Linux环境变量：查、改、删

最新推荐文章于 2025-11-07 09:47:22 发布

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#环境变量 #Path #bashrc

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本文介绍了Linux环境变量，包括其定义、查看方法、如何创建和删除用户自定义变量、临时与永久修改PATH以及环境变量持久化的方法。重点讨论了环境文件如/etc/profile和用户启动文件的作用。

Linux环境变量需要知道的内容：

什么是环境变量；
创建自己的环境变量；
删除环境变量；
默认shell环境变量；
设置PATH环境变量；
定位环境文件；

环境变量

Environment variable，定义系统会话和环境信息的变量或者参数。可以快速访问和修改内存中的数据。
系统的环境变量都用大写，以区分普通用户的环境变量。

全局变量
全局变量对shell会话和所有子shell会话都有效。局部变量只对生成他们的shell会话有效。
查看命令：env 或printenv
查看某个环境变量：printenv “变量名”，或者 echo $变量名

提示：变量名前加$，可以将变量用于命令行中，比如需要引用环境变量时，需要加$符号.

shaphicprb13137:~ # env
LESSKEY=/etc/lesskey.bin
MALLOC_MMAP_MAX_=65536
MANPATH=/usr/share/man:/usr/local/man:/usr/local/share/man
NNTPSERVER=news
XDG_SESSION_ID=844641
HOSTNAME=shaphicprb13137
XKEYSYMDB=/usr/X11R6/lib/X11/XKeysymDB
SHELL=/bin/bash		//bash shell的全路径名
TERM=xterm
HOST=shaphicprb13137		//当前主机名称
HISTSIZE=0		//history命令可以显示的命令行数
PROFILEREAD=true
SSH_CLIENT=10.164.148.237 58175 22	//ssh的客户端地址和端口
MORE=-sl
SSH_TTY=/dev/pts/0		//SSH默认使用的tty设备
MALLOC_TRIM_THRESHOLD_=131072
LC_ALL=en_US.UTF-8
USER=root
LS_COLORS=no=00:fi=00:di=01;34:ln=00;36:pi=40;33:so=01;35:do=01;35:bd=40;33;01:cd=40;33;01:or=41;33;01:ex=00;32:*.cmd=00;32:*.exe=01;32:*.com=01;32:*.bat=01;32:*.btm=01;32:*.dll=01;32:*.tar=00;31:*.tbz=00;31:*.tgz=00;31:*.rpm=00;31:*.deb=00;31:*.arj=00;31:*.taz=00;31:*.lzh=00;31:*.lzma=00;31:*.zip=00;31:*.zoo=00;31:*.z=00;31:*.Z=00;31:*.gz=00;31:*.bz2=00;31:*.tb2=00;31:*.tz2=00;31:*.tbz2=00;31:*.xz=00;31:*.avi=01;35:*.bmp=01;35:*.fli=01;35:*.gif=01;35:*.jpg=01;35:*.jpeg=01;35:*.mng=01;35:*.mov=01;35:*.mpg=01;35:*.pcx=01;35:*.pbm=01;35:*.pgm=01;35:*.png=01;35:*.ppm=01;35:*.tga=01;35:*.tif=01;35:*.xbm=01;35:*.xpm=01;35:*.dl=01;35:*.gl=01;35:*.wmv=01;35:*.aiff=00;32:*.au=00;32:*.mid=00;32:*.mp3=00;32:*.ogg=00;32:*.voc=00;32:*.wav=00;32:
XNLSPATH=/usr/share/X11/nls
MALLOC_TOP_PAD_=131072
HOSTTYPE=x86_64		//主机类型
QEMU_AUDIO_DRV=pa
MALLOC_ARENA_MAX=2
FROM_HEADER=
PAGER=less
CSHEDIT=emacs
XDG_CONFIG_DIRS=/etc/xdg
MINICOM=-c on
LIBGL_DEBUG=quiet
PATH=/sbin:/usr/sbin:/usr/local/sbin:/root/bin:/usr/local/bin:/usr/bin:/bin:/usr/bin/X11:/usr/games		//冒号分割的目录列表，作为cd命令的搜索路径
MAIL=/var/mail/root		//当前用户收件箱的文件名
CPU=x86_64
PWD=/root
INPUTRC=/etc/inputrc
LANG=en_US
PYTHONSTARTUP=/etc/pythonstart
AUDIODRIVER=pulseaudio
GPG_TTY=/dev/pts/0
HOME=/root		//当前主目录
SHLVL=4			//shell的层级
QT_SYSTEM_DIR=/usr/share/desktop-data
OSTYPE=linux
LESS_ADVANCED_PREPROCESSOR=no
SDL_AUDIODRIVER=pulse
ALSA_CONFIG_PATH=/etc/alsa-pulse.conf
LS_OPTIONS=-A -N --color=tty -T 0
WINDOWMANAGER=env GNOME_SHELL_SESSION_MODE=classic SLE_CLASSIC_MODE=1 gnome-session --session gnome-classic
LOGNAME=root
MACHTYPE=x86_64-suse-linux
LESS=-M -I -R
G_FILENAME_ENCODING=@locale,UTF-8,ISO-8859-15,CP1252
CVS_RSH=ssh
SSH_CONNECTION=10.164.148.237 58175 100.107.250.59 22
XDG_DATA_DIRS=/usr/share
LESSOPEN=lessopen.sh %s
DISPLAY=localhost:10.0
XDG_RUNTIME_DIR=/run/user/0
XAUTHLOCALHOSTNAME=shaphicprb13137
LESSCLOSE=lessclose.sh %s %s
MALLOC_MMAP_THRESHOLD_=131072
G_BROKEN_FILENAMES=1
COLORTERM=1
_=/usr/bin/env
OLDPWD=/root/.ssh
You have new mail in /var/mail/root
shaphicprb13137:~ # printenv HOME
/root
shaphicprb13137:~ # echo $HOME
/root
shaphicprb13137:~ # ls $HOME
.bash_history  .dbus      ftp-0.17-66.x86_64.rpm                 .local                         pkcs11-helper-1.11-5.3.x86_64.rpm  Templates  .viminfo      .Xauthority
.bash_profile  Desktop    .gnupg                                 Music                          PreInstall                         test2      .xauth83zp1l  .xauthPhGsb8
bin            Documents  .ICEauthority                          .mysql_history                 PreInstall_NCE.zip                 text2.txt  .xauthGLFA5f  .xsession-errors-:0
.cache         Downloads  inst-sys                               openvpn-2.3.8-12.1.x86_64.rpm  Public                             Videos     .xauthjekM76
.config        .esd_auth  libpkcs11-helper1-1.11-5.3.x86_64.rpm  Pictures                       .ssh                               .vim       .xauthN4KDjI

局部变量
全局变量对shell会话和所有子shell会话都有效。局部变量只对生成他们的shell会话有效。
Linux中查看局部变量有些复杂，并没有一个专有局部变量查看命令。可以通过set命令显示某个特定进程设置的所有环境变量，包括局部变量、全局变量以及用户自定义变量。

shaphicprb13137:~ # set
ALSA_CONFIG_PATH=/etc/alsa-pulse.conf
AUDIODRIVER=pulseaudio
BASH=/bin/bash
BASHOPTS=checkwinsize:cmdhist:complete_fullquote:expand_aliases:extglob:extquote:force_fignore:histappend:interactive_comments:progcomp:promptvars:sourcepath
BASH_ALIASES=()
BASH_ARGC=()
BASH_ARGV=()
BASH_CMDS=()
……
quote ()
{
    local quoted=${1//\'/\'\\\'\'};
    printf "'%s'" "$quoted"
}
quote_readline ()
{
    local quoted;
    _quote_readline_by_ref "$1" ret;
    printf %s "$ret"
}
remount ()
{
    /bin/mount -o remount,${1+"$@"}
}
spwd ()
{
    ( IFS=/;
    set $PWD;
    if test $# -le 3; then
        echo "$PWD";
    else
        eval echo \"..\${$(($#-1))}/\${$#}\";
    fi )
}
startx ()
{
    test -x /usr/bin/startx || {
        echo "No startx installed" 1>&2;
        return 1
    };
    /usr/bin/startx ${1+"$@"} 2>&1 | tee $HOME/.xsession-errors
}

用户自定义变量

设置局部用户自定义变量：赋值
只需要用=赋值即可，局部的变量只对本shell进程内有效。赋值有空格和符号时，要加双引号。不可以有空格！！
定义局部自定义变量的意义是，在本shell内可以随时调用该变量。

shaphicprb13137:~ # myvar=HelloLinux
You have new mail in /var/mail/root
shaphicprb13137:~ # echo $myvar
HelloLinux
shaphicprb13137:~ # myvar2="Hello Linux!"
shaphicprb13137:~ # echo $myvar2
Hello Linux!
shaphicprb13137:~ #

注意这样定义的变量只在本shell内有效，其他子shell或者父shell内无效。如下：

shaphicprb13137:~ # bash
shaphicprb13137:~ # ps --forest
   PID TTY          TIME CMD
165785 pts/0    00:00:00 bash
191218 pts/0    00:00:00  \_ bash
193182 pts/0    00:00:00      \_ bash
194820 pts/0    00:00:00          \_ bash
153722 pts/0    00:00:00              \_ bash
160557 pts/0    00:00:00                  \_ ps
shaphicprb13137:~ # echo $myvar

shaphicprb13137:~ # echo $myvar2

shaphicprb13137:~ #

设置全局环境变量：export
步骤：先创建一个环境变量，然后export导出到全局变量。导出时，直接导出变量名，不需要加$
使用$的诀窍：使用变量时，需要加$；操作变量时，不需要加$。

shaphicprb13137:~ # ps --forest
   PID TTY          TIME CMD
165785 pts/0    00:00:00 bash
191218 pts/0    00:00:00  \_ bash
193182 pts/0    00:00:00      \_ bash
194820 pts/0    00:00:00          \_ bash
193059 pts/0    00:00:00              \_ bash
196424 pts/0    00:00:00                  \_ ps
shaphicprb13137:~ # echo $myvar

shaphicprb13137:~ # exit
exit
You have new mail in /var/mail/root
shaphicprb13137:~ # echo $myvar
HelloLinux
shaphicprb13137:~ # echo $myvar2
Hello Linux!
shaphicprb13137:~ # export myvar
shaphicprb13137:~ # export myvar2
shaphicprb13137:~ # bash
shaphicprb13137:~ # ps --forest
   PID TTY          TIME CMD
165785 pts/0    00:00:00 bash
191218 pts/0    00:00:00  \_ bash
193182 pts/0    00:00:00      \_ bash
194820 pts/0    00:00:00          \_ bash
228562 pts/0    00:00:00              \_ bash
233863 pts/0    00:00:00                  \_ ps
shaphicprb13137:~ # echo $myvar
HelloLinux
shaphicprb13137:~ # echo $myvar2
Hello Linux!
shaphicprb13137:~ #

删除环境变量：unset
上述步骤中设置的变量可以通过unset “变量名”的方式删除。

shaphicprb13137:~ #
shaphicprb13137:~ # echo $myvar
HelloLinux
shaphicprb13137:~ # echo $myvar2
Hello Linux!
shaphicprb13137:~ # unset myvar
shaphicprb13137:~ # unset myvar2
shaphicprb13137:~ # ps --forest
   PID TTY          TIME CMD
165785 pts/0    00:00:00 bash
191218 pts/0    00:00:00  \_ bash
193182 pts/0    00:00:00      \_ bash
194820 pts/0    00:00:00          \_ bash
228562 pts/0    00:00:00              \_ bash
 63321 pts/0    00:00:00                  \_ ps
shaphicprb13137:~ # exit
exit
You have new mail in /var/mail/root
shaphicprb13137:~ # exit
exit
You have new mail in /var/mail/root
shaphicprb13137:~ # echo $myvar

shaphicprb13137:~ # echo $myvar2

shaphicprb13137:~ # ps --forest
   PID TTY          TIME CMD
165785 pts/0    00:00:00 bash
191218 pts/0    00:00:00  \_ bash
193182 pts/0    00:00:00      \_ bash
 85964 pts/0    00:00:00          \_ ps
shaphicprb13137:~ #

注意：在子进程中删除的全局变量，只对子进程生效，父进程不变。

修改path环境变量：临时修改

方法一：添加指定目录到PATH
PATH=$PATH:“目录”

方法二：添加当前目录到PATH
PATH=$PATH:.
两种方法都是临时修改，退出系统或者重启系统后则会丢失.

shaphicprb13137:~ # echo $PATH
/sbin:/usr/sbin:/usr/local/sbin:/root/bin:/usr/local/bin:/usr/bin:/bin:/usr/bin/X11:/usr/games
You have new mail in /var/mail/root
shaphicprb13137:~ # PATH=$PATH:/etc
shaphicprb13137:~ # echo $PATH
/sbin:/usr/sbin:/usr/local/sbin:/root/bin:/usr/local/bin:/usr/bin:/bin:/usr/bin/X11:/usr/games:/etc

shaphicprb13137:/etc # PATH=$PATH:.
shaphicprb13137:/etc # echo $PATH
/sbin:/usr/sbin:/usr/local/sbin:/root/bin:/usr/local/bin:/usr/bin:/bin:/usr/bin/X11:/usr/games:/etc:.
shaphicprb13137:/etc #

环境变量持久化：永久性修改环境变量

Linux在启动时，会默认在几个文件中查找命令，这些文件就是启动文件或者环境文件。我们将环境变量写入启动文件中，每次登陆或者启动系统，都会执行文件中的变量，就实现了环境变量的持久化。

Shell的启动文件有5个，分别是一个系统启动文件/etc/profile，4个用户启动文件$HOME/下的4个文件，这四个文件是可以根据用户需求自己定制的。
- /etc/profile
- $HOME/.bash_profile
- $HOME/.bashrc
- $HOME/.bash_login
- $HOME/.profile

Linux推荐通过修改用户启动文件来实现环境变量持久化。或者在/etc/profile.d目录中创建一个.sh结尾的文件，把所有新的或修改过得和全局环境变量放在文件中。

系统启动文件/etc/profile
/etc/profile是bash shell默认的主启动文件，只要启动就会执行其中的命令。其中会调度其他目录下的一下命令文件。
例如：

shaphicprb13137:/etc # cat /etc/profile
# /etc/profile for SUSE Linux
#
# PLEASE DO NOT CHANGE /etc/profile. There are chances that your changes
# will be lost during system upgrades. Instead use /etc/profile.local for
# your local settings, favourite global aliases, VISUAL and EDITOR
# variables, etc ...

#
# Check which shell is reading this file
#
if test -f /proc/mounts ; then
  if ! is=$(readlink /proc/$$/exe 2>/dev/null) ; then
    case "$0" in
    *pcksh)     is=ksh  ;;
    *)          is=sh   ;;
    esac
  fi
  case "$is" in
    */bash)     is=bash
        case "$0" in
        sh|-sh|*/sh)
                is=sh   ;;
        esac            ;;
    */ash)      is=ash  ;;
    */dash)     is=ash  ;;
    */ksh)      is=ksh  ;;
    */ksh93)    is=ksh  ;;
    */pdksh)    is=ksh  ;;
    */mksh)     is=ksh  ;;
    */lksh)     is=ksh  ;;
    */*pcksh)   is=ksh  ;;
    */zsh)      is=zsh  ;;
    */*)        is=sh   ;;
  esac
  #
  # `r' in $- occurs *after* system files are parsed
  #
  for a in $SHELL ; do
    case "$a" in
      */r*sh)
        readonly restricted=true ;;
      -r*|-[!-]r*|-[!-][!-]r*)
        readonly restricted=true ;;
      --restricted)
        readonly restricted=true ;;
    esac
  done
  unset a
else
  is=sh
fi

#
# Call common progams from /bin or /usr/bin only
#
path ()
{
    command -p ${1+"$@"}
}

#
# Initialize terminal
#
tty=`path tty 2> /dev/null`
test $? -ne 0 && tty=""
if test -O "$tty" -a -n "$PS1"; then
    test -z "${TERM}"           && { TERM=linux; export TERM; }
    test "${TERM}" = "unknown"  && { TERM=linux; export TERM; }
    test "${TERM}" = "ibm327x"  && { TERM=dumb;  export TERM; }
    # Do not change settings on local line if connected to remote
    if test -z "$SSH_TTY" -a "${TERM}" != "dumb" ; then
        path stty sane cr0 pass8 dec
        path tset -I -Q
    fi
    # on iSeries virtual console, detect screen size and terminal
    if test -d /proc/iSeries -a \( "$tty" = "/dev/tty1" -o "$tty" = "/dev/console" \) ; then
        LINES=24
        COLUMNS=80
        export LINES COLUMNS TERM
        eval `path initviocons -q -e`
    fi
fi
unset TERMCAP

#
# Time until a complete key sequence must have arrived
#
#ESCDELAY=2000
#export ESCDELAY

#
# The user file-creation mask
#
# The global umask value is stored in /etc/login.defs and
# will be set by pam_umask.so (see "man pam_umask").
#umask 022

#
# Setup for gzip and (t)csh users
#
if test -z "$PROFILEREAD" ; then
    # GZIP=-9
    # export GZIP
    CSHEDIT=emacs
    export CSHEDIT
fi

#
# ksh/ash sometimes do not know
#
test -z "$UID"  && readonly  UID=`path id -ur 2> /dev/null`
test -z "$EUID" && readonly EUID=`path id -u  2> /dev/null`
test -z "$USER" && USER=`path id -un 2> /dev/null`
test -z "$MAIL" && MAIL=/var/spool/mail/$USER
if test -x /bin/uname ; then
    test -z "$HOST" && HOST=`/bin/uname -n`
    test "$HOST" = "localhost" && HOST=`/bin/uname -n`
    test -z "$CPU"  &&  CPU=`/bin/uname -m`
fi
# Remark: /proc/sys/kernel/domainname and the program domainname
# its self will provide the NIS/YP domainname, see domainname(8).
if test -s /etc/HOSTNAME ; then
    test -z "$HOSTNAME" && HOSTNAME=`cat /etc/HOSTNAME`
else
    test -z "$HOSTNAME" && HOSTNAME=$HOST
fi
test -z "$LOGNAME"  && LOGNAME=$USER
case "$CPU" in
    i?86) HOSTTYPE=i386   ;;
    *)    HOSTTYPE=${CPU} ;;
esac
  OSTYPE=linux
MACHTYPE=${CPU}-suse-${OSTYPE}
# Do NOT export UID, EUID, USER, and LOGNAME
export MAIL HOST CPU HOSTNAME HOSTTYPE OSTYPE MACHTYPE

#
# You may use /etc/initscript, /etc/profile.local or the
# ulimit package instead to set up ulimits and your PATH.
#
# if test "$is" != "ash" -a ! -r /etc/initscript; then
#     ulimit -Sc 0              # don't create core files
#     ulimit -Sd $(ulimit -Hd)
#     ulimit -Ss $(ulimit -Hs)
#     ulimit -Sm $(ulimit -Hm)
# fi

#
# Make path more comfortable
#
if test -z "$PROFILEREAD" ; then
    PATH=/usr/local/bin:/usr/bin:/bin
    if test "$HOME" != "/" ; then
        for dir in $HOME/bin/$CPU $HOME/bin ; do
            test -d $dir && PATH=$dir:$PATH
        done
    fi
    if test "$UID" = 0 ; then
        test -d /opt/kde3/sbin  && PATH=/opt/kde3/sbin:$PATH
        PATH=/sbin:/usr/sbin:/usr/local/sbin:$PATH
    fi
    for dir in  /usr/X11/bin \
                /usr/bin/X11 \
                /usr/X11R6/bin \
                /var/lib/dosemu \
                /usr/games \
                /opt/bin \
                /opt/kde3/bin \
                /opt/kde2/bin \
                /opt/kde/bin \
                /usr/openwin/bin \
                /opt/cross/bin
    do
        test -d $dir && PATH=$PATH:$dir
    done
    unset dir
    export PATH
fi

#
# Many programs using readline library for line editing
# should know about this (e.g. bash)
#
if test -z "$INPUTRC" ; then
    INPUTRC=/etc/inputrc
    test -s $HOME/.inputrc && INPUTRC=$HOME/.inputrc
    export INPUTRC
fi

#
# Most bourn shell clones knows about this
#
if test -z "$PROFILEREAD" ; then
    HISTSIZE=1000
    export HISTSIZE
fi

#
# Set some environment variables for TeX/LaTeX (Not used due luatex)
#
#if test -n "$TEXINPUTS" ; then
#    TEXINPUTS=":$TEXINPUTS:$HOME/.TeX:/usr/share/doc/.TeX:/usr/doc/.TeX"
#else
#    TEXINPUTS=":$HOME/.TeX:/usr/share/doc/.TeX:/usr/doc/.TeX"
#fi
#export TEXINPUTS

#
# Configure the default pager on SuSE Linux
#
if test -z "$LESS" -a -x /usr/bin/less ; then
    LESS="-M -I -R"
    LESSOPEN="lessopen.sh %s"
    LESSCLOSE="lessclose.sh %s %s"
    LESS_ADVANCED_PREPROCESSOR="no"
    if test -s /etc/lesskey.bin ; then
        LESSKEY=/etc/lesskey.bin
    fi
    PAGER=less
    MORE=-sl
    export LESSOPEN LESSCLOSE LESS LESSKEY PAGER LESS_ADVANCED_PREPROCESSOR MORE
fi

#
# Minicom
#
if test -z "$PROFILEREAD" ; then
    MINICOM="-c on"
    export MINICOM
fi

#
# Current manpath
#
if test -z "$PROFILEREAD" ; then
    tmp="$MANPATH"
    unset MANPATH
    if test -n "$tmp" ; then
        MANPATH="${tmp}:`test -x /usr/bin/manpath && /usr/bin/manpath -q`"
    else
        MANPATH="`test -x /usr/bin/manpath && /usr/bin/manpath -q`"
    fi
    unset tmp
    export MANPATH
fi

#
# Some applications do not handle the XAPPLRESDIR environment properly,
# when it contains more than one directory. More than one directory only
# makes sense if you have a client with /usr mounted via nfs and you want
# to configure applications machine dependent. Uncomment the lines below
# if you want this.
#
#XAPPLRESDIR="$XAPPLRESDIR:/var/X11R6/app-defaults:/usr/X11R6/lib/X11/app-defaults"
#export XAPPLRESDIR

#
# These settings are recommended for old motif applications
#
if test -z "$PROFILEREAD" ; then
    if [ -r /usr/share/X11/XKeysymDB ]; then
        export XKEYSYMDB=/usr/share/X11/XKeysymDB
    else
        export XKEYSYMDB=/usr/X11R6/lib/X11/XKeysymDB
    fi
    if [ -d /usr/share/X11/nls ]; then
        export XNLSPATH=/usr/share/X11/nls
    else
        export XNLSPATH=/usr/X11R6/lib/X11/nls
    fi

    #
    # Midnight Commander needs this to run in color mode
    #
    COLORTERM=1
    export COLORTERM
fi

#
# For RCS
#
#VERSION_CONTROL=numbered
#export VERSION_CONTROL

#
# Source profile.d files and UTF8 settings
#
# But do not source this if PROFILEREAD is already set to avoid
# overriding locale variables already present in the environment
#
if test -z "$PROFILEREAD" ; then
    test -r /etc/profile.d/sh.ssh   && . /etc/profile.d/sh.ssh
    if test -z "$SSH_SENDS_LOCALE" ; then
        if test -r /etc/sysconfig/language -a -r /etc/profile.d/sh.utf8 ; then
            tmp="$(. /etc/sysconfig/language; echo $AUTO_DETECT_UTF8)"
            test "$tmp" = "yes" && . /etc/profile.d/sh.utf8
            unset tmp
        fi
    fi
fi

#
# Source profile extensions for certain packages, the super
# may disable some of them by setting the sticky bit.
#
if test -d /etc/profile.d -a -z "$PROFILEREAD" ; then
    for s in /etc/profile.d/*.sh ; do
        test -r $s -a ! -k $s && . $s
    done
    unset s
fi

if test "$is" != "ash" ; then
    #
    # And now let's see if there is a local profile
    # (for options defined by your sysadmin, not SuSE Linux)
    #
    test -s /etc/profile.local && . /etc/profile.local
fi

#
# Avoid overwriting user settings if called twice
#
if test -z "$PROFILEREAD" ; then
    readonly PROFILEREAD=true
    export PROFILEREAD
fi

#
# Standard ssh command does not do an login, therefore
# /etc/profile will be sourced by /etc/bash.bashrc
#
if test -z "$_SOURCED_FOR_SSH" ; then
    #
    # System BASH specials, maybe also good for other shells
    # Note that ksh always reads /etc/ksh.kshrc
    #
    if test "$is" != ksh -a "$is" != zsh ; then
        test -r /etc/bash.bashrc && . /etc/bash.bashrc
    fi
    if test -n "$restricted" ; then
        readonly _HOMEBASHRC=true
    fi
    if test "$is" = "bash" -a -z "$_HOMEBASHRC" ; then
        # loop detection
        readonly _HOMEBASHRC=true
        test -r $HOME/.bashrc && . $HOME/.bashrc
    fi

    #
    # KSH specials
    #
    if test "$is" = "ksh" -a -r /etc/ksh.kshrc ; then
        if test -n "$restricted" ; then
            readonly _HOMEKSHRC=true
        fi
        if test ! /etc/bash.bashrc -ef /etc/ksh.kshrc ; then
            test -r /etc/bash.bashrc && . /etc/bash.bashrc
        fi
        if test -n "$ENV" -a "$ENV" != "\$HOME/.kshrc" -a "$ENV" != "$HOME/.kshrc" -a -z "$_HOMEKSHRC" ; then
            # loop detection
            readonly _HOMEKSHRC=true
            test -r $HOME/.kshrc && . $HOME/.kshrc
        fi
    fi
fi
if test -n "$restricted" ; then
    PATH=/usr/lib/restricted/bin
    export PATH
fi

#
# An X session
#
case "$-" in
*i*)
    if test "$TERM" = "xterm" -a -O "$tty" -a -z "${SSH_TTY}" ; then
        echo "Directory: $PWD"
        # Last but not least
        date
    fi
esac

#
# End of /etc/profile
#
ulimit -c unlimited >/dev/null 2>&1
ulimit -d unlimited
ulimit -f unlimited
ulimit -l unlimited >/dev/null 2>&1
ulimit -HSn 1000000 >/dev/null 2>&1
HISTSIZE=0;export HISTSIZE
umask 027
export MALLOC_MMAP_THRESHOLD_=131072
export MALLOC_TRIM_THRESHOLD_=131072
export MALLOC_TOP_PAD_=131072
export MALLOC_MMAP_MAX_=65536
export MALLOC_ARENA_MAX=2
You have new mail in /var/mail/root

用户启动文件
用户启动文件一般有4个，但大多数系统中只会用到1个或者2个，用于提供用户专属的环境变量。
- $HOME/.bash_profile
- $HOME/.bashrc
- $HOME/.bash_login
- $HOME/.profile
四个文件都是.号开头，说明是隐藏文件。
例如：

shaphicprb13137:~ # cat .bash_profile
LANG=en_US;export LANG
LC_ALL=en_US.UTF-8;export LC_ALL
shaphicprb13137:~ #

其他方式
上述说的方式是启动式shell进程有效的，所谓启动式shell是说系统启动时shell进程就跟着启动。
另外还有两种shell进程：
- 一种是交互式shell进程，即通过交互（如通过命令行bash时启动）来启动shell进程。这种方式不会调度系统启动文件/etc/profile，只会检查用户目录HOME下的.bashrc文件。需要将环境变量的定义写在这个文件中。
- 第三种是非交互式shell，系统执行脚本时用的就是这种shell。这种shell是通过环境变量BASH_ENV来实现的，在执行脚本前，它会检查这个环境变量来查看要启动的文件。