Overview

Dot ‘.’ character is one of the most commonly used metacharacters in the regular expression. It is used to match any character. By default, it doesn’t match a new line.

Now let’s see a simple program for Dot ‘.’ character

Program

match = "a".match(/./)
puts "For a: " + match.to_s

match = "b".match(/./)
puts "For b: " +  match.to_s

match = "ab".match(/./)
puts "For ab: " +  match.to_s

match = "".match(/./)
puts "For Empty String: " +  match.to_s

Output

For a: a
For b: b
For ab: a
For Empty String:

In the above program, we have a simple regex containing only one dot character.

/./

It matches below characters and string.

a
b
ab

It matches ab because by default the regex doesn’t do the match the full string unless we use the anchor characters (Caret and Dollar character). That is why it matches the first character ‘a’ in ‘ab’ and reports a match.It doesn’t match an empty string.

Let’s see another example where we have two dots in the regex.

match = "ab".match(/../)
puts "For ab: " + match.to_s

match = "ba".match(/../)
puts "For ba: " + match.to_s

match = "abc".match(/../)
puts "For abc: " + match.to_s

match = "a".match(/../)
puts "For a: " + match.to_s

Output

For ab: ab
For ba: ba
For abc: ab
For a:

In the above program, we have a simple regex containing two dots.

/../

It will match any given string which has at least two characters as a substring.

That is why it gives a match for

ab
ba
abc

and doesn’t give a match for (It gives an empty string match)