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Bug#708979: closed by Gioele Barabucci <gioele@svario.it> (Re: Bug#708979: bash (readline): Something is wrong with binding keys to functions)

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On 2024-08-13 16:28:42 +0100, Reuben Thomas wrote:
> I'm not quite sure I understand you here: are you saying that it's
> documented somewhere that one should use the "\e" form?

I'm saying that since the documentation says that the Meta key
may generate an Escape character (which is actually the case in
general), you should use the \e form as a consequence.

I think that knowing how things work exactly is complex due to
the various variables. From the readline(3readline) man page,
in particular:

  convert-meta (On)
    If  set  to  On, readline will convert characters with the eighth
    bit set to an ASCII key sequence by stripping the eighth bit  and
    prefixing it with an escape character (in effect, using escape as
    the meta prefix).  The default is On, but readline will set it to
    Off  if  the locale contains eight-bit characters.  This variable
    is dependent on the LC_CTYPE locale category, and may  change  if
    the locale is changed.

  enable-meta-key (On)
    When set to On, readline will try to enable any meta modifier key
    the terminal claims to support when it is called.  On many termi‐
    nals, the meta key is used to send eight-bit characters.

(Note: This is wrong, nowadays, the Meta key generates an Escape
character.)

  input-meta (Off)
    If set to On, readline will enable eight-bit input (that  is,  it
    will  not  clear  the eighth bit in the characters it reads), re‐
    gardless of what the terminal claims it can  support.   The  name
    meta-flag  is  a  synonym for this variable.  The default is Off,
    but readline will set it to On if the locale  contains  eight-bit
    characters.   This  variable  is dependent on the LC_CTYPE locale
    category, and may change if the locale is changed.

> As I said in my original report, "\M-" worked fine in readline 5.0.
> So as far as I can tell, it's a regression.

Indeed, you said:

"With readline 5.0 they work fine, but with 5.1 they don't work."

In the CHANGES file:

------------------------------------------------------------------------
This document details the changes between this version, readline-5.1,
and the previous version, readline-5.0.
[...]
m.  Fixed a bug that caused "\M-x" style key bindings to not obey the setting
    of the `convert-meta' variable.
------------------------------------------------------------------------

So you can get the previous behavior about the .inputrc file with

  set convert-meta On

but this means that non-ASCII characters (i.e. with the 8th bit set)
will be regarded as ASCII characters with the Meta key.

> In any case, I can't see any sense in requiring \e for some keys and
> not others.

I suppose that this was historical. IMHO, any behavior based on the
8th bit should be removed. Nowadays, the 8th bit should be used for
non-ASCII characters, not to provide meta key information. This
would mean that "\M-" in the .inputrc file should behave like "\e".

-- 
Vincent Lefèvre <vincent@vinc17.net> - Web: <https://www.vinc17.net/>
100% accessible validated (X)HTML - Blog: <https://www.vinc17.net/blog/>
Work: CR INRIA - computer arithmetic / AriC project (LIP, ENS-Lyon)

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Bug#708979: closed by Gioele Barabucci <gioele@svario.it> (Re: Bug#708979: bash (readline): Something is wrong with binding keys to functions) Reuben Thomas <rrt@sc3d.org> - 2024-08-10 17:00 +0200
  Bug#708979: closed by Gioele Barabucci <gioele@svario.it> (Re: Bug#708979: bash (readline): Something is wrong with binding keys to functions) Vincent Lefevre <vincent@vinc17.net> - 2024-08-13 16:20 +0200
    Bug#708979: closed by Gioele Barabucci <gioele@svario.it> (Re: Bug#708979: bash (readline): Something is wrong with binding keys to functions) Reuben Thomas <rrt@sc3d.org> - 2024-08-13 17:40 +0200
      Bug#708979: closed by Gioele Barabucci <gioele@svario.it> (Re: Bug#708979: bash (readline): Something is wrong with binding keys to functions) Vincent Lefevre <vincent@vinc17.net> - 2024-08-13 18:50 +0200
        Bug#708979: closed by Gioele Barabucci <gioele@svario.it> (Re: Bug#708979: bash (readline): Something is wrong with binding keys to functions) Vincent Lefevre <vincent@vinc17.net> - 2024-08-13 19:00 +0200
        Bug#708979: closed by Gioele Barabucci <gioele@svario.it> (Re: Bug#708979: bash (readline): Something is wrong with binding keys to functions) Reuben Thomas <rrt@sc3d.org> - 2024-08-13 19:50 +0200

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