Linux 环境变量

本文主要是介绍Linux 环境变量，对大家解决编程问题具有一定的参考价值，需要的程序猿们随着小编来一起学习吧！

1. 综述

Linux下的环境变量分为两种，系统变量和用户变量。

1.1 系统级变量

以Ubuntu系统为例，我们使用 vim 打开文件 /etc/environment,内容如下：

PATH="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin"

可以看到该文件下保存了基本的PATH 环境变量。
另外一个保存系统级环境变量的文件是：/etc/profile,内容如下：

# /etc/profile: system-wide .profile file for the Bourne shell (sh(1))
# and Bourne compatible shells (bash(1), ksh(1), ash(1), ...).

if [ "${PS1-}" ]; then
  if [ "${BASH-}" ] && [ "$BASH" != "/bin/sh" ]; then
    # The file bash.bashrc already sets the default PS1.
    # PS1='\h:\w\$ '
    if [ -f /etc/bash.bashrc ]; then
      . /etc/bash.bashrc
    fi
  else
    if [ "`id -u`" -eq 0 ]; then
      PS1='# '
    else
      PS1='$ '
    fi
  fi
fi

if [ -d /etc/profile.d ]; then
  for i in /etc/profile.d/*.sh; do
    if [ -r $i ]; then
      . $i
    fi
  done
  unset i
fi

如上代码大致执行的功能是执行文件 /etc/bash.bashrc 及/etc/profile.d 下的所有文件，初始化相关Shell 脚本的配置。

以上两个文件在系统初始化时执行，修改后需要重启系统，重新加载配置，也可以使用如下命令重新执行下配置文件代码

在这里插入代码片

1.2 用户级

在用户目录下有两个文件 .bashrc .profile，如下图：

在这两个文件中保存了用户相关的环境变量配置。

如下是 .bashrc 文件的内容

# ~/.bashrc: executed by bash(1) for non-login shells.
# see /usr/share/doc/bash/examples/startup-files (in the package bash-doc)
# for examples

# If not running interactively, don't do anything
[ -z "$PS1" ] && return

# don't put duplicate lines in the history. See bash(1) for more options
# ... or force ignoredups and ignorespace
HISTCONTROL=ignoredups:ignorespace

# append to the history file, don't overwrite it
shopt -s histappend

# for setting history length see HISTSIZE and HISTFILESIZE in bash(1)
HISTSIZE=1000
HISTFILESIZE=2000

# check the window size after each command and, if necessary,
# update the values of LINES and COLUMNS.
shopt -s checkwinsize

# make less more friendly for non-text input files, see lesspipe(1)
[ -x /usr/bin/lesspipe ] && eval "$(SHELL=/bin/sh lesspipe)"

# set variable identifying the chroot you work in (used in the prompt below)
if [ -z "$debian_chroot" ] && [ -r /etc/debian_chroot ]; then
    debian_chroot=$(cat /etc/debian_chroot)
fi

# set a fancy prompt (non-color, unless we know we "want" color)
case "$TERM" in
    xterm-color) color_prompt=yes;;
esac

# uncomment for a colored prompt, if the terminal has the capability; turned
# off by default to not distract the user: the focus in a terminal window
# should be on the output of commands, not on the prompt
#force_color_prompt=yes

if [ -n "$force_color_prompt" ]; then
    if [ -x /usr/bin/tput ] && tput setaf 1 >&/dev/null; then
        # We have color support; assume it's compliant with Ecma-48
        # (ISO/IEC-6429). (Lack of such support is extremely rare, and such
        # a case would tend to support setf rather than setaf.)
        color_prompt=yes
    else
        color_prompt=
    fi
fi

if [ "$color_prompt" = yes ]; then
    PS1='${debian_chroot:+($debian_chroot)}\[\033[01;32m\]\u@\h\[\033[00m\]:\[\033[01;34m\]\w\[\033[00m\]\$ '
else
    PS1='${debian_chroot:+($debian_chroot)}\u@\h:\w\$ '
fi
unset color_prompt force_color_prompt

# If this is an xterm set the title to user@host:dir
case "$TERM" in
xterm*|rxvt*)
    PS1="\[\e]0;${debian_chroot:+($debian_chroot)}\u@\h: \w\a\]$PS1"
    ;;
*)
    ;;
esac

# enable color support of ls and also add handy aliases
if [ -x /usr/bin/dircolors ]; then
    test -r ~/.dircolors && eval "$(dircolors -b ~/.dircolors)" || eval "$(dircolors -b)"
    alias ls='ls --color=auto'
    #alias dir='dir --color=auto'
    #alias vdir='vdir --color=auto'

    alias grep='grep --color=auto'
    alias fgrep='fgrep --color=auto'
    alias egrep='egrep --color=auto'
fi

# some more ls aliases
alias ll='ls -alF'
alias la='ls -A'
alias l='ls -CF'

# Alias definitions.
# You may want to put all your additions into a separate file like
# ~/.bash_aliases, instead of adding them here directly.
# See /usr/share/doc/bash-doc/examples in the bash-doc package.

if [ -f ~/.bash_aliases ]; then
    . ~/.bash_aliases
fi


# enable programmable completion features (you don't need to enable
# this, if it's already enabled in /etc/bash.bashrc and /etc/profile
# sources /etc/bash.bashrc).
#if [ -f /etc/bash_completion ] && ! shopt -oq posix; then
#    . /etc/bash_completion
#fi

为了搞懂如上脚本，我们需要搞懂如下几个命令：

• shopt

root@iZrj98gfe049j7f5i96hsuZ:~# shopt --help
shopt: shopt [-pqsu] [-o] [optname ...]
    Set and unset shell options.
    
    Change the setting of each shell option OPTNAME.  Without any option
    arguments, list each supplied OPTNAME, or all shell options if no
    OPTNAMEs are given, with an indication of whether or not each is set.
    
    Options:
      -o	restrict OPTNAMEs to those defined for use with `set -o'
      -p	print each shell option with an indication of its status
      -q	suppress output
      -s	enable (set) each OPTNAME
      -u	disable (unset) each OPTNAME
    
    Exit Status:
    Returns success if OPTNAME is enabled; fails if an invalid option is
    given or OPTNAME is disabled.

该命令设置Shell 相关配置项。设置为 启用或不启用。

用于设置的项包括：

root@iZrj98gfe049j7f5i96hsuZ:~# shopt
autocd         	off
assoc_expand_once	off
cdable_vars    	off
cdspell        	off
checkhash      	off
checkjobs      	off
checkwinsize   	on
cmdhist        	on
compat31       	off
compat32       	off
compat40       	off
compat41       	off
compat42       	off
compat43       	off
compat44       	off
complete_fullquote	on
direxpand      	off
dirspell       	off
dotglob        	off
execfail       	off
expand_aliases 	on
extdebug       	off
extglob        	on
extquote       	on
failglob       	off
force_fignore  	on
globasciiranges	on
globstar       	off
gnu_errfmt     	off
histappend     	on
histreedit     	off
histverify     	off
hostcomplete   	off
huponexit      	off
inherit_errexit	off
interactive_comments	on
lastpipe       	off
lithist        	off
localvar_inherit	off
localvar_unset 	off
login_shell    	on
mailwarn       	off
no_empty_cmd_completion	off
nocaseglob     	off
nocasematch    	off
nullglob       	off
progcomp       	on
progcomp_alias 	off
promptvars     	on
restricted_shell	off
shift_verbose  	off
sourcepath     	on
xpg_echo       	off

• set unset 命令

这是一对内建的Unix Shell 命令，用于设置或取消Shell 变量。

• alias

该命令用于设置指令的别名。

• test

Shell中的 test 命令用于检查某个条件是否成立，它可以进行数值、字符和文件三个方面的测试。

总结一下 .profile 文件主要完成对于历史记录，配色及部分指令别名的设置。

如下是 .profile 文件的内容

# ~/.profile: executed by Bourne-compatible login shells.
  
if [ "$BASH" ]; then
  if [ -f ~/.bashrc ]; then
    . ~/.bashrc
  fi
fi

mesg n 2> /dev/null || true

该文件调用 .bashrc 文件实现Shell 配置。

这篇关于Linux 环境变量的文章就介绍到这儿，希望我们推荐的文章对大家有所帮助，也希望大家多多支持为之网！