Re: why bash completion sometimes doesn't work?
On Mon 03 Jan 2022 at 21:22:44 (-0500), Greg Wooledge wrote:
> On Mon, Jan 03, 2022 at 11:56:57PM +0000, Long Wind wrote:
> > Thank Greg and David!
> >
> > i type "ifdown <TAB><TAB>", it add lo automatically,
> > wireless device isn't shown, though wireless connection works well
> >
> > i think "ip a" can list wireless device
>
> Well, it sounds like _configured_interfaces on your system only finds
> "lo", whereas _available_interfaces finds a larger set.
>
> _configured_interfaces is apparently defined in
> /usr/share/bash-completion/bash_completion and includes this code:
>
> if [[ -f /etc/debian_version ]]; then
> # Debian system
> COMPREPLY=($(compgen -W "$(command sed -ne 's|^iface \([^ ]\{1,\}\).*$|\
> 1|p' \
> /etc/network/interfaces /etc/network/interfaces.d/* 2>/dev/null)" \
> -- "$cur"))
>
> If I'm reading that sed command correctly, it only works if there is
> precisely ONE space between "iface" and the interface name.
>
> Perhaps your iface lines in /etc/network/interfaces are using tabs, or
> more than one space, between the word "iface" and the interface name.
> If so, that's why this particular bash-completion function doesn't
> return it.
>
> It's also possible that your desired interfaces aren't defined in
> /etc/network/interfaces at all. You might be using Network-Manager
> instead, on that system. That's perfectly valid, but this bash-completion
> function won't see those interfaces.
There's another assumption in that pattern: that /e/n/i contains
source /etc/network/interfaces.d/*
That line could be absent, pointing somewhere else, or it could
be the subtly different source-directory keyword that filters
the filenames in the directories to a particular charset.
> The _available_interfaces function (used by dhclient's completion function)
> is very different. It calls "ifconfig -a" or "ip link show" and then
> parses names out with awk. Or at least it tries to. Obviously that will
> give different results, if your interfaces are defined by Network-Manager,
> or systemd units, or if you used liberal whitespace, etc.
>
> Have I mentioned yet that bash-completion has some notoriety for being
> fragile and a bit broken at times? I don't use it personally. If it
> works for you, that's great. But it's far from perfect.
Cheers,
David.
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