Tips – Page 9 – Guy Rutenberg

Bootstrap: Combining `input-append` and `input-block-level`

If you have a button appended to an input control in Bootstrap, and you want it fill the entire width, it’s not sufficient to add the input-block-level to the input itself but this CSS class also needs to be added to the surrounding .input-append div. For example:

<div class="input-append input-block-level">
	<input type="text" class="search-query input-block-level" name="q" placeholder="Search">
	<button type="submit" class="btn btn-primary">Search</button>
</div>

Applying .input-block-level to only one of the elments (either the div or the input) just doesn’t work.

Enabling C++11 (C++0x) in CMake

Going over some CMakeLists.txt files I’ve written, I came across the following snippet:

include(CheckCXXCompilerFlag)
CHECK_CXX_COMPILER_FLAG("-std=c++11" COMPILER_SUPPORTS_CXX11)
CHECK_CXX_COMPILER_FLAG("-std=c++0x" COMPILER_SUPPORTS_CXX0X)
if(COMPILER_SUPPORTS_CXX11)
	set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")
elseif(COMPILER_SUPPORTS_CXX0X)
	set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++0x")
else()
        message(STATUS "The compiler ${CMAKE_CXX_COMPILER} has no C++11 support. Please use a different C++ compiler.")
endif()

Various compiler versions of gcc and clang use different flags to specify C++11 support, namely older ones accept -std=c++0x and newer one -std=c++11. The above snippets detects which is the right one for the compiler being used and adds the flag to the CXX_FLAGS.

View `man` Pages Properly in gVim

Vim’s ability to display man pages easily using the K mapping often comes handy. It been bothering me for a while, that the same thing doesn’t work properly in gVim, which I use more. The reason is that Vim’s ability to display man pages depends on having a terminal emulator, which just isn’t true for gVim, hence the garbled display of man pages one sees if he tries viewing a man page in gVim.

Today, I found a way around this limitation. It turns out, Vim comes with support for displaying man pages in a split window, and does it perfectly – colors, links and all the necessary stuff. The first line, enables this feature which includes by default the K mapping to open the man page in a new split. The second part, which I find very convenient, makes the regular K do the same in gVim. And unlike the original mapping, it also accepts a count before, so pressing 3K will search the 3 man section of the keyword under the cursor.

" Properly display man pages
" ==========================
runtime ftplugin/man.vim
if has("gui_running")
	nnoremap K :<C-U>exe "Man" v:count "<C-R><C-W>"<CR>
endif

Highlight Whitespace at End-of-Line in Vim

Usually trailing whitespace is undesirable. Using vim’s :match command you can easily highlight those trailing whitespace:

:match Error /\s\+$/

This can be combined with autocmd and inserted to ~/.vimrc to highlight trailing whitespace only for certain files:

autocmd Filetype python match Error /\s\+$/

Preventing Directory Traversal in Python

Consider the following use case:

PREFIX = '/home/user/files/'
full_path = os.path.join(PREFIX, filepath)
read(full_path, 'rb')
...

Assuming that filepath is user-controlled, a malicious user user might attempt a directory traversal (like setting filepath to ../../../etc/passwd). How can we make sure that filepath cannot traverse “above” our prefix? There are of course numerous solutions to sanitizing input against directory traversalthat. The easiest way (that I came up with) to do so in python is:

filepath = os.normpath('/' + filepath).lstrip('/')

It works because it turns the path into an absolute path, normalizes it and makes it relative again. As one cannot traverse above /, it effectively ensures that the filepath cannot go outside of PREFIX.

Post updated: see the comments below for explanation of the changes.

Ubuntu Freezes When Booting with Degraded Raid

I tried testing my software raid (mdadm) setup by removing one of the disks. When I tried to boot the degraded system, the system hanged displaying a purple screen. If I try booting the system in recovery mode, I get the following error:

** WARNING: There appears to be one or more degraded RAID devices ** The system my have suffered a hardware fault, such as a disk drive failure. The root device may depend on the RAID devices being online. Do you wish to start the degraded RAID? [y/N]: — ** WARNING: There appears to be one or more degraded RAID devices **
The system my have suffered a hardware fault, such as a disk drive failure. The root device may depend on the RAID devices being online.
Do you wish to start the degraded RAID? [y/N]:

Galaxy S2 – Clearing Logs on an Unrooted Phone

I have a Samsung Galaxy S2 using an unrooted stock ROM. Lately, I couldn’t update any of my apps, or install new ones as every time I tried it would complain about Insufficient storage available. This was weird, as according to my phone the apps took less than 600MB and still I barely 200MB of free space in my device memory.

Using CyanogenMod’s Apps on Official ROM

Every since I switched back from using CyanogenMod ROM to the official ROM (due to modem problems) I missed some of the custom apps. It turns out to be really install those apps. You just need to download CyanogenMod and extract the relevant APKs from system/app/ and copy over the phone. To install them you’ll need to enable installation of apps from unknown source in Settings->Security. It’s best to get a CyanogenMod version that corresponds to your ROM’s version, but I successfully installed apps also from newer CyanogenMod releases.

Opening `mobi` and `epub` Files in Ubuntu

You can do it with Calibre and specifically with the ebook-viewer program that comes with it. However, for some reason the packagers didn’t ship a desktop file to accompany it, so you can’t just double-click on eBooks and have them opened correctly. This can be corrected by placing a ebook-viewer.desktop file in ~/.local/share/applications:

[Desktop Entry]
Version=1.0
Name=Ebook Viewer
Comment=Display .epub files and other e-books formats
Type=Application
Terminal=false
Icon=calibre
Exec=ebook-viewer %f
StartupWMClass=ebook-viewer
MimeType=application/x-mobipocket-ebook;application/epub+zip;
Categories=Graphics;Viewer;

Quickly Exiting Insert-Mode in Vim

Changing from insert mode to normal mode is usually quick. The other direction is more cumbersome. You either have to reach out for the escape key, or use the Ctrl-[ (which I never got used to).

After seeing a blog post suggesting to map jk to exit insert mode, I was inspired to create my own mapping. I chose kj because it’s faster to type, as typing inwards is faster than outwards (you can check for yourself by tapping with your fingers on your desk). To use it, add the following to your .vimrc:

:inoremap kj <ESC>

Now, whenever you are in insert mode, quickly typing kj will exit insert mode. It will introduce a short pause after typing k, but this is only a visual one, so it doesn’t actually slow you down. kj is one of the rarest bigrams in English, so you’ll almost never have to actually type it inside a text, but if you do, just wait a bit after typing k to type the j.

After writing this post, I’ve came across a Vim Wiki page listing all kinds of ways to avoid the escape key.

I’ve recently published my vimrc, take a look it might give you ideas for other neat tricks.