$PS1 转义 懂么？

layerbase

layerbase

\e
{dbian_chroot:+($debian_chroot)}

上面2个啥意思呢~

251316192

ubuntun在BASH启动过程中，以交互式登入并且终端为xterm时,PS1的值就是这样的。
1、BASH 的召唤过程。
INVOCATION
       A login shell is one whose first character of argument zero is a -, or one started with the --login option.

       An interactive shell is one started without non-option arguments and without the -c option whose standard input
       and error are both connected to terminals (as determined by isatty(3)), or one started with the -i option.  PS1
       is set and $- includes i if bash is interactive, allowing a shell script or a startup file to test this state.

       The following paragraphs describe how bash executes its startup files.  If any of the files exist but cannot be
       read, bash reports an error.  Tildes are expanded in file names as described below under Tilde Expansion in the
       EXPANSION section.

       When  bash  is invoked as an interactive login shell, or as a non-interactive shell with the --login option, it
       first reads and executes commands from the file /etc/profile, if that file exists.  After reading that file, it
       looks  for  ~/.bash_profile, ~/.bash_login, and ~/.profile, in that order, and reads and executes commands from
       the first one that exists and is readable.  The --noprofile option may be used when the  shell  is  started  to
       inhibit this behavior.

       When a login shell exits, bash reads and executes commands from the file ~/.bash_logout, if it exists.

       When  an  interactive  shell  that  is  not  a  login  shell  is started, bash reads and executes commands from
       /etc/bash.bashrc and ~/.bashrc, if these files exist.  This may be inhibited by using the --norc  option.   The
       --rcfile  file  option  will  force bash to read and execute commands from file instead of /etc/bash.bashrc and
       ~/.bashrc.

       When bash is started non-interactively, to run a shell script, for example, it looks for the variable  BASH_ENV
       in the environment, expands its value if it appears there, and uses the expanded value as the name of a file to
       read and execute.  Bash behaves as if the following command were executed:
              if [ -n "$BASH_ENV" ]; then . "$BASH_ENV"; fi
       but the value of the PATH variable is not used to search for the file name.

       If bash is invoked with the name sh, it tries to mimic the startup behavior of historical  versions  of  sh  as
       closely  as  possible,  while  conforming  to the POSIX standard as well.  When invoked as an interactive login
       shell, or a non-interactive shell with the --login option, it first attempts to read and execute commands  from
       /etc/profile and ~/.profile, in that order.  The --noprofile option may be used to inhibit this behavior.  When
       invoked as an interactive shell with the name sh, bash looks for the variable ENV, expands its value if  it  is
       defined,  and  uses  the expanded value as the name of a file to read and execute.  Since a shell invoked as sh
       does not attempt to read and execute commands from any other startup files, the --rcfile option has no  effect.
       A  non-interactive  shell  invoked  with  the  name  sh does not attempt to read any other startup files.  When
       invoked as sh, bash enters posix mode after the startup files are read.

       When bash is started in posix mode, as with the --posix command line option, it follows the POSIX standard  for
       startup  files.   In  this  mode, interactive shells expand the ENV variable and commands are read and executed
       from the file whose name is the expanded value.  No other startup files are read.

       Bash attempts to determine when it is being run with its standard input connected to a a network connection, as
       if  by  the remote shell daemon, usually rshd, or the secure shell daemon sshd.  If bash determines it is being
       run in this fashion, it reads and executes commands from ~/.bashrc and ~/.bashrc, if these files exist and  are
       readable.   It  will not do this if invoked as sh.  The --norc option may be used to inhibit this behavior, and
       the --rcfile option may be used to force another file to be read, but rshd does not generally invoke the  shell
       with those options or allow them to be specified.

       If  the  shell  is started with the effective user (group) id not equal to the real user (group) id, and the -p
       option is not supplied, no startup files are read, shell functions are not inherited from the environment,  the
       SHELLOPTS,  BASHOPTS, CDPATH, and GLOBIGNORE variables, if they appear in the environment, are ignored, and the
       effective user id is set to the real user id.  If the -p option is supplied at invocation, the startup behavior
       is the same, but the effective user id is not reset.
2、我们就以交互式登入为例跟踪其过程。
file: /etc/profile

1. 
   
2.   1 # /etc/profile: system-wide .profile file for the Bourne shell (sh(1))
   
3.   2 # and Bourne compatible shells (bash(1), ksh(1), ash(1), ...).
   
4.   3
   
5.   4 if [ -d /etc/profile.d ]; then
   
6.   5   for i in /etc/profile.d/*.sh; do
   
7.   6     if [ -r $i ]; then
   
8.   7       . $i
   
9.   8     fi
   
10.   9   done
    
11. 10   unset i
    
12. 11 fi
    
13. 12
    
14. 13 if [ "$PS1" ]; then
    
15. 14   if [ "$BASH" ]; then
    
16. 15     PS1='\u@\h:\w\$ '
    
17. 16     if [ -f /etc/bash.bashrc ]; then
    
18. 17     . /etc/bash.bashrc
    
19. 18     fi
    
20. 19   else
    
21. 20     if [ "`id -u`" -eq 0 ]; then
    
22. 21       PS1='# '
    
23. 22     else
    
24. 23       PS1='$ '
    
25. 24     fi
    
26. 25   fi
    
27. 26 fi
    
28. 27
    
29. 28 umask 022

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显然此时PS1未定义，只是source /etc/profile.d/*.sh, 在此目录下有个
file: /etc/profile.d/speechd-user-port.sh

1. 
   
2.   1 export SPEECHD_PORT=$(expr 6560 + $(getent passwd $USER | cut -f 3 -d :))

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这句话的意思就是用户的uid + 6560赋值给SPEECHED_PORT
file: ~/.profile

1. 
   
2.   1 # ~/.profile: executed by the command interpreter for login shells.
   
3.   2 # This file is not read by bash(1), if ~/.bash_profile or ~/.bash_login
   
4.   3 # exists.
   
5.   4 # see /usr/share/doc/bash/examples/startup-files for examples.
   
6.   5 # the files are located in the bash-doc package.
   
7.   6
   
8.   7 # the default umask is set in /etc/profile; for setting the umask
   
9.   8 # for ssh logins, install and configure the libpam-umask package.
   
10.   9 #umask 022
    
11. 10
    
12. 11 # if running bash
    
13. 12 if [ -n "$BASH_VERSION" ]; then
    
14. 13     # include .bashrc if it exists
    
15. 14     if [ -f "$HOME/.bashrc" ]; then
    
16. 15     . "$HOME/.bashrc"
    
17. 16     fi
    
18. 17 fi
    
19. 18
    
20. 19 # set PATH so it includes user's private bin if it exists
    
21. 20 if [ -d "$HOME/bin" ] ; then
    
22. 21     PATH="$HOME/bin:$PATH"
    
23. 22 fi

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source ~/.bashrc 然后添加了用户自己的bin目录到PATH
file: ./bashrc

1. 
   
2.   1 # ~/.bashrc: executed by bash(1) for non-login shells.
   
3.   2 # see /usr/share/doc/bash/examples/startup-files (in the package bash-doc)
   
4.   3 # for examples
   
5.   4
   
6.   5 # If not running interactively, don't do anything
   
7.   6 [ -z "$PS1" ] && return
   
8.   7
   
9.   8 # don't put duplicate lines in the history. See bash(1) for more options
   
10.   9 # ... or force ignoredups and ignorespace
    
11. 10 HISTCONTROL=ignoredups:ignorespace
    
12. 11
    
13. 12 # append to the history file, don't overwrite it
    
14. 13 shopt -s histappend
    
15. 14
    
16. 15 # for setting history length see HISTSIZE and HISTFILESIZE in bash(1)
    
17. 16 HISTSIZE=1000
    
18. 17 HISTFILESIZE=2000
    
19. 18
    
20. 19 # check the window size after each command and, if necessary,
    
21. 20 # update the values of LINES and COLUMNS.
    
22. 21 shopt -s checkwinsize
    
23. 22
    
24. 23 # make less more friendly for non-text input files, see lesspipe(1)
    
25. 24 [ -x /usr/bin/lesspipe ] && eval "$(SHELL=/bin/sh lesspipe)"
    
26. 25
    
27. 26 # set variable identifying the chroot you work in (used in the prompt below)
    
28. 27 if [ -z "$debian_chroot" ] && [ -r /etc/debian_chroot ]; then
    
29. 28     debian_chroot=$(cat /etc/debian_chroot)
    
30. 29 fi
    
31. 30
    
32. 31 # set a fancy prompt (non-color, unless we know we "want" color)
    
33. 32 case "$TERM" in
    
34. 33     xterm-color) color_prompt=yes;;
    
35. 34 esac
    
36. 35
    
37. 36 # uncomment for a colored prompt, if the terminal has the capability; turned
    
38. 37 # off by default to not distract the user: the focus in a terminal window
    
39. 38 # should be on the output of commands, not on the prompt
    
40. 39 #force_color_prompt=yes
    
41. 40
    
42. 41 if [ -n "$force_color_prompt" ]; then
    
43. 42     if [ -x /usr/bin/tput ] && tput setaf 1 >&/dev/null; then
    
44. 43     # We have color support; assume it's compliant with Ecma-48
    
45. 44     # (ISO/IEC-6429). (Lack of such support is extremely rare, and such
    
46. 45     # a case would tend to support setf rather than setaf.)
    
47. 46     color_prompt=yes
    
48. 47     else
    
49. 48     color_prompt=
    
50. 49     fi
    
51. 50 fi
    
52. 51
    
53. 52 if [ "$color_prompt" = yes ]; then
    
54. 53     PS1='${debian_chroot:+($debian_chroot)}\[\033[01;32m\]\u@\h\[\033[00m\]:\[\033[01;34m\]\w\[\033[00m\]\$ '
    
55. 54 else
    
56. 55     PS1='${debian_chroot:+($debian_chroot)}\u@\h:\w\$ '
    
57. 56 fi
    
58. 57 unset color_prompt force_color_prompt
    
59. 58
    
60. 59 # If this is an xterm set the title to user@host:dir
    
61. 60 case "$TERM" in
    
62. 61 xterm*|rxvt*)
    
63. 62     PS1="\[\e]0;${debian_chroot:+($debian_chroot)}\u@\h: \w\a\]$PS1"
    
64. 63     ;;
    
65. 64 *)
    
66. 65     ;;
    
67. 66 esac
    
68. 67
    
69. 68 # enable color support of ls and also add handy aliases
    
70. 69 if [ -x /usr/bin/dircolors ]; then
    
71. 70     test -r ~/.dircolors && eval "$(dircolors -b ~/.dircolors)" || eval "$(dircolors -b)"
    
72. 71     alias ls='ls --color=auto'
    
73. 72     #alias dir='dir --color=auto'
    
74. 73     #alias vdir='vdir --color=auto'
    
75. 74
    
76. 75     alias grep='grep --color=auto'
    
77. 76     alias fgrep='fgrep --color=auto'
    
78. 77     alias egrep='egrep --color=auto'
    
79. 78 fi
    
80. 79
    
81. 80 # some more ls aliases
    
82. 81 alias ll='ls -alF'
    
83. 82 alias la='ls -A'
    
84. 83 alias l='ls -CF'
    
85. 84
    
86. 85 # Alias definitions.
    
87. 86 # You may want to put all your additions into a separate file like
    
88. 87 # ~/.bash_aliases, instead of adding them here directly.
    
89. 88 # See /usr/share/doc/bash-doc/examples in the bash-doc package.
    
90. 89
    
91. 90 if [ -f ~/.bash_aliases ]; then
    
92. 91     . ~/.bash_aliases
    
93. 92 fi
    
94. 93
    
95. 94 # enable programmable completion features (you don't need to enable
    
96. 95 # this, if it's already enabled in /etc/bash.bashrc and /etc/profile
    
97. 96 # sources /etc/bash.bashrc).
    
98. 97 if [ -f /etc/bash_completion ] && ! shopt -oq posix; then
    
99. 98     . /etc/bash_completion
    
100. 99 fi

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把PS1设置部分抓出来分析

1. 52 if [ "$color_prompt" = yes ]; then
   
2. 53     PS1='${debian_chroot:+($debian_chroot)}\[\033[01;32m\]\u@\h\[\033[00m\]:\[\033[01;34m\]\w\[\033[00m\]\$ '
   
3. 54 else
   
4. 55     PS1='${debian_chroot:+($debian_chroot)}\u@\h:\w\$ '
   
5. 56 fi
   
6. 57 unset color_prompt force_color_prompt
   
7. 58
   
8. 59 # If this is an xterm set the title to user@host:dir
   
9. 60 case "$TERM" in
   
10. 61 xterm*|rxvt*)
    
11. 62     PS1="\[\e]0;${debian_chroot:+($debian_chroot)}\u@\h: \w\a\]$PS1"
    
12. 63     ;;
    
13. 64 *)
    
14. 65     ;;
    
15. 66 esac

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这个debian_chroot解释如下
Using The chroot Environments on Debian Machines
To use the chroot environments set up on the Debian machines run the dchroot program. In each chroot, there is a file /etc/debian_chroot, the contents of which will tell you which chroot you are in.
大致意思是用来在多个根文件系统的切换，以表示你在哪个根文件系统。
基本上我们只挂一个根文件系统，所以debian_chroot空。
${debian_chroot:+($debian_chroot)}的含义
表达式替换var=${str:+expr} str没设置var=expr, str为空,则var为空,str有值var=str
这样${debian_chroot:+($debian_chroot)}就为空了
\[\033[01;32m这类东西表示终端颜色转义
52-56行意思就很明确是否提示符要带颜色显示。中间的${debian_chroot:+($debian_chroot)}表示在那个根文件系统。
在后面的62行代码开始，表示xterm就是图形终端了。在ubuntu一般就是伪终端了输入who看到的pts什么的就是了。
一般X windows在ubuntu我看到的是在tty7加载。
\[\e]0;${debian_chroot:+($debian_chroot)}\u@\h: \w\a
这一大串就是你打开终端的标题.\[\e]0;就是终端颜色取消，你打开的终端标题栏就看到了。
\e]0;title\a是标题表示模式匹配
只须用您希望其出现在 xterm 标题栏中的文字替换子串 "title" 即可，
您能够将 bash 转义序列插入标题栏中,他将用户名、主机名和当前工作目录显示在标题栏中。

顺便提一句，确保用 "\[" 和 "\]" 将您的标题栏序列括起来（因为就终端而言，这个序列是非打印序列）。

cai120120-pb

原来如此啊