Re-escape brackets in PS1

Question

As others have pointed out, color codes in PS1 should be bracketed by \[ and \] to avoid them taking up horizontal space. I've added the necessary code to .bashrc:

highlight()
{
    if [ -x /usr/bin/tput ]
    then
        printf '\['
        tput bold
        printf '\]'
        printf '\['
        tput setaf $1
        printf '\]'
    fi
    shift
    printf -- "$@"
    if [ -x /usr/bin/tput ]
    then
        printf '\['
        tput sgr0
        printf '\]'
    fi
}

highlight_error()
{
    highlight 1 "$@"
}

The last function is used in PS1 in both normal and escaped command substitutions to be able to change the string based on the result of the previous command:

# Exit code
PS1="\$(exit_code=\${?#0}
highlight_error \"\${exit_code}\${exit_code:+ }\")"

...

if [ "$USER" == 'root' ]
then
    PS1="${PS1}$(highlight_error '\u')"
else
    PS1="${PS1}\u"
fi

The issue is then that the escaped brackets are output as literals, so my prompt looks like this after running a command which doesn't exist:

\[\]\[\]127 \[\]user@machine:/path
$

Wrapping the escaped highlight_error in printf %b didn't help. How can I fix the output so that I can use the functions for both normal and escaped command substitutions?

Answer 1

It seems that any escape sequence actually in PS1 literally needs to be wrapped in \[ and \], but if you call a function or command that produces output, it does not need to be wrapped.

So why not just move the

"\$(exit_code=\${?#0}
highlight_error \"\${exit_code}\${exit_code:+ }\")"

stuff inside a function, e.g.

print_error_if_error()
{
    exit_code=$?
    if [ $exit_code -ne 0 ]; then
        highlight_error "$exit_code "
    fi
}

and then I think you can remove all the \[ and \] stuff...

highlight()
{
    if [ -x /usr/bin/tput ]
    then
        tput bold
        tput setaf $1
    fi
    shift
    printf -- "$@"
    if [ -x /usr/bin/tput ]
    then
        tput sgr0
    fi
}

highlight_error()
{
    highlight 1 "$@"
}

PS1='$(print_error_if_error)'

# ...

if [ "$USER" = 'root' ]
then
    PS1="${PS1}$(highlight_error '\u')"
else
    PS1="${PS1}\u"
fi