Scripting

Catching Errors in sed Detecting errors is the first step towards handling them gracefully in sed scripts. The exit code of the last command executed is stored in the $? variable. Checking this variable after running sed allows detecting errors via non-zero exit codes. Using Exit Codes to Detect Errors A simple way to check…

Understanding In-Place Editing In-place editing refers to modifying a file directly on disk, rather than creating a separate output file with the changes. The sed utility allows performing fast in-place edits on text files using regular expressions and editing commands. Typical use cases where in-place editing with sed excels include: Mass find-and-replace operations across multiple…

Why Escaping Characters Matters in sed The sed text processing utility interprets certain characters in a special way during its substitution commands. Characters like the forward slash (/), backslash (\), and dollar sign ($) have predefined functions in the syntax of sed substitution, so they need to be escaped if you want them to be…

Understanding Argument Parsing in Bash In Bash scripts, arguments refer to the data passed to commands, programs, functions, and scripts. Understanding how Bash handles argument parsing is crucial for writing robust scripts that accept input correctly. There are two main types of arguments in Bash: Positional Arguments – Arguments that are mapped to variables based…

The Challenges of Parsing Raw argv Input Command line programs often need to accept input options to customize their behavior. However, directly parsing the raw argv array received by main() can be challenging. The position and order of options may vary, optional arguments may or may not be present, and additional validation code is needed…

Ensuring Reliable Input with Bash Read The Bash read command allows input from the user to be assigned to variables for later use in scripts and programs. However, care must be taken to properly validate and sanitize this input before relying on it for critical operations. Why Validate User Input User input from the Bash…

Failing to Properly Quote Variables One of the most common pitfalls when assigning command output to a variable in Bash is failing to properly quote the variable expansion. When you assign output to a variable without quoting, like this: out=$(mycommand) Bash will perform word splitting and filename expansion on the unquoted variable, which can lead…

When to Prefer $(…) Over Backticks The $(…) syntax for command substitution, also known as the dollar-paren syntax, has several advantages over using backticks “: $(…) substitutions are more readable and less visually cluttered in most cases Nested substitutions and quoting work better with $(…) compared to backticks The $(…) style is supported in all…

Getting Started with Command Substitution Definition and Basic Syntax of Command Substitution in Bash Command substitution in Bash allows you to assign the output of a command to a variable or pass it as an argument to another command. It substitutes the command with its output. The basic syntax for command substitution is: $(command) `command`…

Why Man Pages Matter Man pages serve as the primary documentation for programs and scripts on Linux and Unix-based systems. They provide essential reference information that enables users to understand and effectively utilize commands and applications. Man pages are vital for ensuring the usability of custom scripts and software in several key ways: Providing essential…