[Bug 1511154] Re: xdg-settings set <anything> fails with status 2 because of a small glitch

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I can also confirm this problem in 15.10.

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Title:
  xdg-settings set <anything> fails with status 2 because of a small
  glitch

Status in xdg-utils package in Ubuntu:
  Fix Released

Bug description:
  (Existing description has been broken up into sections.)

  [Impact]

  The first user-facing symptom: Google Chrome stable is correctly set
  as the default browser in System Settings / Details / Default
  Applications as well as in

  update-alternatives --display x-www-browser

  yet it keeps complaining about not being a default browser. Clicking
  "Make Google Chrome the default browser." on Chrome's settings page
  has no response.

  The problem is reported here http://askubuntu.com/questions/688779
  /google-chrome-stable-keeps-asking-if-it-should-be-set-to-default but
  the answer is somewhat wrong.

  [Test Case]

  I have successfully reproduced and debugged the problem. I managed to
  establish that it is connected to xdg-utils, namely to /usr/bin/xdg-
  settings script.

  michal at furia:~$ lsb_release -a
  No LSB modules are available.
  Distributor ID:	Ubuntu
  Description:	Ubuntu 15.10
  Release:	15.10
  Codename:	wily
  michal at furia:~$ xdg-settings get default-web-browser
  firefox.desktop
  michal at furia:~$ xdg-settings set default-web-browser google-chrome.desktop
  michal at furia:~$ echo $?
  2
  michal at furia:~$ xdg-settings get default-web-browser
  firefox.desktop

  There is a function in /usr/bin/xdg-settings called
  desktop_file_to_binary() and it has a bug. It is slightly different
  than the one in the vanilla xdg-utils 1.1.0 rc3. It is implemented in
  scripts/xdg-utils-common.in.

  See line 65 in xdg-utils-1.1.0~rc3+git20150907/scripts/xdg-utils-
  common.in :

  command="`grep -E "^Exec(\[[^]=]*])?=" "$file" | cut -d= -f 2- | sed
  -e 's/ .*$//'`"

  When executed against google-chrome.desktop or firefox.desktop it
  results with:

  google-chrome-stable
  google-chrome-stable
  google-chrome-stable

  or

  firefox
  firefox
  firefox

  respectively.

  When passed to `which` and then to `readlink -f` it results with no
  path to the actual binary. In the vanilla xdg-utils package (version
  1.1.0 rc3) the `sed` part is replaced with `first_word`. An
  alternative would be adding `| head -n 1`.

  Then we would have only one `google-chrome-stable` or `firefox` which
  in turn would result with the actual path to binary resolved correctly
  and that would make xdg-settings work fine.

  Also, it is possible to set Google Chrome as the default browser via
  its preferences and the aforementioned first user-facing symptom is
  gone.

  [Regression Potential]

  Limited. The commands after the modified lines assume that there is
  only one line, so passing the output of the modified lines through
  `head -n1` should ensure that. In the case of there being 0 or 1 lines
  before the `head -n1` command, nothing will be changed.

  In the worst case, there may exist a .desktop file where the first
  Exec line isn't the main program (mentioned in comment 2 below). In
  that case, however, this change will result in the incorrect program
  being chosen; this may or may not be better than the command not
  working at all.

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