pattern

A large collection of Unix/Linux ‘grep’ command examples

Linux grep commands FAQ: Can you share some Linux/Unix grep command examples?

Sure. The name grep means "general regular expression parser", but you can think of the grep command as a "search" command for Unix and Linux systems: it's used to search for text strings and more-complicated "regular expressions" within one or more files.

I think it's easiest to learn how to use the grep command by showing examples, so let's dive right in.

Scala/Java: How to write a pattern that matches a minimum to maximum number of specified characters

If you’re using Java or Scala and need to write a pattern that matches a range of characters, where those characters occur between a minimum and maximum number of times in the pattern, the following example shows a solution I’m currently using.

The idea is that the pattern "[a-zA-Z0-9]{1,4}" means, “Match a string that has only the characters a-z, A-Z, and 0-9, where those characters occur a minimum of one time and a maximum of four times.” The following tests in the Scala REPL shows how this works:

A Scala shell script to insert text before a matching pattern

I don’t remember exactly why I wrote this Scala shell script, but if I remember right I was having a problem getting sed to work properly, so I wrote this little script to insert an Amazon Kindle “break” tag before each <h1> tag in an HTML file:

sed on macOS: How to append multiple lines of text to an HTML or XML file alvin December 19, 2017 - 3:40pm

As a brief note about the Linux/Unix sed command, today I learned how to append multiple lines of text to an HTML (or XML) file on macOS. The short answer is that I created a sed commands file named changes.sed with these contents:

How to write “If string starts with” in Drupal 8 Twig templates

If you ever need to write a “string starts with” comparison in Drupal 8 Twig templates, I just used this approach in a node.html.twig template file and I can confirm that it works:

{% if uri starts with '/foo' %}

More accurately, what I did was to first get the URI for the current Drupal node, and then I perform that test:

Scala: How to extract parts of a String that match regex patterns

This is an excerpt from the Scala Cookbook (partially modified for the internet). This is Recipe 1.9, “Extracting Parts of a String that Match Patterns.”

Problem

You want to extract one or more parts of a Scala String that match the regular-expression patterns you specify.

Solution

Define the regular-expression (regex) patterns you want to extract, placing parentheses around them so you can extract them as “regular-expression groups.” First, define the desired pattern:

How to find regex patterns in Scala strings

This is an excerpt from the Scala Cookbook (partially modified for the internet). This is Recipe 1.7, “Finding Patterns in Scala Strings.”

Problem

You need to determine whether a Scala String contains a regular expression pattern.

This is a page from my book, Functional Programming, Simplified

How to Write Scala Functions That Take Functions as Input Parameters

“Haskell functions can take functions as parameters and return functions as return values. A function that does either of those is called a higher order function. Higher order functions aren’t just a part of the Haskell experience, they pretty much are the Haskell experience.”

From Learn You a Haskell for Great Good