Wildcards Spare tricks

👉 Overview

👀 What ?

Linux Wildcards are symbols that enable users to select filenames based on patterns of characters. The wildcard characters in Linux are * (asterisk), ? (question mark), and [ ] (brackets). The * wildcard represents any number of characters, including none, while the ? wildcard represents only one character. Brackets are used to specify a range of characters.

🧐 Why ?

Understanding and using Linux wildcards is important because they provide a powerful tool for managing files efficiently. They can simplify tasks by reducing the need to enter long filenames, help in file searching, and allow for quick and efficient file management. The use of wildcards can significantly improve the productivity and efficiency of working with Linux systems.

⛏️ How ?

Using Linux wildcards is quite straightforward. For instance, to list all files that end with .txt, you would use the command 'ls .txt'. To list all files that start with a and end with .txt, use 'ls a.txt'. To list all files that have exactly two characters in their names, use 'ls ??'. To list all files that start with a or b, use 'ls [ab]*'.

⏳ When ?

The use of wildcards in Linux started since the early development of Unix-like operating systems, where they were incorporated into the design of the shell to provide users with flexible file management capabilities.

⚙️ Technical Explanations

In Linux, wildcards are special characters that help users perform operations on multiple files simultaneously, making file management more efficient. The process by which these wildcards get interpreted is known as 'globbing'. Here's a deeper look into it:

When a command involving a wildcard is entered, the shell (the program that interprets command line instructions) first identifies any wildcard present. It then expands this wildcard into a list of filenames that match the pattern specified by the wildcard.

For example, if a user types 'ls .txt', the shell sees the '' wildcard and understands it to represent any possible characters. So, it expands '*.txt' into a list of all filenames in the current directory that end with '.txt'. The 'ls' command is then run on this list of filenames.

It's important to note that the command itself (in this case, 'ls') doesn't know that a wildcard was used. All it sees are the filenames that the shell presents to it after expanding the wildcard. This is because the shell processes the wildcard before the command is executed.

In a case where a wildcard pattern doesn't match any filenames, the command is run with the literal wildcard pattern. For example, if there are no '.txt' files in the directory and the user types 'ls .txt', the 'ls' command will look for a file literally named '.txt', and not finding any, will return an error message.

Understanding and effectively using wildcards can significantly boost productivity and efficiency when working with Linux systems, as it allows for simplified and flexible file management.

Let's walk through a detailed example of using Linux wildcards:

1. Suppose we have a directory of text files named file1.txt, file2.txt, file3.txt, and an image file image1.png.
2. To list all the text files, we can use the ls command with the wildcard .txt.

ls *.txt

The * wildcard represents any number of characters, so *.txt would match any filename that ends with .txt. The command will list file1.txt, file2.txt, file3.txt.

1. To list files starting with 'file' followed by any one character, we can use ? wildcard.

ls file?.txt

The ? wildcard represents exactly one character, so file?.txt would match any filename that starts with 'file', followed by any one character, and ends with .txt. The command will list file1.txt, file2.txt, file3.txt.

1. If we want to list files that start with 'file1' or 'file2', we can use the [ ] wildcard.

ls file[12].txt

The [12] wildcard represents either '1' or '2', so file[12].txt would match any filename that starts with 'file', followed by '1' or '2', and ends with .txt. The command will list file1.txt, file2.txt.

1. If there are no matches for the wildcard pattern, the command is run with the literal wildcard pattern. For example, if we run:

ls file4.txt

Since there is no file4.txt in the directory, the ls command will look for a file literally named 'file4.txt' and not finding any, it will return an error message: ls: cannot access 'file4.txt': No such file or directory.

These examples illustrate how Linux wildcards can be used to perform operations on multiple files simultaneously, simplifying file management.