What is character class in bash shell linux and how to use them to search a pattern ?
In Linux, Character Classes is a group of characters which are responsible to perform pattern matching.
Character Classes are defined using “[]” i.e. square brackets and matches any of the mentioned patterns.
I. Few examples of Character Class
Any character --> "." dot special character. All lower case alphabets --> [a-z] Upper case alphabets --> [A-Z] Match lower and upper case character "e" --> [eE] And so on......
II. How to use character class ?
### Create a text file below.
ngelinux saket$ cat testfile
Welcome to NGELinux.
This is a sample file.
Here we will see chracter class example.
It works on ArchLinux, and other Linux versions also.
ngelinux saket$
### Example 1: Match any of the "eEhHL"Linux pattern.
$ awk '/[eEhHL]inux/{print $0}' testfile
Welcome to NGELinux.
It works on ArchLinux, and other Linux versions also.
ngelinux saket$
### Example 2: Look for lower case w character.
$ awk '/[w]/{print $0}' testfile
Here we will see chracter class example.
It works on ArchLinux, and other Linux versions also.
### Example 3: Look for either lowercase or uppercase character w.
$ awk '/[wW]/{print $0}' testfile
Welcome to NGELinux.
Here we will see chracter class example.
It works on ArchLinux, and other Linux versions also.
In a similar fashion above, we can make any set of character class and do the pattern matching as per our convenience.