Meta Character in Linux

In this tutorial, we’ll cover the most common meta characters used in Linux commands and how to use them.

Meta Character in Linux

1. Asterisk (*)

The asterisk (*) is the most commonly used meta character in Linux commands. It represents zero or more characters in a filename. For example, if you want to list all files in a directory that end with the “.txt” extension, you can use the following command:

ls *.txt

This will list all files in the current directory that end with the “.txt” extension.

2. Question mark (?)

The question mark (?) represents a single character in a filename. For example, if you want to “list any file that have a three-letter as name before the filename extension, you can use the following command:

ls ???.*

This will list all files in the current directory that have a three-letter that have a three-letter as name.

3. Brackets ([ ])

Brackets ([…]) are used to match a set of specified characters. A comma separates each character within the set. Typing the following will list all files beginning with “a”, “b”, or “c”:

$ ls [a,b,c]*

4. The Hyphen

Using the – (hyphen) metacharacter within [] (brackets) is used to match a specified range of characters. Typing the following will list all files beginning with a lowercase letter of the alphabet:

$ ls [a-z]*

5. Brace expansion ({ })

Brace expansion ({ }) is used to generate multiple strings from a pattern. For example, if you want to create multiple directories with similar names, you can use the following command:

mkdir {dir1,dir2,dir3}

This will create three directories named “dir1”, “dir2”, and “dir3”.

6. Tilde (~)

The tilde (~) is used to represent the home directory of the current user. For example, if you want to navigate to your home directory, you can use the following command:

cd ~

This will take you to your home directory.

7. Period (.)

The period (.) is used to represent the current directory. For example, if you want to list all files in the current directory, you can use the following command:

ls .

This will list all files in the current directory.

8. $ (Dollar)

The dollar sign is used to access the value of a shell variable. For example, if you have set a variable called “myvar” to the value “hello”, you can use the command:

$ echo $myvar

This will display the value of the variable “myvar”, which is “hello”.

9. & (Ampersand)

The ampersand is used to run a command in the background. For example, if you want to run a command called “mycommand” in the background, you can use the command:

$ mycommand &

This will run the command “mycommand” in the background, allowing you to continue working in the shell.

10. Pipes

Pipes are used to connect the output of one command to the input of another command. The pipe character is represented by the ‘|’ symbol. For example, to list all the files in the current directory and then sort the output in alphabetical order, you can use the following command:

ls | sort

This will send the output of the ‘ls’ command to the ‘sort’ command and sort the results.

11. Redirection

Redirection is used to redirect the output of a command to a file or another command. The following are the commonly used redirection operators:

• > – Redirects the output of a command to a file, overwriting the existing content of the file.
• >> – Redirects the output of a command to a file, appending the output to the existing content of the file.
• < – Redirects the input of a command from a file.

For example, to redirect the output of the ls command to a file named filelist.txt, you can use the following command:

$ ls > filelist.txt

In conclusion, meta characters are an essential part of the Linux command line. They provide a powerful mechanism to perform various operations on files and directories. By understanding how to use these meta characters, you can become more efficient in your work and automate repetitive tasks.