Lexical illusions are very hard to find when proofreading. The most common lexical illusion is a duplicated word, as in this well-known example: A lexical illusion: many people are not aware that the the brain will automatically ignore a second instance of the word 'the' when it starts a new line. …

Swapping the rows and columns in a table on the command line would seem to be a fairly easy thing to do. For example, with this tab-separated table (called 'tabbed') as input: get this tab-separated table ('swapped') as output: Datamash Transposing rows and columns is indeed easy if you have the…

Backreferences are part of the complicated and sometimes confusing world of regular expressions. The basic idea is this: you can substitute any part of a regular expression with a backslash followed by a number, so long as you surround the part to be substituted with round brackets. The command…

Most people store and organise their personal emails as individual files (messages) in folders. Those folders might be on a webmail company's servers, or in a mail client program on the user's personal computer. In both cases the emails are probably in a special email format. I'm horribly…

I recently scripted a GUI dialog that lists my 10 most recently modified files in reverse chronological order and allows me to choose more than 1 file for opening. The dialog is launched with a keyboard shortcut and is shown here with 2 files selected: The script is in copy-and-paste form at the…

My wife likes to organise and store information in Gnumeric spreadsheets. Every now and then she needs to filter her data and save the result to a new spreadsheet. Gnumeric doesn't have a simple way to do that. It has a complicated way to do it ('Advanced Filter'), but nothing so straightforward as…

You can store a code snippet in a shell alias or a function, but when you type the alias or function name in a BASH shell and press 'Enter', the shell executes (or tries to execute) the snippet. That's no good if the snippet is incomplete or needs editing. A simple workaround is to paste the…

The file I'll be using for this demonstration is called demo and looks like this: demo is plain text with 2 tab-separated columns. The first column is sorted alphabetically, but the second column isn't sorted. What I want to find out is how many different letters are in the second column for each…

I worked on these bits of code to simplify a shell script of mine. You really wouldn't want to see the script's original commands here — they're way too ugly! The new commands are much prettier and work well. The problem To simplify the story, here's a comma-separated table called demo, sorted on t…

No, these aren't homework problems from a computer science class. They're interesting head-scratchers based on a data-analysis project I worked on recently, with the data 'reimagined' here for simplicity but with the underlying problems intact. We'll start with boys and girls, which are text files…