I'm not sure that these escape sequences strictly qualify as "ANSI Escape Sequences," but in practice their use is almost identical so I've included them in this chapter.
Non-printing escape sequences can be used to produce interesting effects in prompts. To use these escape sequences, you need to enclose them in \[ and \] (as discussed in Section 3.4, telling Bash to ignore this material while calculating the size of the prompt. Failing to include these delimiters results in line editing code placing the cursor incorrectly because it doesn't know the actual size of the prompt. Escape sequences must also be preceded by \033[ in Bash prior to version 2, or by either \033[ or \e[ in later versions.
If you try to change the title bar of your Xterm with your prompt when you're at the console, you'll produce garbage in your prompt. To avoid this, test the TERM environment variable to tell if your prompt is going to be in an Xterm.
function proml
{
case $TERM in
xterm*)
local TITLEBAR='\[\033]0;\u@\h:\w\007\]'
;;
*)
local TITLEBAR=''
;;
esac
PS1="${TITLEBAR}\
[\$(date +%H%M)]\
[\u@\h:\w]\
\$ "
PS2='> '
PS4='+ '
} |
This is a function that can be incorporated into ~/.bashrc. The function name could then be called to execute the function. The function, like the PS1 string, is stored in the environment. Once the PS1 string is set by the function, you can remove the function from the environment with unset proml. Since the prompt can't change from being in an Xterm to being at the console, the TERM variable isn't tested every time the prompt is generated. I used continuation markers (backslashes) in the definition of the prompt, to allow it to be continued on multiple lines. This improves readability, making it easier to modify and debug.
The first step in creating this prompt is to test if the shell we're starting is an xterm or not: if it is, the shell variable (${TITLEBAR}) is defined. It consists of the appropriate escape sequences, and \u@\h:\w, which puts <user>@<machine>:<working directory> in the Xterm title bar. This is particularly useful with minimized Xterms, making them more rapidly identifiable. The other material in this prompt should be familiar from previous prompts we've created.
The only drawback to manipulating the Xterm title bar like this occurs when you log into a system on which you haven't set up the title bar hack: the Xterm will continue to show the information from the previous system that had the title bar hack in place.
A suggestion from Charles Lepple (<clepple at negativezero dot org>) on setting the window title of the Xterm and the title of the corresponding icon separately. He uses this under WindowMaker because the title that's appropriate for an Xterm is usually too long for a 64x64 icon. "\[\e]1;icon-title\007\e]2;main-title\007\]". He says to set this in the prompt command because "I tried putting the string in PS1, but it causes flickering under some window managers because it results in setting the prompt multiple times when you are editing a multi-line command (at least under bash 1.4.x -- and I was too lazy to fully explore the reasons behind it)." I had no trouble with it in the PS1 string, but didn't use any multi-line commands. He also points out that it works under xterm, xwsh, and dtterm, but not gnome-terminal (which uses only the main title). I also found it to work with rxvt, but not kterm.