引子
刚才碰见了，其实一直有这个想法，想搞清楚系统下每一个文件都是干啥的。看的懂每一个系统自带的脚本是啥子意思。这次又碰见了这个文件我打算就从它开始，读懂它（/etc/bashrc）都干了什么。
1 # /etc/bashrc
2
3 # System wide functions and aliases
4 # Environment stuff goes in /etc/profile
5
6 # It‘s NOT a good idea to change this file unless you know what you
7 # are doing. It‘s much better to create a custom.sh shell script in
8 # /etc/profile.d/ to make custom changes to your environment, as this
9 # will prevent the need for merging in future updates.
10
11 # are we an interactive shell?
12 if [ "$PS1" ]; then
13 if [ -z "$PROMPT_COMMAND" ]; then
14 case $TERM in
15 xterm*)
16 if [ -e /etc/sysconfig/bash-prompt-xterm ]; then
17 PROMPT_COMMAND=/etc/sysconfig/bash-prompt-xterm
18 else
19 PROMPT_COMMAND=‘printf "\033]0;%s@%s:%s\007" "${USER}" "${HOSTNAME%%.*}" "${PWD/#$HOME/~}"‘
20 fi
21 ;;
22 screen)
23 if [ -e /etc/sysconfig/bash-prompt-screen ]; then
24 PROMPT_COMMAND=/etc/sysconfig/bash-prompt-screen
25 else
26 PROMPT_COMMAND=‘printf "\033]0;%s@%s:%s\033\\" "${USER}" "${HOSTNAME%%.*}" "${PWD/#$HOME/~}"‘
27 fi
28 ;;
29 *)
30 [ -e /etc/sysconfig/bash-prompt-default ] && PROMPT_COMMAND=/etc/sysconfig/bash-prompt-default
31 ;;
32 esac
33 fi
34 # Turn on checkwinsize
35 shopt -s checkwinsize
36 [ "$PS1" = "\\s-\\v\\\$ " ] && PS1="[\u@\h \W]\\$ "
37 # You might want to have e.g. tty in prompt (e.g. more virtual machines)
38 # and console windows
39 # If you want to do so, just add e.g.
40 # if [ "$PS1" ]; then
41 # PS1="[\u@\h:\l \W]\\$ "
42 # fi
43 # to your custom modification shell script in /etc/profile.d/ directory
44 fi
45
46 if ! shopt -q login_shell ; then # We‘re not a login shell
47 # Need to redefine pathmunge, it get‘s undefined at the end of /etc/profile
48 pathmunge () {
49 case ":${PATH}:" in
50 *:"$1":*)
51 ;;
52 *)
53 if [ "$2" = "after" ] ; then
54 PATH=$PATH:$1
55 else
56 PATH=$1:$PATH
57 fi
58 esac
59 }
60
61 # By default, we want umask to get set. This sets it for non-login shell.
62 # Current threshold for system reserved uid/gids is 200
63 # You could check uidgid reservation validity in
64 # /usr/share/doc/setup-*/uidgid file
65 if [ $UID -gt 199 ] && [ "`id -gn`" = "`id -un`" ]; then
66 umask 002
67 else
68 umask 022
69 fi
70
71 # Only display echos from profile.d scripts if we are no login shell
72 # and interactive - otherwise just process them to set envvars
73 for i in /etc/profile.d/*.sh; do
74 if [ -r "$i" ]; then
75 if [ "$PS1" ]; then
76 . "$i"
77 else
78 . "$i" >/dev/null 2>&1
79 fi
80 fi
81 done
82
83 unset i
84 unset pathmunge
85 fi
86 # vim:ts=4:sw=4我“纯手工”给系统添加用户时，登陆进去发现有点异样。
[root@hp430G2 shell]# su - hive -bash-4.1$ echo $PS1 \s-\v\$ ..... [hive@hp430G2 ~]$ echo $PS1 [\u@\h \W]\$
造成这个的原因是我复制文件的时候没有操作好，导致了隐藏文件（~/.bashrc）没有执行，该文件运行了另外一个文件（/etc/bashrc）。
尝试分析
前11行是注释，由“空行”分为四段。第一段是该文件的名称、系统位置。第二段是说明部分，“系统中的函数、别名在这里定义”，“环境变量在 /etc/profile 里边定义”。第三段是个温馨提示。第四段是个“调皮话”（就位置分析有可能是下文的，也有可能是上文的；暂且不管）。
12-44
看看12行到44行都干什么了。
本文出自 “小崔的实验笔记” 博客，谢绝转载！
原文：http://sunnybay.blog.51cto.com/2249903/1854160