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why bash completion sometimes doesn't work?

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  why bash completion sometimes doesn't work? Long Wind <longwind2@yahoo.com> - 2022-01-03 06:30 +0100
    Re: why bash completion sometimes doesn't work? Greg Wooledge <greg@wooledge.org> - 2022-01-03 13:30 +0100
      Re: why bash completion sometimes doesn't work? Richmond <richmond@criptext.com> - 2022-01-03 15:50 +0100
      Re: why bash completion sometimes doesn't work? Long Wind <longwind2@yahoo.com> - 2022-01-03 21:20 +0100
        Re: why bash completion sometimes doesn't work? Greg Wooledge <greg@wooledge.org> - 2022-01-03 21:30 +0100
        Re: why bash completion sometimes doesn't work? David Wright <deblis@lionunicorn.co.uk> - 2022-01-03 22:50 +0100
          Re: why bash completion sometimes doesn't work? Long Wind <longwind2@yahoo.com> - 2022-01-04 01:00 +0100
            Re: why bash completion sometimes doesn't work? Greg Wooledge <greg@wooledge.org> - 2022-01-04 03:30 +0100
              Re: why bash completion sometimes doesn't work? Long Wind <longwind2@yahoo.com> - 2022-01-04 03:50 +0100
                Re: why bash completion sometimes doesn't work? Greg Wooledge <greg@wooledge.org> - 2022-01-04 04:00 +0100
              Re: why bash completion sometimes doesn't work? David Wright <deblis@lionunicorn.co.uk> - 2022-01-04 20:40 +0100

#243618 — why bash completion sometimes doesn't work?

when i type "ifdown wl" and press Tab, it shall complete it with full device name wlx12345
i believe it's taken from /etc/network/interfaces
but sometimes it doesn't work in buster

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#243628

On Mon, Jan 03, 2022 at 05:25:31AM +0000, Long Wind wrote:
> when i type "ifdown wl" and press Tab, it shall complete it with full device name wlx12345
> i believe it's taken from /etc/network/interfaces
> but sometimes it doesn't work in buster

You're describing "programmable completion", which is an optional
feature of bash.  It's done on a per-command basis.  E.g. if you
type "cd wlx<TAB>" it will not complete the wlx word using interface
names, because there is no such completion defined for the "cd" command.
Apparently there is (on your system) for "ifdown" though.

By default, Debian installs the bash-completion package, which contains
programmable completions for a whole bunch of commands.  This is
enabled by dotting in a file from ~/.bashrc (the code to do this is
at the end of /etc/skel/.bashrc, which becomes the default user ~/.bashrc
file if you add users with "adduser").

Unless told otherwise, we're going to assume you're using bash (not zsh)
as your shell, and that you've got the standard Debian ~/.bashrc file,
so that bash's programmable completion has been enabled.

If some programmable completion isn't working the way you expect, then
you need to gather some more information.  Give us the versions of
the bash and bash-completion packages that you've got installed, and
then tell us the EXACT command you typed, and what results you got by
pressing Tab.

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#243630

Greg Wooledge <greg@wooledge.org> writes:

> By default, Debian installs the bash-completion package, which contains
> programmable completions for a whole bunch of commands.  This is
> enabled by dotting in a file from ~/.bashrc (the code to do this is
> at the end of /etc/skel/.bashrc, which becomes the default user ~/.bashrc
> file if you add users with "adduser").
>

Reading this has solved something which has puzzled me for some time. My
.bashrc is a leftover from when I was running Opensuse, and so bash
completion has never quite worked properly on the su command. Now I have
copied /etc/skel/.bashrc and it is working!

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#243638

Thank Greg!  i use bash 5.0-4 and bash-completion 1:2.8-6
all bash setting for root is default except 3 alias 

 alias rm='rm -i'
 alias cp='cp -i'
 alias mv='mv -i'

i type "ifdown wl" and press Tab, nothing happens
there's only one wireless device in /etc/network/interfaces
it shall complete command to "ifdown wlx12345" 

i've read /etc/skel/.bashrc, programmable completion seems enabled by default
and it works for other commands, e.g. i type "dhclient enp" and Tab, it becomes "dhclient enp0s1" 

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#243639

On Mon, Jan 03, 2022 at 08:12:50PM +0000, Long Wind wrote:
> Thank Greg!  i use bash 5.0-4 and bash-completion 1:2.8-6

> i type "ifdown wl" and press Tab, nothing happens
> there's only one wireless device in /etc/network/interfaces
> it shall complete command to "ifdown wlx12345" 
> 
> i've read /etc/skel/.bashrc, programmable completion seems enabled by default
> and it works for other commands, e.g. i type "dhclient enp" and Tab, it becomes "dhclient enp0s1" 

Well.  In this package, the completions for ifdown and dhclient
are very different.  E.g. in dhclient's completion, there's code that
looks like this:

    if [[ "$cur" == -* ]]; then
        COMPREPLY=( $( compgen -W '-p -d -q -1 -r -lf -pf -cf -sf -s -g -n -nw
            -w' -- "$cur" ) )
    else
        _available_interfaces

The ifdown completion, on the other hand, has:

    if [[ $cword -eq 1 ]]; then
        _configured_interfaces
        COMPREPLY=( $(compgen -W '${COMPREPLY[@]}' -- "$cur") )

I wonder what the difference between _available_interfaces and
_configured_interfaces is.  Looks important.

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#243642

On Mon 03 Jan 2022 at 20:12:50 (+0000), Long Wind wrote:
> Thank Greg!  i use bash 5.0-4 and bash-completion 1:2.8-6
> all bash setting for root is default except 3 alias 
> 
>  alias rm='rm -i'
>  alias cp='cp -i'
>  alias mv='mv -i'
> 
> i type "ifdown wl" and press Tab, nothing happens
> there's only one wireless device in /etc/network/interfaces
> it shall complete command to "ifdown wlx12345" 
> 
> i've read /etc/skel/.bashrc, programmable completion seems enabled by default
> and it works for other commands, e.g. i type "dhclient enp" and Tab, it becomes "dhclient enp0s1"

Type:

  ifdown <TAB><TAB>

and you should get a list that will contain at least "lo".

Cancel that line and type:

  ip a

to see what interfaces you actually have.

Cheers,
David.

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#243660

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

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#243665

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.

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.

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#243667

Thank Greg Wooledge!

it seems solved, 
there's more whitespace between iface and device name, 
i correct it to just one space, and bash completion works for ifup/ifdown

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#243669

On Tue, Jan 04, 2022 at 02:39:24AM +0000, Long Wind wrote:
> 
> Thank Greg Wooledge!
> 
> it seems solved, 
> there's more whitespace between iface and device name, 
> i correct it to just one space, and bash completion works for ifup/ifdown

Might be worth a bug report.

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#243696

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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