How to reset COMP_WORDBREAKS without affecting other completion script?

Question

There is something confuse me when I implement a bash auto-completion function which I'll put it in /etc/bash_completion.d/

In order to achieve some feature, I want to remove the word break characters colon (:) from variable $COMP_WORDBREAKS and add a slash (/) at begin of $COMP_WORDBREAKS.

COMP_WORDBREAKS=" /'><=;|&("
_mytool()
{
    local cur=${COMP_WORDS[COMP_CWORD]}
    compopt -o nospace

    # my implement here

    COMPREPLY=( $(compgen ..........my_implement......... -- $cur) )
}
complete -F _mytool mytool

However, I can't reset COMP_WORDBREAKS directly because the value is shared with other completion scripts. By the time the completion function gets called, variable COMP_WORDS array has already been populated, so locally changes COMP_WORDBREAKS have no effect.

Is there any solution for changing COMP_WORDBREAKS in one completion script and no effect to other script?

$ echo $BASH_VERSION
4.2.10(1)-release

Answer 1

Modifying $COMP_WORDBREAKS in your completion script is not the recommended way (as it is a global variable and it could affect the behavior of other completion scripts - for example ssh).

However, bash completion offers some helper methods which you can use to achieve your goal.

The recommended way to handle non-word-breaking characters in completion words is by using the two helper methods:

• _get_comp_words_by_ref with the -n EXCLUDE option
  
  • gets the word-to-complete without considering the characters in EXCLUDE as word breaks
• __ltrim_colon_completions
  • removes colon containing prefix from COMPREPLY items
    (a workaround for http://tiswww.case.edu/php/chet/bash/FAQ - E13)

So, here is a basic example of how to a handle a colon (:) in completion words:

_mytool()
{
    local cur
    _get_comp_words_by_ref -n : cur

    # my implementation here

    COMPREPLY=( $(compgen ..........my_implement......... -- $cur) )

    __ltrim_colon_completions "$cur"
}
complete -F _mytool mytool

As a final tip, the helper methods are located in /etc/bash_completion. Take a look inside to read a detailed description of each method and to discover more helper methods.