Linux

The diff command is an easy way to compare files or directories from the Linux shell. This article will show you how to use it, with some examples of common usage. The diff command performs a line-by-line comparison of two files or directories and outputs the differences between them. Why would you want to compare files or directories? You might have two files with the same name that look similar and want to see the difference between them. Comparing changes to the programming code in a project you’re … Read more

The cat (concatenate) command in Linux/Bash is most commonly used to read the contents of a file. It outputs the contents of a given file. Here’s how to use it. cat concatenates files to standard output – by default, this is to the console for viewing on your computer screen. This makes it useful for quickly viewing the contents of files. It also has other uses, but first, the syntax: cat Syntax cat [OPTIONS] [FILE] Note that: If FILE is not specified, will read from standard input (stdin) Multiple FILEs can be specified, separated by … Read more

The Linux/Bash shell has three data streams that you can tap into when executing commands – stdin, stdout, and stderr. Here’s how to use them. stdin, stdout, stderr allow for the display of text in the console, and the data being output each stream can be directed into other programs. These are referred to as Standard Streams. What is stdin (Standard Input)? Text input stream. Applications can accept text via stdin as input. What is stdout (Standard Output)? The text output stream of a program. Applications send data to other programs (or to the console for viewing) via stdout. … Read more

Here’s a short article on concatenating (merging) strings in Bash – the right way. Examples included. There are various ways two or more strings could be joined in a shell script. Various programs will accept strings and return them merged/concatenated – but using the side-effect of a programs operation to concatenate strings is a bit of a waste of time, so this article will focus on the simplest, most readable method. Inserting a String into Another A string can be inserted when creating another string … Read more

Math is easy, Bash scripting is easy, so performing math/arithmetic in Bash/Shell scripts should be easy too. It is. Here’s how to do it. Working with Integers Bash’s built-in arithmetic can only handle integer (whole number) values. If you attempt to declare a variable with a non-integer value: declare -i e=2.5 You’ll see the following: bash: declare: 2.5: syntax error: invalid arithmetic operator (error token is “.5”) To work with non-integer numbers, you will need to use an external program to perform your calculations – but first, … Read more