Category Archives: GNU/Linux

Powerful Regular Expressions Combined with Lisp in Emacs

Regular expressions are a powerful text transformation tool. Any UNIX geek will tell you that. It’s so deeply ingrained into our culture, that we even make jokes about it. Another thing that we also love is having a powerful extension language at hand, and Lisp is one of the most powerful extension languages around (and of course, we make jokes about that too).

Emacs, one of the most famous Lisp applications today, has for a while now the ability to combine both of these, to reach entirely new levels of usefulness. Combining regular expressions and Lisp can do really magical things.

An example that I recently used a few times is parsing & de-humanizing numbers in dstat output. The output of dstat includes numbers that are printed with a suffix, like ‘B’ for bytes, ‘k’ for kilobytes and ‘M’ for megabytes, e.g.:

----system---- ----total-cpu-usage---- --net/eth0- -dsk/total- sda-
     time     |usr sys idl wai hiq siq| recv  send| read  writ|util
16-05 08:36:15|  2   3  96   0   0   0|  66B  178B|   0     0 |   0
16-05 08:36:16| 42  14  37   0   0   7|  92M 1268k|   0     0 |   0
16-05 08:36:17| 45  11  36   0   0   7|  76M 1135k|   0     0 |   0
16-05 08:36:18| 27  55   8   0   0  11|  67M  754k|   0    99M|79.6
16-05 08:36:19| 29  41  16   5   0  10| 113M 2079k|4096B   63M|59.6
16-05 08:36:20| 28  48  12   4   0   8|  58M  397k|   0    95M|76.0
16-05 08:36:21| 38  37  14   1   0  10| 114M 2620k|4096B   52M|23.2
16-05 08:36:22| 37  54   0   1   0   8|  76M 1506k|8192B   76M|33.6

So if you want to graph one of the columns, it’s useful to convert all the numbers in the same unit. Bytes would be nice in this case.

Separating all columns with ‘|’ characters is a good start, so you can use e.g. a CSV-capable graphing tool, or even simple awk scripts to extract a specific column. ‘C-x r t’ can do that in Emacs, and you end up with something like this:

|     time     |cpu|cpu|cpu|cpu|cpu|cpu|eth0 |eth0 | disk| disk|sda-|
|     time     |usr|sys|idl|wai|hiq|siq| recv| send| read| writ|util|
|16-05 08:36:15|  2|  3| 96|  0|  0|  0|  66B| 178B|   0 |   0 |   0|
|16-05 08:36:16| 42| 14| 37|  0|  0|  7|  92M|1268k|   0 |   0 |   0|
|16-05 08:36:17| 45| 11| 36|  0|  0|  7|  76M|1135k|   0 |   0 |   0|
|16-05 08:36:18| 27| 55|  8|  0|  0| 11|  67M| 754k|   0 |  99M|79.6|
|16-05 08:36:19| 29| 41| 16|  5|  0| 10| 113M|2079k|4096B|  63M|59.6|
|16-05 08:36:20| 28| 48| 12|  4|  0|  8|  58M| 397k|   0 |  95M|76.0|
|16-05 08:36:21| 38| 37| 14|  1|  0| 10| 114M|2620k|4096B|  52M|23.2|
|16-05 08:36:22| 37| 54|  0|  1|  0|  8|  76M|1506k|8192B|  76M|33.6|

The leading and trailing ‘|’ characters are there so we can later use orgtbl-mode, an awesome table editing and realignment tool of Emacs. Now to the really magical step: regular expressions and lisp working together.

What we would like to do is convert text like “408B” to just “408”, text like “1268k” to the value of (1268 * 1024), and finally text like “67M” to the value of (67 * 1024 * 1024). The first part is easy:

M-x replace-regexp RET \([0-9]+\)B RET \1 RET

This should just strip the “B” suffix from byte values.

For the kilobyte and megabyte values what we would like is to be able to evaluate an arithmetic expression that involves \1. Something like “replace \1 with the value of (expression \1)“. This is possible in Emacs by prefixing the substitution pattern with \,. This instructs Emacs to evaluate the rest of the substitution pattern as a Lisp expression, and use its string representation as the “real” substitution text.

So if we match all numeric values that are suffixed by ‘k’, we can use (string-to-number \1) to convert the matching digits to an integer, multiply by 1024 and insert the resulting value by using the following substitution pattern:

\,(* 1024 (string-to-number \1))

The full Emacs command would then become:

M-x replace-regexp RET \([0-9]+\)k RET \,(* 1024 (string-to-number \1)) RET

This, and the byte suffix removal, yield now the following text in our Emacs buffer:

|     time     |cpu|cpu|cpu|cpu|cpu|cpu|eth0 |eth0 | disk| disk|sda-|
|     time     |usr|sys|idl|wai|hiq|siq| recv| send| read| writ|util|
|16-05 08:36:15|  2|  3| 96|  0|  0|  0|  66| 178|   0 |   0 |   0|
|16-05 08:36:16| 42| 14| 37|  0|  0|  7|  92M|1298432|   0 |   0 |   0|
|16-05 08:36:17| 45| 11| 36|  0|  0|  7|  76M|1162240|   0 |   0 |   0|
|16-05 08:36:18| 27| 55|  8|  0|  0| 11|  67M| 772096|   0 |  99M|79.6|
|16-05 08:36:19| 29| 41| 16|  5|  0| 10| 113M|2128896|4096|  63M|59.6|
|16-05 08:36:20| 28| 48| 12|  4|  0|  8|  58M| 406528|   0 |  95M|76.0|
|16-05 08:36:21| 38| 37| 14|  1|  0| 10| 114M|2682880|4096|  52M|23.2|
|16-05 08:36:22| 37| 54|  0|  1|  0|  8|  76M|1542144|8192|  76M|33.6|

Note: Some of the columns are indeed not aligned very well. We’ll fix that later. On to the megabyte conversion:

M-x replace-regexp RET \([0-9]+\)M RET \,(* 1024 1024 (string-to-number \1)) RET

Which produces a version that has no suffixes at all:

|     time     |cpu|cpu|cpu|cpu|cpu|cpu|eth0 |eth0 | disk| disk|sda-|
|     time     |usr|sys|idl|wai|hiq|siq| recv| send| read| writ|util|
|16-05 08:36:15|  2|  3| 96|  0|  0|  0|  66| 178|   0 |   0 |   0|
|16-05 08:36:16| 42| 14| 37|  0|  0|  7|  96468992|1298432|   0 |   0 |   0|
|16-05 08:36:17| 45| 11| 36|  0|  0|  7|  79691776|1162240|   0 |   0 |   0|
|16-05 08:36:18| 27| 55|  8|  0|  0| 11|  70254592| 772096|   0 |  103809024|79.6|
|16-05 08:36:19| 29| 41| 16|  5|  0| 10| 118489088|2128896|4096|  66060288|59.6|
|16-05 08:36:20| 28| 48| 12|  4|  0|  8|  60817408| 406528|   0 |  99614720|76.0|
|16-05 08:36:21| 38| 37| 14|  1|  0| 10| 119537664|2682880|4096|  54525952|23.2|
|16-05 08:36:22| 37| 54|  0|  1|  0|  8|  79691776|1542144|8192|  79691776|33.6|

Finally, to align everything in neat, pipe-separated columns, we enable M-x orgtbl-mode, and type “C-c C-c” with the pointer somewhere inside the transformed dstat output. The buffer now becomes something usable for pretty-much any graphing tool out there:

| time           | cpu | cpu | cpu | cpu | cpu | cpu |      eth0 |    eth0 |  disk |      disk | sda- |
| time           | usr | sys | idl | wai | hiq | siq |      recv |    send |  read |      writ | util |
| 16-05 08:36:15 |   2 |   3 |  96 |   0 |   0 |   0 |        66 |     178 |     0 |         0 |    0 |
| 16-05 08:36:16 |  42 |  14 |  37 |   0 |   0 |   7 |  96468992 | 1298432 |     0 |         0 |    0 |
| 16-05 08:36:17 |  45 |  11 |  36 |   0 |   0 |   7 |  79691776 | 1162240 |     0 |         0 |    0 |
| 16-05 08:36:18 |  27 |  55 |   8 |   0 |   0 |  11 |  70254592 |  772096 |     0 | 103809024 | 79.6 |
| 16-05 08:36:19 |  29 |  41 |  16 |   5 |   0 |  10 | 118489088 | 2128896 |  4096 |  66060288 | 59.6 |
| 16-05 08:36:20 |  28 |  48 |  12 |   4 |   0 |   8 |  60817408 |  406528 |     0 |  99614720 | 76.0 |
| 16-05 08:36:21 |  38 |  37 |  14 |   1 |   0 |  10 | 119537664 | 2682880 |  4096 |  54525952 | 23.2 |
| 16-05 08:36:22 |  37 |  54 |   0 |   1 |   0 |   8 |  79691776 | 1542144 |  8192 |  79691776 | 33.6 |

The trick of combining arbitrary Lisp expressions with regexp substitution patterns like \1, \2\9 is something I have found immensely useful in Emacs. Now that you know how it works, I hope you can find even more amusing use-cases for it.

Update: The Emacs manual has a few more useful examples of \, in action, as pointed out by tunixman on Twitter.

Speeding Up Emacs and Parsing Emacs Lisp from Emacs Lisp

I recently spent a bit of time to clean up all the cruft that my ~/.emacs file and my ~/elisp directory had accumulated. I have been using a multi-file setup to configure my Emacs sessions, since at least 2008. This turned out to be a royal mess after 5+ years of patching stuff without a very clear plan or structure. The total line-count of both my ~/.emacs and all the *.el files I had imported into my ~/elisp directory was almost 20,000 lines of code:

$ wc -l BACKUP/.emacs $( find BACKUP/elisp -name '*.el')
   119 BACKUP/.emacs
    84 BACKUP/elisp/keramida-w3m.el
    90 BACKUP/elisp/keramida-keys.el
   156 BACKUP/elisp/keramida-irc.el
  5449 BACKUP/elisp/erlang.el
   892 BACKUP/elisp/fill-column-indicator.el
   344 BACKUP/elisp/keramida-erc.el
    87 BACKUP/elisp/keramida-chrome.el
    89 BACKUP/elisp/keramida-autoload.el
   141 BACKUP/elisp/keramida-ui.el
    42 BACKUP/elisp/keramida-slime.el
  1082 BACKUP/elisp/ace-jump-mode.el
     2 BACKUP/elisp/scala-mode2/scala-mode2-pkg.el
   907 BACKUP/elisp/scala-mode2/scala-mode2-indent.el
    26 BACKUP/elisp/scala-mode2/scala-mode2-lib.el
   502 BACKUP/elisp/scala-mode2/scala-mode2-fontlock.el
    37 BACKUP/elisp/scala-mode2/scala-mode2-map.el
   808 BACKUP/elisp/scala-mode2/scala-mode2-syntax.el
   111 BACKUP/elisp/scala-mode2/scala-mode2.el
   121 BACKUP/elisp/scala-mode2/scala-mode2-paragraph.el
  1103 BACKUP/elisp/php-mode.el
   142 BACKUP/elisp/themes/cobalt-theme.el
   665 BACKUP/elisp/themes/zenburn-theme.el
   142 BACKUP/elisp/themes/sublime-themes/cobalt-theme.el
    80 BACKUP/elisp/themes/tomorrow-night-blue-theme.el
    80 BACKUP/elisp/themes/tomorrow-night-eighties-theme.el
   115 BACKUP/elisp/themes/tomorrow-theme.el
    80 BACKUP/elisp/themes/tomorrow-night-bright-theme.el
   339 BACKUP/elisp/cmake-mode.el
    95 BACKUP/elisp/keramida-cc-extra.el
  1341 BACKUP/elisp/lua-mode.el
  2324 BACKUP/elisp/markdown-mode.el
   184 BACKUP/elisp/rcirc-notify.el
   167 BACKUP/elisp/keramida-defaults.el
   203 BACKUP/elisp/keramida-hooks.el
    43 BACKUP/elisp/keramida-lang.el
   435 BACKUP/elisp/edit-server.el
   709 BACKUP/elisp/slang-mode.el
    66 BACKUP/elisp/keramida-eshell.el
 19402 total

20,000 lines of code is far too much bloat. It’s obvious that this was getting out of hand, especially if you consider that I had full configuration files for at least two different IRC clients (rcirc and erc) in this ever growing blob of complexity.

What I did was make a backup copy of everything in ~/BACKUP and start over. This time I decided to go a different route from 2008 though. All my configuration lives in a single file, in ~/.emacs, and I threw away any library from my old ~/elisp tree which I haven’t actively used in the past few weeks. I imported the rest of them into the standard user-emacs-directory of modern Emacsen: at ~/.emacs.d/. I also started using eval-after-load pretty extensively, to speed up the startup of Emacs, and only configure extras after the related packages are loaded. This means I could trim down the list of preloaded packages even more.

The result, as I tweeted yesterday was an impressive speedup of the entire startup process of Emacs. Now it can start, load everything and print a message in approximately 0.028 seconds, which is more than 53 times faster than the ~1.5 seconds it required before the cleanup!

I suspected that the main contributor to this speedup was the increased use of eval-after-load forms, but what percentage of the entire file used them?

So I wrote a tiny bit of Emacs Lisp to count how many times each top-level forms appears in my new ~/.emacs file:

(defun file-forms-list (file-name)
  (let ((file-forms nil))
    ;; Keep reading Lisp expressions, until we hit EOF,
    ;; and just add one entry for each toplevel form
    ;; to `file-forms'.
    (condition-case err
        (with-temp-buffer
          (insert-file file-name)
          (goto-char (point-min))
          (while (< (point) (point-max))
            (let* ((expr (read (current-buffer)))
                   (form (first expr)))
              (setq file-forms (cons form file-forms)))))
      (end-of-file nil))
    (reverse file-forms)))

(defun file-forms-alist (file-name)
  (let ((forms-table (make-hash-table :test #'equal)))
    ;; Build a hash that maps form-name => count for all the
    ;; top-level forms of the `file-name' file.
    (dolist (form (file-forms-list file-name))
      (let ((form-name (format "%s" form)))
        (puthash form-name (1+ (gethash form-name forms-table 0))
                 forms-table)))
    ;; Convert the hash table to an alist of the form:
    ;;    ((form-name . count) (form-name-2 . count-2) ...)
    (let ((forms-alist nil))
      (maphash (lambda (form-name form-count)
                 (setq forms-alist (cons (cons form-name form-count)
                                         forms-alist)))
               forms-table)
      forms-alist)))

(progn
  (insert "\n")
  (insert (format "%7s %s\n" "COUNT" "FORM-NAME"))
  (let ((total-forms 0))
    (dolist (fc (sort (file-forms-alist "~/.emacs")
                      (lambda (left right)
                        (> (cdr left) (cdr right)))))
      (insert (format "%7d %s\n" (cdr fc) (car fc)))
      (setq total-forms (+ total-forms (cdr fc))))
    (insert (format "%7d %s\n" total-forms "TOTAL"))))

Evaluating this in a scratch buffer shows output like this:

COUNT FORM-NAME
   32 setq-default
   24 eval-after-load
   14 set-face-attribute
   14 global-set-key
    5 autoload
    4 require
    4 setq
    4 put
    3 defun
    2 when
    1 add-hook
    1 let
    1 set-display-table-slot
    1 fset
    1 tool-bar-mode
    1 scroll-bar-mode
    1 menu-bar-mode
    1 ido-mode
    1 global-hl-line-mode
    1 show-paren-mode
    1 iswitchb-mode
    1 global-font-lock-mode
    1 cua-mode
    1 column-number-mode
    1 add-to-list
    1 prefer-coding-system
  122 TOTAL

This showed that I’m still using a lot of setq-default forms: 26.23% of the top-level forms are of this type. Some of these may still be candidates for lazy initialization, since I can see that many of them are indeed mode-specific, like these two:

(setq-default diff-switches "-u")
(setq-default ps-font-size '(8 . 10))

But eval-after-load is a close second, with 19.67% of all the top-level forms. That seems to agree with the original idea of speeding up the startup of everything by delaying package-loading and configuration until it’s actually needed.

10 of the remaining forms are one-off mode setting calls, like (tool-bar-mode -1), so 8.2% of the total calls is probably going to stay this way for a long time. That’s probably ok though, since the list includes several features I find really useful, very very often.

Saving Space in Rsnapshot Archives with Hardlinks

The hardlink package is quite handy on Linux systems. It appears to do a nice job saving disk space in my local rsnapshot archives (25 GB reported as “saved” after today’s run on a week of daily snapshots). The stress put on my external USB backup disk wasn’t too extreme either, as reported by Munin’s IO/sec graphs for /dev/sdc:

IO/sec graph for a USB disk, while hardlink was running on a collection of rsnapshot daily archives.

IO/sec graph for a USB disk, while hardlink was running on a collection of rsnapshot daily archives.

That’s a lot of read operations, and then a percentage of them converted back to writes, when hardlink(1) discovers duplicate files and replaces them with hard links. Which is exactly the sort of behavior we’d expect from this sort of thing.

The hardlink invocation that triggered these I/O operation was quite mundane:

# time hardlink -f -m -v *home.*
[output stats ellided]
        1380.243 real   17.525 user     47.975 sys

Having run for a little over 23m it managed to hardlink enough files in my daily laptop backup snapshots to save 25 GB of disk space. I think it was worth the time vs. space trade-off :-)

Controlling the Keyboard Backlight from CLI

I found out today how to query and set the state of the keyboard backlight of my Asus Zenbook laptop through dbus-send calls, so I instantly thought “hey this would be nice to have in a shell script”.

So I wrote a small script called “backlight“, whose basic usage is a simple set of three commands:

backlight up
backlight down
backlight [ 0 | 1 | 2 | 3 ]

With this script installed as ‘~/bin/backlight’ in my home directory I can control the brightness of my keyboard’s backlight with simple shell commands, which is rather convenient, because all that usually runs on my desktop is a tiling window manager and a couple of terminals.

The script itself is rather small and it may be useful to someone else too, so here it is:

#!/bin/sh

# backlight_get
#       Print current keyboard brightness from UPower to stdout.
backlight_get()
{
    dbus-send --type=method_call --print-reply=literal --system         \
        --dest='org.freedesktop.UPower'                                 \
        '/org/freedesktop/UPower/KbdBacklight'                          \
        'org.freedesktop.UPower.KbdBacklight.GetBrightness'             \
        | awk '{print $2}'
}

# backlight_get_max
#       Print the maximum keyboard brightness from UPower to stdout.
backlight_get_max()
{
    dbus-send --type=method_call --print-reply=literal --system       \
        --dest='org.freedesktop.UPower'                               \
        '/org/freedesktop/UPower/KbdBacklight'                        \
        'org.freedesktop.UPower.KbdBacklight.GetMaxBrightness'        \
        | awk '{print $2}'
}

# backlight_set NUMBER
#       Set the current backlight brighness to NUMBER, through UPower
backlight_set()
{
    value="$1"
    if test -z "${value}" ; then
        echo "Invalid backlight value ${value}"
    fi

    dbus-send --type=method_call --print-reply=literal --system       \
        --dest='org.freedesktop.UPower'                               \
        '/org/freedesktop/UPower/KbdBacklight'                        \
        'org.freedesktop.UPower.KbdBacklight.SetBrightness'           \
        "int32:${value}}"
}

# backlight_change [ UP | DOWN | NUMBER ]
#       Change the current backlight value upwards or downwards, or
#       set it to a specific numeric value.
backlight_change()
{
    change="$1"
    if test -z "${change}" ; then
        echo "Invalid backlight change ${change}."                    \
            "Should be 'up' or 'down'." >&2
        return 1
    fi

    case ${change} in
    [1234567890]|[[1234567890][[1234567890])
        current=$( backlight_get )
        max=$( backlight_get_max )
        value=$( expr ${change} + 0 )
        if test ${value} -lt 0 || test ${value} -gt ${max} ; then
            echo "Invalid backlight value ${value}."                  \
                "Should be a number between 0 .. ${max}" >&2
            return 1
        else
            backlight_set "${value}"
            notify-send -t 800 "Keyboard brightness set to ${value}"
        fi
        ;;

    [uU][pP])
        current=$( backlight_get )
        max=$( backlight_get_max )
        if test "${current}" -lt "${max}" ; then
            value=$(( ${current} + 1 ))
            backlight_set "${value}"
            notify-send -t 800 "Keyboard brightness set to ${value}"
        fi
        ;;

    [dD][oO][wW][nN])
        current=$( backlight_get )
        if test "${current}" -gt 0 ; then
            value=$(( ${current}  - 1 ))
            backlight_set "${value}"
            notify-send -t 800 "Keyboard brightness set to ${value}"
        fi
        ;;

    *)
        echo "Invalid backlight change ${change}." >&2
        echo "Should be 'up' or 'down' or a number between"           \
            "1 .. $( backlight_get_max )" >&2
        return 1
        ;;
    esac
}

if test $# -eq 0 ; then
    current_brightness=$( backlight_get )
    notify-send -t 800 "Keyboard brightness is ${current_brightness}"
else
    # Handle multiple backlight changes, e.g.:
    #   backlight.sh up up down down up
    for change in "$@" ; do
        backlight_change "${change}"
    done
fi

Fixing Shifted-Arrow Keys in 256-Color Terminals on Linux

The terminfo entry for “xterm-256color” that ships by default as part of ncurses-base on Debian Linux and its derivatives is a bit annoying. In particular, shifted up-arrow key presses work fine in some programs, but fail in others. It’s a bit of a gamble if Shift-Up works in joe, pico, vim, emacs, mutt, slrn, or what have you.

THis afternoon I got bored enough of losing my selected region in Emacs, because I forgot that I was typing in a terminal launched by a Linux desktop. SO I thought “what the heck… let’s give the FreeBSD termcap entry for xterm-256color a try”:

keramida> scp bsd:/etc/termcap /tmp/termcap-bsd
keramida> captoinfo -e $(                                  \
  echo $( grep '^xterm' termcap | sed -e 's/[:|].*//' ) |  \
  sed -e 's/ /,/g'                                         \
  ) /tmp/termcap  > /tmp/terminfo.src
keramida> tic /tmp/terminfo.src

Restarted my terminal, and quite unsurprisingly, the problem of Shift-Up keys was gone.

The broken xterm-256color terminfo entry from /lib/terminfo/x/xterm-256color is now shadowed by ~/.terminfo/x/xterm-256color, and I can happily keep typing without having to worry about losing mental state because of this annoying little misfeature of Linux terminfo entries.

The official terminfo database sources[1], also work fine. So now I think some extra digging is required to see what ncurses-base ships with. There’s definitely something broken in the terminfo entry of ncurses-base, but it will be nice to know which terminal capabilities the Linux package botched.

Notes:
[1] http://invisible-island.net/ncurses/ncurses.faq.html#which_terminfo

Mate desktop support for xdg-open (tiny patch)

The Mate desktop really lives up to its promise of a “traditional desktop”, compatible in look and feel with Gnome 2.X versions.

After running it for a few hours now, I’m sold. I never really liked Unity very much, so Mate feels like ‘home’.

There are a few minor things that need tweaking though, mostly because the desktop is no longer called ‘Gnome’. One of them is the default xdg-open script that ships with the xdg-utils package. The current version of the script assumes that the desktop is called one of ‘KDE’, ‘LXDE’, ‘gnome’ or something else. The detectDE() function fails to recognize Mate, because it tries to look for GNOME_DESKTOP_SESSION_ID in its environment, and this is obviously no longer there for Mate.

The following patch fixes that, by checking for the string 'mate' in DESKTOP_SESSION instead, and adding a tiny bit of dispatch code based on DE='mate' further down, to call a new open_mate() function.

--- xdg-open.orig	2013-03-18 12:39:07.955516232 +0100
+++ xdg-open	2013-03-18 12:38:45.955515638 +0100
@@ -308,6 +308,7 @@
     elif `dbus-send --print-reply --dest=org.freedesktop.DBus /org/freedesktop/DBus org.freedesktop.DBus.GetNameOwner string:org.gnome.SessionManager > /dev/null 2>&1` ; then DE=gnome;
     elif xprop -root _DT_SAVE_MODE 2> /dev/null | grep ' = \"xfce4\"$' >/dev/null 2>&1; then DE=xfce;
     elif [ x"$DESKTOP_SESSION" = x"LXDE" ]; then DE=lxde;
+    elif [ x"$DESKTOP_SESSION" = x'mate' ]; then DE=mate;
     else DE=""
     fi
 }
@@ -371,6 +372,21 @@
     fi
 }
 
+open_mate()
+{
+    if gvfs-open --help 2>/dev/null 1>&2; then
+        gvfs-open "$1"
+    else
+        mate-open "$1"
+    fi
+
+    if [ $? -eq 0 ]; then
+        exit_success
+    else
+        exit_failure_operation_failed
+    fi
+}
+
 open_xfce()
 {
     exo-open "$1"
@@ -545,6 +561,10 @@
     open_gnome "$url"
     ;;
 
+    mate)
+    open_mate "$url"
+    ;;
+
     xfce)
     open_xfce "$url"
     ;;

Now this is a tiny problem, but it’s one that improves the usability of Mate for every-day stuff. One of the things that this fixes it the handling of magnet: links in Chrome. When Chrome tries to open magnet: links without this patch, it seems to “do nothing” but open a new tab and stop. With this patch applied, xdg-open works fine for magnet links (depending on your current MIME application settings too, of course), and Chrome happily opens torrent links in Mate desktops without a glitch.

Mutt-like Scrolling for Gnus

Mutt scrolls the index of email folders up or down, one line at a time, with the press of a single key: ‘<‘ or ‘>’. This is a very convenient way to skim through email folder listings, so I wrote a small bit of Emacs Lisp to do the same in Gnus tonight.

;;;
;; Scrolling like mutt for group, summary, and article buffers.
;;
;; Being able to scroll the current buffer view by one line with a
;; single key, rather than having to guess a random number and recenter
;; with `C-u NUM C-l' is _very_ convenient.  Mutt binds scrolling by one
;; line to '<' and '>', and it's something I often miss when working
;; with Gnus buffers.  Thanks to the practically infinite customizability
;; of Gnus, this doesn't have to be an annoyance anymore.

(defun keramida-mutt-like-scrolling ()
  "Set up '<' and '>' keys to scroll down/up one line, like mutt."
  ;; mutt-like scrolling of summary buffers with '<' and '>' keys.
  (local-set-key (kbd ">") 'scroll-up-line)
  (local-set-key (kbd "<") 'scroll-down-line))

(add-hook 'gnus-group-mode-hook 'keramida-mutt-like-scrolling)
(add-hook 'gnus-summary-mode-hook 'keramida-mutt-like-scrolling)
(add-hook 'gnus-article-prepare-hook 'keramida-mutt-like-scrolling)

This is now the latest addition to my ~/.gnus startup code, and we’re one step closer to making Gnus behave like my favorite old-time mailer.