Unix/Linux — Ubuntu/Debian — lock package version

In order to lock a package to a specific version and refrain it from being upgraded do:

sudo -s
echo PACKAGE_NAME hold | dpkg –set-selections

To verify the settings for a package to:

sudo -s
dpkg –get-selections PACKAGE_NAME

To re-enable a package to be upgraded do:

sudo -s
echo PACKAGE_NAME install | dpkg –set-selections

More info can be found here:
https://help.ubuntu.com/community/PinningHowto

Unix/Linux — .Xdefaults in X-Win32

In order to be able to use your .Xdefaults file in X-Win32 you have to do the following.

1. Copy your .Xdefaults file to C:\Users\USERNAME\AppData\ Local\StarNet\X-Win32\Xdefaults. Where USERNAME is your Windows user name.
2. Disable the Set Xresource Defaults option in the X-Win32 X-Config’s Window tab.

Unix/Linux — Insert TAB in command

If you need to run a command which requires you to insert a TAB, press Ctrl-V TAB to insert it.

This could be useful when you want to grep for TAB or split lines of a TAB separated file with cut.

Suversion — Change repository URL

If you have checked out a repository and the repository URL has changed, you can update the URL using the svn switch command. For example:

Old URL: https://www.oldrepo.com/svn/
New URL: https://www.newrepo.com/svn/

svn switch –relocate https://www.oldrepo.com/svn https://www.newrepo.com/svn

See svn switch in Version Control with Subversion book for more details.

Emacs — ispell — No word lists (Ubuntu)

In Ubuntu, if you get:

Error: No word lists can be found for the language “en_US”.

when trying to start ispell (e.g., M-x ispell-buffer) from Emacs, then you need to install the aspell-en package:

sudo apt-get install aspell-en

Emacs — Using rectangles

In Emacs, you can not only select by lines, but also by columns. If you select by columns, the selection is called a rectangle. You can use rectangles with the following shortcuts:

• C-@ or C-Space — start selection (as usual)
• M-x delete-rectangle or C-x r d — delete the rectangle delimited by the start selection and the current cursor position
• M-x kill-rectangle or C-x r k — then you can use — M-x yank-rectangle or C-x r y
• M-x clear-rectangle or C-x r c — replace the contents of the rectangle with spaces
• M-x open-rectangle or C-x r o — insert spaces in the area and push the original contents to the right

C/C++ — Insert sequential values into container

To insert sequential values into a container, you could use the iota function available in ext/numeric header. For example:

#include <ext/numeric>
#include <vector>
…

std::vector<int> v(5);
__gnu_cxx::iota(v.begin(), v.end(), 0);

v will contain {0, 1, 2, 3, 4}.

For more information see sgi documentation

Python — Convert string to HTML/XML entities

In order to convert a string to HTML/XML entities you can use:

”.join(['&#%d;' % ord(ch) for ch in text])

For example if text=’mailto’ the output would be:

‘& #109;& #97;& #105;& #108;& #116;& #111;’

This might be useful in hiding email addresses in web pages.

Unix/Linux — Swap Ctrl and Caps Lock in X11

In order to swap the Ctrl and Caps Lock keys in X11, you can add the following line in Section “InputDevice” of file /etc/X11/xorg.conf:

Option “XkbOptions” “ctrl:swapcaps”

If you woud like to keep the Ctrl where it is and make Caps Lock act as a Ctrl also, you can add:

Option “XkbOptions” “ctrl:nocaps”

Unix/Linux — generate large file

In order to generate a large file of a set size you can use:

dd if=/dev/zero of=test100M.bin bs=100000000 count=1

where of is the output file and bs is its size in bytes.