Bash doesn’t calculate prompt length correctly

bashprompt

I've googled around quite a bit on this problem and found a few related problems, like this one: Terminal prompt not wrapping correctly.

My problem is that bash doesn't calculate the length of the prompt correctly, which messes it up when I do things like ctrl–r or ↑ to scroll through history. This is basically how it should look (without colors).

✔ name@machine ~

01:09 $

When I for example scroll through previous commands with up-arrow, some character gets stuck in the prompt:

✔ name@machine ~

01:09 $m

Sometimes I also get other weird behaviour, like some of the prompt being overwritten (it all goes away when I reload it). My prompt looks like this:

GIT_PROMPT_START_USER="\n_LAST_COMMAND_INDICATOR_ \[$Magenta\]\u\[$Orange\]@\[$White\]\h \[$Yellow\]\[$PathShort\]\[$ResetColor\]"

GIT_PROMPT_END_USER="\n\[$Blue\]$Time12a\[$ResetColor\] $ "

I use something called git-bash-prompt: >https://github.com/magicmonty/bash-git-prompt>.

I think what is messing it up is the time variable, which is defined in another file:

Time12a="\$(date +%H:%M)"

I've tried both \[$Time12a\] and $Time12a in GIT_PROMPT_END_USER, but none of them seem to work. My guess is that bash calculates it wrong because $Time12a represents 5 characters (hh:mm).

How does bash calculate the length of this? Is it possible to explicitly set the length for bash? Answers very appreciated!

Best Answer

So I found out what messed it up, and it was not what I expected :)

It was actually the \[$ResetColor\] that bash for some reason used to count the length forward one step (bash thought my prompt was 1 step longer).

The variable was defined by "bash-git-prompt" along with all the other colors (see the link to the git-repo in the question if you want to look into it). Anyways, the fix was easy. I just overrode their definition with my own:

ResetColor=$(tput sgr0)

Fixed!

(Just btw if somebody else is also having this problem, I have already overridden all the other colors I used with my own definitions using $COLOR=$(tput setaf X) where COLOR is the color you want and X is that color's xterm-256 number.)

Related Solutions

Terminal Prompt Issues – Fixing Prompt Not Wrapping Correctly

Non-printable sequences should be enclosed in \[ and \]. Looking at your PS1 it has a unenclosed sequence after \W. But, the second entry is redundant as well as it repeats the previous statement "1;34".

\[\033[01;32m\]\u:\[\033[01;34m\] \W\033[01;34m \$\[\033[00m\]
                  |_____________|               |_|
                         |                       |
                         +--- Let this apply to this as well.

As such this should have intended coloring:

\[\033[1;32m\]\u:\[\033[1;34m\] \W \$\[\033[0m\]
                               |_____|
                                  |
                                  +---- Bold blue.

Keeping the "original" this should also work:

\[\033[1;32m\]\u:\[\033[1;34m\] \W\[\033[1;34m\] \$\[\033[0m\]
                                  |_|         |_|
                                   |           |
                                   +-----------+-- Enclose in \[ \]

Edit:

The reason for the behavior is because bash believes the prompt is longer then it actually is. As a simple example, if one use:

PS1="\033[0;34m$"
       1 2345678

The prompt is believed to be 8 characters and not 1. As such if terminal window is 20 columns, after typing 12 characters, it is believed to be 20 and wraps around. This is also evident if one then try to do backspace or Ctrl+u. It stops at column 9.

However it also does not start new line unless one are on last column, as a result the first line is overwritten.

If one keep typing the line should wrap to next line after 32 characters.

Problem with 256-bit Color Codes in Bash Prompt – Fix Guide

This line

PS1+="\$(prompt_git \"${blue}\")"; # Git repository details

does not have the \[ and \] markers used by bash to tell it to not count columns for each character enclosed. If not told otherwise, it assumes that printable characters should be counted.

For discussion:

3.4. Non-Printing Characters in Prompts (Bash Prompt HOWTO)
Changing Colors (xterm manual)

Best Answer

Related Solutions

Terminal Prompt Issues – Fixing Prompt Not Wrapping Correctly

Edit:

Problem with 256-bit Color Codes in Bash Prompt – Fix Guide

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