Ubuntu – PS1 problem, messing up CLI

bashcommand lineps1

I did a simple PS1 assignment

PS1="\e[0;31m[\W]\$ \e[m "

All I wanted to do was to change the prompt color and display only the relative path. However this messes up the CLI. For example, when browsing history with the ↑ it crops and overlaps the display. When i type a long command the cursor moves to the beginning of the screen overlapping with the prompt display itself. What have I done wrong?

Best Answer

That's because bash thinks the prompt is longer than it is. The escape sequence \e[0;31m for instance, gets sucked up by the terminal, which in turn turns the following text red, but bash doesn't know that. So, you have to tell bash that that sequence of characters should not be counted in the prompt's length, and you do that by enclosing it in \[ \]. I also recommend using tput instead of hardcoding terminal escape sequences.

red=$(tput setaf 1)
reset=$(tput sgr0)
PS1='\[$red\][\W]\$\[$reset\] '

See BashFAQ 53 and Terminal codes (ANSI/VT100) introduction for more.

References

So far, there hasn't been a single reference for everything that can go in a Bash prompt - but as it's a feature that has evolved over decades and probably varies from distro to distro, maybe that's too much to ask. I've tried to summarise what I found most useful here.

This how-to is the most complete, but is very long and rambling. Some of the more useful sections:

Section 2.4 and 2.5 explain the basics of setting PS1, including the (printable) escape characters.
Section 3.4 explains why \[ and \] are necessary.
Section 6 explains all the main (non-printable) escape sequences you might want to use, including setting the colour of the prompt and the title of an xterm window.

This guide explains how ${} works in Bash in general, and this Ask Ubuntu question explains a bit more about how that works with debian_chroot.

Between those, I think every character in the default Ubuntu PS1 variable is explained.

Explanation of the Ubuntu prompt

There are three parts to the prompt:

\[\e]0;\u@\h: \w\a\] sets the title bar of an xterm window:
- \[ starts a section of non-printable characters
- \e]0; is the escape sequence for 'set xterm title' (I believe numbers other than 0 will set other xterm properties, though I haven't tested this)
- \u@\h: \w the title to use (see below for \u, \h and \w)
- \a marks the end of the title
- \] marks the end of non-printable characters
${debian_chroot:+($debian_chroot)} expands to the value of $debian_chroot in parentheses if $debian_chroot is set. See this question for more information about $debian_chroot.
\u@\h:\w\$ is the prompt itself:
- \u expands to the current username
- \h expands to the current hostname
- \w expands to the current working directory
- \$ expands to # for root and $ for all other users

Ubuntu – .bashrc edit messes up terminal command arrow-up history print

I have no idea why (never really understood the escape codes), but adapting the other prompt seems to work:

PS1='\[\033[1;32m\][\W]\$ \[\033[00m\]'

Apparently, you need to enclose the escape sequences in \[...\], to tell bash not to count them while determining the prompt width. Therefore, both the above PS1 and the following would work equally well:

PS1='\[\e[1;32m\][\W]\$ \[\e[m\]'

Best Answer

Related Solutions

Ubuntu – find a complete reference for the $PS1 variable

References

Explanation of the Ubuntu prompt

Ubuntu – .bashrc edit messes up terminal command arrow-up history print

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