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<h2><font face="Helvetica"><a name="s6">6. ANSI Escape Sequences: Colours and Cursor Movement</a></font></h2>
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<h2><font face="Helvetica"><a name="ss6.1">6.1 Colours</a>
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<p><font face="Helvetica">As mentioned before, non-printing escape sequences have to be enclosed in
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<b>\[\033[</b> and <b>\]</b>. For colour escape sequences, they should
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also be followed by a lowercase <b>m</b>.
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</p><p><font face="Helvetica">If you try out the following prompts in an xterm and find that you aren't
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seeing the colours named, check out your ~/.Xdefaults file (and
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possibly its bretheren) for lines like "XTerm*Foreground: BlanchedAlmond".
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This can be commented out by placing an exclamation mark ("!") in front of
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it. Of course, this will also be dependent on what terminal emulator
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you're using. This is the likeliest place that your term foreground
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colours would be overridden.
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</p><p><font face="Helvetica">To include blue text in the prompt:
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</p><blockquote><code>
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<pre><font face="Helvetica">PS1="\[\033[34m\][\$(date +%H%M)][\u@\h:\w]$ "
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<p><font face="Helvetica">The problem with this prompt is that the blue colour that starts with the
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34 colour code is never switched back to the regular colour, so any text
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you type after the prompt is still in the colour of the prompt. This is
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also a dark shade of blue, so combining it with the <b>bold</b> code
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</p><blockquote><code>
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<pre><font face="Helvetica">PS1="\[\033[1;34m\][\$(date +%H%M)][\u@\h:\w]$\[\033[0m\] "
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</p><p><font face="Helvetica">The prompt is now in light blue, and it ends by switching the colour
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back to nothing (whatever foreground colour you had previously).
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</p><p><font face="Helvetica">Here are the rest of the colour equivalences:
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</p><blockquote><code>
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<pre><font face="Helvetica">Black 0;30 Dark Gray 1;30
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Blue 0;34 Light Blue 1;34
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Green 0;32 Light Green 1;32
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Cyan 0;36 Light Cyan 1;36
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Red 0;31 Light Red 1;31
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Purple 0;35 Light Purple 1;35
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Brown 0;33 Yellow 1;33
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Light Gray 0;37 White 1;37
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</p><p><font face="Helvetica">Daniel Dui (ddui@iee.org) points out that to be strictly accurate, we must
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mention that the list above is for colours at the console. In an xterm,
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the code <b>1;31</b> isn't "Light Red," but "Bold Red." This is true of
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</p><p><font face="Helvetica">You can also set background colours by using 44 for Blue background, 41 for
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a Red background, etc. There are no bold background colours. Combinations
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can be used, like Light Red text on a Blue background:
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<b>\[\033[44;1;31m\]</b>, although setting the colours separately seems
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to work better (ie. <b>\[\033[44m\]\[\033[1;31m\]</b>). Other codes
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available include 4: Underscore, 5: Blink, 7: Inverse, and 8: Concealed.
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</p><p><font face="Helvetica"><b>Aside:</b> Many people (myself included) object strongly to the
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"blink" attribute. Fortunately, it doesn't work in any terminal emulators
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that I'm aware of - but it will still work on the console. And, if you
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were wondering (as I did) "What use is a 'Concealed' attribute?!" - I saw
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it used in an example shell script (not a prompt) to allow someone to type
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in a password without it being echoed to the screen.
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</p><p><font face="Helvetica">Based on a prompt called "elite2" in the Bashprompt package (which I
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have modified to work better on a standard console, rather than with the
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special xterm fonts required to view the original properly), this is a
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prompt I've used a lot:
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<pre><font face="Helvetica">
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local GRAY="\[\033[1;30m\]"
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local LIGHT_GRAY="\[\033[0;37m\]"
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local CYAN="\[\033[0;36m\]"
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local LIGHT_CYAN="\[\033[1;36m\]"
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local TITLEBAR='\[\033]0;\u@\h:\w\007\]'
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local GRAD1=$(tty|cut -d/ -f3)
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$GRAY-$CYAN-$LIGHT_CYAN(\
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$CYAN\u$GRAY@$CYAN\h\
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$LIGHT_CYAN)$CYAN-$LIGHT_CYAN(\
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$CYAN\#$GRAY/$CYAN$GRAD1\
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$LIGHT_CYAN)$CYAN-$LIGHT_CYAN(\
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$CYAN\$(date +%H%M)$GRAY/$CYAN\$(date +%d-%b-%y)\
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$LIGHT_CYAN)$CYAN-$GRAY-\
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$GRAY-$CYAN-$LIGHT_CYAN(\
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$CYAN\$$GRAY:$CYAN\w\
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$LIGHT_CYAN)$CYAN-$GRAY-$LIGHT_GRAY "
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PS2="$LIGHT_CYAN-$CYAN-$GRAY-$LIGHT_GRAY "
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</p><p><font face="Helvetica">I define the colours as temporary shell variables in the name of
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readability. It's easier to work with. The "GRAD1" variable is a check to
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determine what terminal you're on. Like the test to determine if you're
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working in an Xterm, it only needs to be done once. The prompt you see
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look like this, except in colour:
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</p><blockquote><code>
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<pre><font face="Helvetica">--(giles@nikola)-(75/ttyp7)-(1908/12-Oct-98)--
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</p><p><font face="Helvetica">To help myself remember what colours are available, I wrote the following
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script which echoes all the colours to screen:
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<pre><font face="Helvetica">#!/bin/bash
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# This file echoes a bunch of colour codes to the terminal to demonstrate
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# what's available. Each line is one colour on black and gray
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# backgrounds, with the code in the middle. Verified to work on white,
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# black, and green BGs (2 Dec 98).
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echo " On Light Gray: On Black:"
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echo -e "\033[47m\033[1;37m White \033[0m\
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\033[40m\033[1;37m White \033[0m"
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echo -e "\033[47m\033[37m Light Gray \033[0m\
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\033[40m\033[37m Light Gray \033[0m"
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echo -e "\033[47m\033[1;30m Gray \033[0m\
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\033[40m\033[1;30m Gray \033[0m"
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echo -e "\033[47m\033[30m Black \033[0m\
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\033[40m\033[30m Black \033[0m"
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echo -e "\033[47m\033[31m Red \033[0m\
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\033[40m\033[31m Red \033[0m"
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echo -e "\033[47m\033[1;31m Light Red \033[0m\
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\033[40m\033[1;31m Light Red \033[0m"
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echo -e "\033[47m\033[32m Green \033[0m\
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\033[40m\033[32m Green \033[0m"
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echo -e "\033[47m\033[1;32m Light Green \033[0m\
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\033[40m\033[1;32m Light Green \033[0m"
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echo -e "\033[47m\033[33m Brown \033[0m\
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\033[40m\033[33m Brown \033[0m"
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echo -e "\033[47m\033[1;33m Yellow \033[0m\
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\033[40m\033[1;33m Yellow \033[0m"
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echo -e "\033[47m\033[34m Blue \033[0m\
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\033[40m\033[34m Blue \033[0m"
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echo -e "\033[47m\033[1;34m Light Blue \033[0m\
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\033[40m\033[1;34m Light Blue \033[0m"
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echo -e "\033[47m\033[35m Purple \033[0m\
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\033[40m\033[35m Purple \033[0m"
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echo -e "\033[47m\033[1;35m Pink \033[0m\
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\033[40m\033[1;35m Pink \033[0m"
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echo -e "\033[47m\033[36m Cyan \033[0m\
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\033[40m\033[36m Cyan \033[0m"
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echo -e "\033[47m\033[1;36m Light Cyan \033[0m\
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\033[40m\033[1;36m Light Cyan \033[0m"
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</p><h2><font face="Helvetica"><a name="ss6.2">6.2 Cursor Movement</a>
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<p><font face="Helvetica">ANSI escape sequences allow you to move the cursor around the screen at
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will. This is more useful for full screen user interfaces generated by
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shell scripts, but can also be used in prompts. The movement escape
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sequences are as follows:
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</p><blockquote><code>
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<pre><font face="Helvetica">- Position the Cursor:
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\033[<L>;<C>H
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\033[<L>;<C>f
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puts the cursor at line L and column C.
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- Move the cursor up N lines:
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- Move the cursor down N lines:
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- Move the cursor forward N columns:
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- Move the cursor backward N columns:
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- Clear the screen, move to (0,0):
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- Erase to end of line:
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- Save cursor position:
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- Restore cursor position:
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</p><p><font face="Helvetica">The latter two codes are NOT honoured by many terminal emulators. The only
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ones that I'm aware of that do are xterm and nxterm - even though the
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majority of terminal emulators are based on xterm code. As far as I can
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tell, rxvt, kvt, xiterm, and Eterm do not support them. They are supported
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</p><p><font face="Helvetica">Try putting in the following line of code at the prompt (it's a little
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clearer what it does if the prompt is several lines down the terminal when
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you put this in): <code>echo -en "\033[7A\033[1;35m BASH \033[7B\033[6D"</code>
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This should move the cursor seven lines up screen, print the word " BASH ",
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and then return to where it started to produce a normal prompt. This isn't
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a prompt: it's just a demonstration of moving the cursor on screen, using
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colour to emphasize what has been done.
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</p><p><font face="Helvetica">Save this in a file called "clock":
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<pre><font face="Helvetica">#!/bin/bash
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function prompt_command {
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let prompt_x=$COLUMNS-5
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PROMPT_COMMAND=prompt_command
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local BLUE="\[\033[0;34m\]"
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local RED="\[\033[0;31m\]"
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local LIGHT_RED="\[\033[1;31m\]"
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local WHITE="\[\033[1;37m\]"
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local NO_COLOUR="\[\033[0m\]"
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TITLEBAR='\[\033]0;\u@\h:\w\007\]'
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\[\033[s\033[1;\$(echo -n \${prompt_x})H\]\
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$BLUE[$LIGHT_RED\$(date +%H%M)$BLUE]\[\033[u\033[1A\]
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$BLUE[$LIGHT_RED\u@\h:\w$BLUE]\
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</p><p><font face="Helvetica">This prompt is fairly plain, except that it keeps a 24 hour clock in the
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upper right corner of the terminal (even if the terminal is resized). This
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will NOT work on the terminal emulators that I mentioned that don't accept
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the save and restore cursor position codes. If you try to run this prompt
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in any of those terminal emulators, the clock will appear correctly, but
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the prompt will be trapped on the second line of the terminal.
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</p><p><font face="Helvetica">See also
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<a href="http://new.linuxnow.com/docs/content/Bash-Prompt-HOWTO-html/Bash-Prompt-HOWTO-12.html#clock3">The Elegant Useless Clock Prompt</a> for a
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more extensive use of these codes.
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</p><h2><font face="Helvetica"><a name="ss6.3">6.3 Moving the Cursor With tput</a>
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<p><font face="Helvetica">As with so many things in Unix, there is more than one way to achieve the
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same ends. A utility called "tput" can also be used to move the cursor
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around the screen, or get back information about the status of the
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terminal. "tput" for cursor positioning is less flexible than ANSI escape
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sequences: you can only move the cursor to an absolute position, you can't
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move it relative to its current position. I don't use "tput," so I'm not
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going to explain it in detail. Type "man tput" and you'll know as much as
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