219 lines
3.8 KiB
HTML
219 lines
3.8 KiB
HTML
<HTML
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>Non-Printing Characters in Prompts</TITLE
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>Bash Prompt HOWTO: </TH
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>Chapter 3. Bash Programming and Shell Scripts</TD
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><A
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NAME="NONPRINTINGCHARS"
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></A
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>3.4. Non-Printing Characters in Prompts</H1
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><P
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>Many of the changes that can be made to Bash prompts that are discussed in
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this HOWTO use non-printing characters. Changing the colour of the prompt
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text, changing an Xterm title bar, and moving the cursor position all
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require non-printing characters. </P
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><P
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>If I want a very simple prompt consisting of a greater-than sign and a
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space: </P
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><TABLE
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BORDER="1"
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BGCOLOR="#E0E0E0"
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><PRE
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>[giles@nikola giles]$ PS1='> '
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> </PRE
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></FONT
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></TD
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></TR
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></TABLE
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><P
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>This is just a two character prompt. If I modify it so that it's a
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bright yellow greater-than sign (colours are discussed in their own
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section): </P
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><TABLE
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BORDER="1"
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BGCOLOR="#E0E0E0"
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WIDTH="100%"
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><TR
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><TD
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><FONT
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COLOR="#000000"
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><PRE
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CLASS="SCREEN"
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>> PS1='\033[1;33m>\033[0m '
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> </PRE
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></FONT
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></TD
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></TR
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></TABLE
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><P
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>This works fine - until you type in a large command line. Because the
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prompt still only consists of two printing characters (a greater-than sign
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and a space) but the shell thinks that this prompt is eleven characters
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long (I think it counts '\033' , '[1' and '[0' as one character each). You
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can see this by typing a really long command line - you will find that the
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shell wraps the text before it gets to the edge of the terminal, and in
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most cases wraps it badly. This is because it's confused about the actual
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length of the prompt. </P
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><P
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>So use this instead: </P
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><TABLE
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WIDTH="100%"
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><TD
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><FONT
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COLOR="#000000"
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><PRE
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CLASS="SCREEN"
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>> PS1='\[\033[1;33m\]>\[\033[0m\] '</PRE
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></FONT
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></TD
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></TR
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></TABLE
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><P
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>This is more complex, but it works. Command lines wrap properly. What's
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been done is to enclose the '\033[1;33m' that starts the yellow colour in
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'\[' and '\]' which tells the shell "everything between these escaped
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square brackets, including the brackets themselves, is a non-printing
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character." The same is done with the '\033[0m' that ends the colour. </P
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