Colorized bash prompt overwrites previous command’s output if the output doesn’t end with a newline

bashcolorscommand lineprompt

On my system, when using a colorized prompt, the last line of the previous command's output gets overwritten if the last character of the output isn't a newline.

Ex:
Using the default, non-colored bash prompt, we have:

[myusername@myhostname dirname]$ echo -n foo-bar
foo-bar[myusername@myhostname dirname]$

This is expected.

However, using the following colorized prompt:

PS1='\[\033[1;32m\]\u@\h\[\033[0m\]:\[\033[1;34m\]\w\[\033[0m\]\$ '

we have (shown here without the color):

myusername@myhostname:~/path/to/dirname$ echo -n foo-bar
myusername@myhostname:~/path/to/dirname$ rname$

The cursor is now located on the last "r" in the line. Typing some characters at the prompt overwrites the last "rname$". The end result is that if the previous command's output does not end in a newline, I cannot see what it is. This is the most important thing to fix. The way the extra characters appear, but are over writeable, doesn't bother me much, but would also be nice to fix.

I've tried this with other colorized prompts from bash documentation, and some colored prompts from other super user answers regarding colorized prompts, and they all behave the exact same way.

$ bash --version
GNU bash, version 3.1.17(1)-release (x86_64-redhat-linux-gnu)
Copyright (C) 2005 Free Software Foundation, Inc.

Not sure, but I think it's CentOS, don't know what version. Give me a command to check the O.S., and I'll run it.

Best Answer

My preferred solution is simply to have the prompt always begin with a newline. That way I always have a blank line between the last command output (except in this case, of course), which feels more natural to me. And the worst case is that instead of overwriting text like you are seeing, I don't get the blank line in between. Unless you try it out for a while and simply can't stand the blank line, I highly recommend it.

PS1='\n\[\033[1;32m\]\u@\h\[\033[0m\]:\[\033[1;34m\]\w\[\033[0m\]\$ '

An additional suggestion, if you're up for it: I also use a multi-line prompt to make my command line as long as possible before wrapping (or scrolling if your terminal or shell is configured for that). I also like to know the history line number. Those two together:

PS1='\n\[\033[1;32m\]\u@\h\[\033[0m\]:\[\033[1;34m\]\w\[\033[0m \!\]\n\$ '

Finally, I also like to get timestamps printed before and after running commands. A simplified version of what I use for that is:

export PROMPT_COMMAND="date +\"%Y-%m-%d %H:%M:%S (%s)\"; trap 'date +\"%Y-%m-%d %H:%M:%S (%s)\"; trap DEBUG' DEBUG"

Head spinning yet? :)

Related Solutions

Is there a command to get bash to print a new prompt string and redraw the current line

Use redraw-current-line function of bind builtin. First check if it's already bound maybe:

bind -q redraw-current-line

I've never seen it bound by default, so you will probably need to bind it. Pick a key combination, let's say Ctrl+Y. Check if it's already taken:

bind -p | grep -F '"\C-y'

Empty output means the combination is unused. If so, let's bind redraw-current-line to it:

bind "\C-y":redraw-current-line

Now, whenever a background process messes with your command line, hit Ctrl+Y. Then your prompt will be redrawn along with whatever command you have just partially typed (if any), so you can continue as if nothing happened.

To make the binding permanent you could add the above command to your ~/.bashrc, but don't. The right approach is to modify ~/.inputrc (for user) or /etc/inputrc (system-wide). This way any program that uses readline(3) library will obey. The line to add to either file looks like this:

"\C-y":redraw-current-line

But if you create ~/.inputrc anew, make sure its first line says $include /etc/inputrc. This is because up to this point readline has used /etc/inputrc and maybe your workflow relies on what's in this file. From now on, the library will use your ~/.inputrc instead; the line $include /etc/inputrc makes it parse the system-wide file as well.

For more info see help bind and man 3 readline.

Move vi mode string to end of bash prompt

You can achieve that by setting a very long mode string for cmd and insert modes, that include the other items you want in your prompt. Note that this means you won't be able to use special shortcuts available in PS1, such as \w for a "pretty" printing of your current directory. But you can probably achieve the same in shell code that does the same.

You can set the readline variables using the bind "set vi-ins-mode-string \"...\"" and bind "set vi-cmd-mode-string \"...\"" commands. (see help bind for more details.) And you can set that from your PROMPT_COMMAND, so that it will get reset before each prompt (so it will reflect change of directory, date and time if you include them, etc.)

Quoting can get tricky :-)

For the example you used yourself:

/current/dir/here $ i:

You could use this:

reset_readline_prompt_mode_strings () {
    bind "set vi-ins-mode-string \"$PWD \$ \1\e[1;32m\2i:\1\e[0m\2\""
    bind "set vi-cmd-mode-string \"$PWD \$ \1\e[1;31m\2c?\1\e[0m\2\""
}
PROMPT_COMMAND=reset_readline_prompt_mode_strings
PS1=' '

Like mentioned, the expansion of $PWD will include the full path and won't use relative paths from ~, etc.

You can get the same expansion used in prompts by using bash's ${variable@P} operator expansion:

EMBEDDED_PS1='\w $ '
reset_readline_prompt_mode_strings () {
    bind "set vi-ins-mode-string \"${EMBEDDED_PS1@P}\1\e[1;32m\2i:\1\e[0m\2\""
    bind "set vi-cmd-mode-string \"${EMBEDDED_PS1@P}\1\e[1;31m\2c?\1\e[0m\2\""
}

Please note that you need PS1 to be set to something non-empty, otherwise no prompt is printed at all. You can use a single space in this case. You might want to consider setting PS2 appropriately, for line continuations.

BTW, my recommendation for symbols and colors for the ins and cmd mode strings are:

cmd should use : (same as you can type : commands from normal mode in Vim) and should use a green color (since that's the default color set by lightline in the status line for "Normal" mode.)
ins should use + (which is the symbol used by Vim to show a buffer is modified, when you insert, you modify it) and should use a blue color (default color used by lightline in the status line for "Insert" mode.)

Personally, I think these below are pretty cool:

EMBEDDED_PS1='\w $ '
reset_readline_prompt_mode_strings () {
    bind "set vi-ins-mode-string \"${EMBEDDED_PS1@P}\1\e[32m\2: >\1\e[92m\2>\1\e[0m\2>\""
    bind "set vi-cmd-mode-string \"${EMBEDDED_PS1@P}\1\e[34m\2+ >\1\e[94m\2>\1\e[0m\2>\""
}
PROMPT_COMMAND=reset_readline_prompt_mode_strings
PS1=' '
PS2=' ... '

Best Answer

Related Solutions

Is there a command to get bash to print a new prompt string and redraw the current line

Move vi mode string to end of bash prompt

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