[Bug 1919185] Re: Bash completion breaks the content of $_ variable

[Mike Wescott]

This bug can lead to data loss:

$ echo aaa > aaa
$ echo bbb > bbb
$ mkdir tmp
$ mv a<tab> $_
$ mv b<tab> $_

Now the directory tmp is empty and there is bbb has been renamed
_filedir. The file aaa is nowhere to be found.

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https://bugs.launchpad.net/bugs/1919185

Title:
  Bash completion breaks the content of $_ variable

Status in bash package in Ubuntu:
  Confirmed

Bug description:
  In bash, the $_ variable ought to contain the last parameter of
  previous command. For example:

  $ touch aaa bbb
  $ cat aaa
  $ cat bbb $_

  the last line is equivalent to "cat bbb aaa".

  However, if I use bash completion to fill some other parameter like
  this:

  $ cat bb<TAB> $_

  (where <TAB> denotes hitting the TAB key), the value of the $_
  variable is overwritten with some mess, so that the result is: "cat:
  _filedir: No such file or directory"

  I expect this variable not to be overwritten and still contain the
  value "aaa", co that the command prints out the files bbb and aaa.

  This bug seems to be version-wide and usage-wide. I encounter this for
  many Ubuntu releases, for example, using Kubuntu 20.10. It can be
  reproduced even in terminal with no Xorg running.  The resulting error
  message differs according to what is being TAB-completed, for example
  with git command it says: "error: pathspec '__git_main' did not match
  any file(s) known to git".

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