Debian .bashrc：提示PS1

Question

Let's say I'm on a fresh install of Debian, Jessie (or Wheezy). As a regular user, I've got the prompt defined in the /etc/bash.bashrc file, eventually override by the one in my /home/foobar/.bashrc

Ok, cool, so I've got something like that: foobar@myserver:~$ Now, I'm trying to understand the code below:

# 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

As you can see, the PS1 variable (= the prompt) seems to be overrided again (cause yeah I'm in a xterm ). But I can't get why we have another $PS1 on the end of the line!

In order to get this, I've put 3 letters a b c in this line :

PS1="a\[\e]0;${debian_chroot:+($debian_chroot)}\u@\h: \w\a\]b$PS1 c"

And now, I have the strange prompt below:

abfoobar@myserver:~$  c

So it seems that the almost entire line is not use, everything between the brakets.

• Is that a sort of conditional statement?
• What is really the purpose of this line?
• Why the comment talk about the title of the xterm windows but seems to only override the PS1? I'm running this xterm through PuTTY ; in ubuntu, this line is quite different PROMPT_COMMAND='echo -ne "\\033]0;${USER}@${HOSTNAME}: ${PWD}\\007"'

Answer 1

the part between \\[ \\] seems to be an escape sequence which is handled by terminal : ESC ] which is named OSC for Operating System Commands in following link xterm escape sequence

OSC Ps ; Pt ST
      Set Text Parameters.  For colors and font, if Pt is a "?", the
      control sequence elicits a response which consists of the con-
      trol sequence which would set the corresponding value.  The
      dtterm control sequences allow you to determine the icon name
      and window title.
        Ps = 0  -> Change Icon Name and Window Title to Pt.

It is to change xterm window title.

As the window title contains the current working directory setting the prompt allows to update the title when changing directory after cd command.