[Bash-completion-devel] [RFC] support 'COMP_WORDBREAKS' value on a per-completion basis

Raphaël raphael.droz at gmail.com
Fri May 27 14:03:16 UTC 2011

=== Rational:
Let's say you want to complete http URL (which contain ':').

You'll probably use this kind of expression:

_comp() {
	COMPREPLY=( $(compgen -W "http://foo http://bar" -- "$cur") )

After the completion function is evaluated, readline will consider
the value of $COMP_WORDBREAKS to split the word to complete...
If the current argument is 'http://'
- if $COMP_WORDBREAKS contains ':' , only '//' will be used by the
completion process.
- otherwise (and if ' ' (space) is part of $COMP_WORDBREAKS), the
whole 'http://' string will be used.

The problem is that this evaluation happens after the completion script
returns (and won't work before $COMP_WORDBREAKS has been modified to
match our needs):

The FAQ says:
E13) Why does filename completion misbehave if a colon appears in the filename?

_comp() {
	COMPREPLY=( $(compgen -W "http://foo http://bar" -- "$cur") )

it has mainly two drawbacks:

1) the completion has to alter the user environment
 $ comp http://<TAB>
"'><=;|&(       ### ':' has disappeared, other completion functions
		### may suffer from this

2) the first time we try a completion, _comp() has not yet been executed
so our modified $COMP_WORDBREAKS isn't yet part of the context.
 $ comp http://<TAB>
completes (the first time) to
 $ comp http:http://
but after that, $COMP_WORDBREAKS is modified and the next calls will succeed.

=== the proposed patch is in 3 parts (also attached):

Adds a char *word_breaks to the COMPSPEC struct

Support of a -B <COMP_WORDBREAKS> flag to the complete builtin

registers readline 'rl_completion_word_break_hook' and makes the bash
function returns the value of the complete -B <flag> if it was
specified during the call to the 'complete' builtin.

If the rationale of this patch is accepted, I would be happy to discuss
the possibility to have it implemented at the 'compopt' level (what I
was unable to do) in order to change dynamically word bounds *during* the
completion process.

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