Why does this bash prompt sometimes keep part of previous commands when scrolling history?

Question

My bash prompt, which I'll admit to have stolen from a few places and cobbled together, will sometimes add part of previous commands to its length when scrolling the bash history with up/down arrows.

For example, if my previous commands were:

ls
cd /home/caleb
vim .bashrc

When I was at my prompt and scrolled up twice it might look like:

$ vim .bcd /home/caleb

Where the first five characters are left over from last command.

Does anyone have any idea why this is happening, and how it can be stopped?

My prompt is set with this code (way to long to include here): https://gist.github.com/1679352

Answer 1

Somewhere your prompt is fubar. What usually happens is that your shell thinks its outputting non-printable term codes and expecting it to take up space. The best advice I can give you is to systematically add to (or take away from) your prompt until this behavior stops to isolate the code that is causing this issue.

Answer 2

The color codes need to be wrapped in square brackets. The brackets inform bash that the enclosed text should not be printed

building on @Phreditor's example, this shows that any formatting done after the newline will result in the original issue:

export PS1="\n\n\[\033[01;33m[\w]\033[00m\n\033[0;90m\$ "

wrapping the format code in [] ensures that annoying behavior never happens:

export PS1="\n\[\[\033[01;33m\][\w]\[\033[00m\]\n\[\033[0;90m\]\$ "

The documentation: http://tldp.org/HOWTO/Bash-Prompt-HOWTO/nonprintingchars.html

Since PS1 formatting causes the value to be so long and hard to read I put the format codes in variables:

BYELLOW='\[\033[01;33m\]'
IBLACK='\[\033[0;90m\]'
PS_CLEAR='\[\033[0m\]'
export PS1="\n${BYELLOW}[\w]${PS_CLEAR}\n${IBLACK}\$ "

Answer 3

I had the same problem and it was related to the color definitions.

In my case, I have a multi-line prompt (gives most space for current command regardless of path length displayed by prompt).

Bad version:

export PS1="\n\n\[\033[01;33m[\w]\n\033[00m\$ "

Good version:

export PS1="\n\n\[\033[01;33m[\w]\033[00m\n\$ "

\033[00m terminates the color. If it is after the new line (\n), it prevents proper redraw in the terminal, to overwrite previous commands with background color. Moving it behind the new line resolved the problem.

(using Terminal in Mac OS 10.8)

Answer 4

I actually think this has to do with a missing 'non-printing character' delimiter. I had exactly the same issue, but moving it before the newline (\n) didn't fix it. Instead I correctly surrounded all non-printing characters (here, colouring commands) with '\[' and '\]'.

Bad (works, but has the history-mashing problem described above):

PS1="\e[32m\u\e[35m@\e[32m\h \e[33m\w\e[36m\n\$\e[0m"

Good (surrounded all colour commands with '\[' and '\]' - does not show mashed command history):

PS1="\[\e[32m\]\u\[\e[35m\]@\[\e[32m\]\h \[\e[33m\]\w\[\e[36m\]\n\$\[\e[0m\]"

i.e. "\e[...m" --becomes--> "\[\e[...m\]"

And if you are putting this into something like SecureCRT to auto-send upon login to a system, you may have to double escape everything (put double backslashes everywhere) if auto-login system consumes the first backslash itself to determine the character to be sent:

PS1="\\[\\e[32m\\]\\u\\[\\e[35m\\]@\\[\\e[32m\\]\\h \\[\\e[33m\\]\\w\\[\\e[36m\\]\\n\\$\\[\\e[0m\\]"

i.e. "\..." --becomes--> "\\..."

(This is definitely true of SecureCRT and may be true of others, such as PuTTY or TeraTerm - testing required on your part.)