在Linux上開發或者部署應用時,免不了要設置配置文件,好比安裝JDK,須要爲java可執行文件配置環境變量。
大多數時候咱們不須要關注shell,可是當你執行"sudo su" 命令時,發現並不能同時把環境變量切換到root的環境;當你執行遠程shell文件-"ssh who@host file.sh",發現不能加載環境配置文件時,那麼你就要搞清楚bash的環境配置文件加載原理來搞定這些問題。
本文所有是基於CentOS系統寫的,其它Linux發行版本可能略有差別。java
bash allows two synonyms for .bash_profile: .bash_login, derived from the C shell’s file named .login, and .profile, derived from the Bourne shell and Korn shell files named .profile. Only one of these three is read when you log in. If .bash_profile doesn’t exist in your home directory, then bash will look for .bash_login. If that doesn’t exist it will look for .profile.
One advantage of bash’s ability to look for either synonym is that you can retain your .profile if you have been using the Bourne shell. If you need to add bash-specific commands, you can put them in .bash_profile followed by the command source .profile. When you log in, all the bash-specific commands will be executed and bash will source .profile, executing the remaining commands. If you decide to switch to using the Bourne shell you don’t have to modify your existing files. A similar approach was intended for .bash_login and the C shell .login, but due to differences in the basic syntax of the shells, this is not a good idea.shell
翻譯以下:bash
bash容許.bash_profile 有兩個同義詞:app
- .bash_login, 從C shell的.login文件衍生而來。
- .profile, 從Bourne shell 和 Korn shell 的.profile文件。
當你登陸shell的時候,這三個文件中僅有一個會被讀取。若是.bash_profile在你的用戶主目錄(home)下不存在,那麼bash將會查找.bash_login。若是.bash_login不存在,那麼bash將會查找.profile。less
bash可以查找任意一個同義文件這種能力的優點就是--若是你使用了Bourne shell,可以保留你的.profile。若是你須要添加具體bash的命令,你能夠把它們放進.bash_profile文件,而且執行命令source .profile。
若是你想切換到Bourne shell,你沒必要修改你已存在文件。對於.bash_login和C shell .login也是相同的,可是因爲shell的基礎語法存在差別,這麼作並不推薦。ssh
根本緣由是爲了兼容各類shell。ide
讀取環境配置文件以前,須要先區分login shell和non-login shell,由於這兩種shell讀取的配置文件不同。ui
基本原理到此已經結束,若是你還意猶未盡,再繼續看CentOS系統的/etc/profile文件和~/.bash_profile文件的內容:this
# /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 export GREP_OPTIONS=--color=auto
# .bash_profile # Get the aliases and functions if [ -f ~/.bashrc ]; then . ~/.bashrc fi # User specific environment and startup programs PATH=$PATH:$HOME/bin export PATH