom changes to your environment, as this

# will prevent the need for merging in future updates.

pathmunge () {

    case ":${PATH}:" in

        *:"$1":*)

            ;;

        *)

            if [ "$2" = "after" ] ; then

                PATH=$PATH:$1

            else

                PATH=$1:$PATH

            fi

    esac

}

if [ -x /usr/bin/id ]; then

    if [ -z "$EUID" ]; then

        # ksh workaround

        EUID=`id -u`

        UID=`id -ru`

    fi

    USER="`id -un`"

    LOGNAME=$USER

    MAIL="/var/spool/mail/$USER"

fi

# Path manipulation

if [ "$EUID" = "0" ]; then

    pathmunge /sbin

    pathmunge /usr/sbin

    pathmunge /usr/local/sbin

else

    pathmunge /usr/local/sbin after

    pathmunge /usr/sbin after

    pathmunge /sbin after

fi

HOSTNAME=`/bin/hostname 2>/dev/null`

HISTSIZE=1000

if [ "$HISTCONTROL" = "ignorespace" ] ; then

    export HISTCONTROL=ignoreboth

else

    export HISTCONTROL=ignoredups

fi

export PATH USER LOGNAME MAIL HOSTNAME HISTSIZE HISTCONTROL

# By default, we want umask to get set. This sets it for login shell

# Current threshold for system reserved uid/gids is 200

# You could check uidgid reservation validity in

# /usr/share/doc/setup-*/uidgid file

if [ $UID -gt 199 ] && [ "`id -gn`" = "`id -un`" ]; then

    umask 002

else

    umask 022

fi

for i in /etc/profile.d/*.sh ; do

    if [ -r "$i" ]; then

        if [ "${-#*i}" != "$-" ]; then

            . "$i"

        else

            . "$i" >/dev/null 2>&1

        fi

    fi

done

unset i

unset -f pathmunge

2. /etc/bashrc

为每一个运行bash shell的用户执行此文件。当bash shell被打开时，该文件被读取。

# /etc/bashrc

# System wide functions and aliases

# Environment stuff goes in /etc/profile

# It's NOT a good idea to change this file unless you know what you

# are doing. It's much better to create a custom.sh shell script in

# /etc/profile.d/ to make custom changes to your environment, as this

# will prevent the need for merging in future updates.

# are we an interactive shell?

if [ "$PS1" ]; then

  if [ -z "$PROMPT_COMMAND" ]; then

    case $TERM in

    xterm*)

        if [ -e /etc/sysconfig/bash-prompt-xterm ]; then

            PROMPT_COMMAND=/etc/sysconfig/bash-prompt-xterm

        else

            PROMPT_COMMAND='printf "\033]0;%s@%s:%s\007" "${USER}" "${HOSTNAME%%.*}" "${PWD/#$HOME/~}"'

        fi

        ;;

    screen)

        if [ -e /etc/sysconfig/bash-prompt-screen ]; then

            PROMPT_COMMAND=/etc/sysconfig/bash-prompt-screen

        else

            PROMPT_COMMAND='printf "\033]0;%s@%s:%s\033\\" "${USER}" "${HOSTNAME%%.*}" "${PWD/#$HOME/~}"'

        fi

        ;;

    *)

        [ -e /etc/sysconfig/bash-prompt-default ] && PROMPT_COMMAND=/etc/sysconfig/bash-prompt-default

        ;;

      esac

  fi

  # Turn on checkwinsize

  shopt -s checkwinsize

  [ "$PS1" = "\\s-\\v\\\$ " ] && PS1="[\u@\h \W]\\$ "

  # You might want to have e.g. tty in prompt (e.g. more virtual machines)

  # and console windows

  # If you want to do so, just add e.g.

  # if [ "$PS1" ]; then

  #   PS1="[\u@\h:\l \W]\\$ "

  # fi

  # to your custom modification shell script in /etc/profile.d/ directory

fi

if ! shopt -q login_shell ; then # We're not a login shell

    # Need to redefine pathmunge, it get's undefined at the end of /etc/profile

    pathmunge () {

        case ":${PATH}:" in

            *:"$1":*)

                ;;

            *)

                if [ "$2" = "after" ] ; then

                    PATH=$PATH:$1

                else

                    PATH=$1:$PATH

                fi

        esac

    }

    # By default, we want umask to get set. This sets it for non-login shell.

    # Current threshold for system reserved uid/gids is 200

    # You could check uidgid reservation validity in

    # /usr/share/doc/setup-*/uidgid file

    if [ $UID -gt 199 ] && [ "`id -gn`" = "`id -un`" ]; then

       umask 002

    else

       umask 022

    fi

    # Only display echos from profile.d scripts if we are no login shell

    # and interactive - otherwise just process them to set envvars

    for i in /etc/profile.d/*.sh; do

        if [ -r "$i" ]; then

            if [ "$PS1" ]; then

                . "$i"

            else

                . "$i" >/dev/null 2>&1

            fi

        fi

    done

    unset i

    unset pathmunge

fi

# vim:ts=4:sw=4

3. ~/.bash_profile

每个用户都可使用该文件输入专用于自己使用的shell信息。当用户登录时，该文件仅仅执行一次。默认情况下，他设置一些环境变量，执行用户的

~/.bashrc文件。

[root@CentOS6 ~]# more ~/.bash_profile

# .bash_profile

# Get the aliases and functions

if [ -f ~/.bashrc ]; then

        . ~/.bashrc

fi

# User specific environment and startup programs

PATH=$PATH:$HOME/bin:/usr/local/mysql/bin

export PATH

4.~/.bashrc

该文件包含专用于你的bash shell的bash信息。当登录时及每次打开新的shell时，该文件被读取。

每个用户都有一个~/.bashrc文件，在用户目录下。

[root@CentOS6 ~]# more ~/.bashrc

# .bashrc

# User specific aliases and functions

alias rm='rm -i'

alias cp='cp -i'

alias mv='mv -i'

# Source global definitions

if [ -f /etc/bashrc ]; then

        . /etc/bashrc

fi

5. ~/.bash_logout

当每次退出系统时（退出bash shell），执行该文件。

[root@CentOS6 ~]# more ~/.bash_logout

# ~/.bash_logout

巴特西

关于Linux下的环境变量

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