How to use Vim as plain text editor

Vim is not only useful for code, but also as a general plain text editor. This is useful for writing README files, Markdown files or if you like publishing plain text file content.

In plain text files, a desirable property is to have lines wrapped at a certain width. The general wrap feature of Vim is meaningful only for code which has long lines. This option just wraps the long line visually to the screen width.

To use Vim as a plain text editor you want it to automatically breaks lines at a certain width as you type. You want it to do that only at word boundaries. The option that enables this mode is textwidth. For source code, this feature is disabled and is set to 0.

To enable Vim to set a maximum width for text that is inserted, set this option: :set textwidth=80

If you have existing text that was not set to this width or you have shortened some lines all of that can be fixed too: mark them visually and press gq.

A final feature needed from a plain text editor is to be able to center a line. This is useful for example for titles and section headings. To do that, mark that line visually and type :center. This only works if the textwidth option is set.

Tried with: Vim 8.0 and Ubuntu 18.04


How to use clang-tidy

clang-tidy is a LLVM tool that can be used as a static checker on your C++ codebase and to fix errors it finds. A full list of current checks and their descriptions can be found here. The number of checks available to you will depend on the clang-tidy version you are using.

  • Installing this tool is easy:
$ sudo apt install clang-tidy

This typically installs a stable but older version of the tool with less number of checks.

  • To list the checks it performs by default:
$ clang-tidy -list-checks

On my computer I found it had 80 checks enabled by default.

  • To list all the checks that it can perform:
$ clang-tidy -list-checks -checks="*"

On my computer I found that it had a total of 292 checks.

  • To check a file using all checks enabled by default:
$ clang-tidy foobar.cpp
  • To check a file using all checks enabled by default and fix the errors using suggested fixes:
$ clang-tidy -fix foobar.cpp
$ clang-tidy -fix-errors foobar.cpp
  • To use a specific check, say modernize-use-nullptr:
$ clang-tidy -checks="-*,modernize-use-nullptr" foobar.cpp

Tried with: clang-tidy 6.0.0 and Ubuntu 18.04

How to fix header guards using guardonce

Header guards are used in C and C++ header files to avoid them being included more than once during the compilation of a compilation unit. There are generally two techniques: using an include guard and using a pragma once directive. guardonce provides a set of Python tools that can be used to diagnose the state of header guards, convert between the two types of guards and to fix guards in your codebase.

  • Installing guardonce using pip is easy:
$ sudo pip3 install guardonce
  • To convert include guards to pragma onces for all header files in the current directory:
$ guard2once *.h
  • To convert pragma onces to include guards for all header files in the current directory:
$ once2guard *.h
  • The tools support a pattern language that can be used to specify include guard name of a specific pattern. The pattern is built like a Unix pipeline. For example, to convert pragma once to include guard names with a default prefix (say FOOBAR_) followed by filename in snake form and uppercase:
$ once2guard -p "name | snake | upper | prepend FOOBAR_" *.h

For a filename linkedList.h the above command would generate an include guard name FOOBAR_LINKED_LIST_H.

  • For include guards it is convenient to have the guard name to appear in comments near the endif. To do that:
$ once2guard -s "#endif // %" *.h
  • It is a good convenience to have a newline before the endif. To do that:
$ once2guard -l *.h
  • There is no straightforward option to fix or modify the include guards to a certain pattern. Instead I found that I could achieve this by first converting the file to pragma once and then converting back to include guards. This can be done like this:
$ guard2once *.h ; once2guard *.h

Tried with: guardonce 2.4.0 and Ubuntu 18.04

Unix date tool

date is the Unix tool to check both the date and the time from the shell in Linux, Cygwin and other Unix-like systems. There is no separate tool to show the time. date is part of the GNU Coreutils package.

  • By default, the tool displays the local time in your local format. On my computer, the format was like this:
$ date
Mon, Jan 21, 2019  8:42:23 AM
  • To view the UTC time:
$ date -u
  • To view the modification time of a file:
$ date -r foobar.txt

How to get last argument of previous command in Fish

While working at the Bash shell prompt, you can access the very last argument of the preceding command using $_.

For example:

$ vim foobar.txt
$ vim $_

To get the effect of $_ in Fish, press Alt+Up. Fish will insert the last argument of the previous command for you right there at the shell prompt.

If you find this command is not working, please check if your terminal multiplexer (tmux or Byobu) or your GUI terminal or windowing environment has not already assigned that key for something else.

How to copy retaining relative path


From a certain directory I wanted to copy a file a/b/c.txt to a destination. But I wanted the relative path a/b to be retained at the destination. A normal copy would just copy c.txt to the destination.


There is no way to do this using the cp command. One solution is to use rsync which supports maintaining the relative file path.

For example:

$ pwd
$ rsync -R a/b/c.txt /home/joe/destination

This copies c.txt to /home/joe/destination/a/b automatically creating a/b if they do not exist in the destination.

Embedded Software Development for Safety-Critical Systems

Chris Hobbs is a safety engineer who works on the QNX real-time operating system. I discovered him while reading QNX documentation and that led to reading his book Embedded Software Development for Safety-Critical Systems. This book is a practical introduction for software engineers who need to develop software that is compliant to functional safety standards such as IEC 61508 and ISO 26262.

I picked up the book precisely because these IEC/ISO standards are incredibly hard to digest. This book turned out to be truly a breath of fresh air. It cut through so much of the jargon used in the above standards giving simple and elegant meanings and illustrations for all of them. For example, normal English words like fault, error and failure have distinct and precise meanings in the safety world. And when reading and writing in this space one needs to be clearly aware of these meanings.

The author has loads of experience in the safety systems field and that helps when he gives his personal opinion of many of the recommendations and procedures set forth by these standards. There is a large section of the book given to fault analysis and formal verification which I am not sure how most software would undergo.

Minor quibbles aside, I found this book to be truly enlightening and only wished it was longer and covered more of the software development process for general and more complex software that cannot undergo formal verification. If you are looking to comply to standards such as IEC/ISO this book seems like a perfect no-nonsense introductory text.

Find duplicate files using fdupes

fdupes is a great little tool that can be used to find duplicate files inside one or more directories. It does this by checking the file sizes, MD5 hashes and a byte for byte comparison of the files.

  • To install the tool:
$ sudo apt install fdupes
  • To ask the tool to find and list duplicate files inside a directory foobar:
$ fdupes -r foobar/

Tried with: fdupes 1.6.1 and Ubuntu 18.04

How to negate image using ImageMagick

The ImageMagick convert tool can be used to negate an image using the -negate and +negate options. -negate replaces every grayscale or RGB pixel with its inverted or complementary color. Use +negate when you want to restrict this operation to only work on grayscale pixels.


$ convert -negate foo.png inverted_foo.png

Tried with: ImageMagick 6.9.7 and Ubuntu 18.04

How to play WRF file

Cisco Webex sessions can be recorded and the recordings can be saved as WRF and ARF files. There does not seem to be any player for the WRF file format on Linux. If you are using Windows or Mac, you can use the Webex Player here to view the files. There is also a Webex Recording Editor that is available on the same webpage that can be used to render a WRF file to a WMV file. I tried the players and editor on Windows, and they seem to be extremely old Windows apps with basic functionality.