Dot

The "." character is one of those special metacharacters that matches any character, except the end-of-line character. In the following example, we match a sequence of three characters that begin with C and end with T, as follows:

$ echo -e "C1T\nCaT\nC@T\ncAT" | awk '/C.T/ { print }'

The output on execution of the preceding program is as follows:

C1T
CaT
C@T

Let's create one file for practicing dot regular expressions:

$ vi dot_regex.txt 
Lets go for a walk
Singing is good hobby
We will talk on this matter
Ping me when you are free
(that is cool)
My son birthday is on 24/04/14
I will be going to Singapore on 24-04-14
(this)

Now, let's execute some regular expressions on the dot_regex.txt file:

1. Match all strings with any character preceded by 'ing', as follows:

$ awk '/.ing/{ print }'  dot_regex.txt

The output on execution of this code is:

Singing is good hobby
Ping me when you are free
I will be going to Singapore on  24-04-14

2. Match all strings that contain a space, followed by a character, and further followed by 'alk':

$ awk '/ .alk/{ print }'  dot_regex.txt

The output on execution of the preceding code is as follows:

Lets go for a walk
We will talk on this matter

3. Match the date with any separator, as follows:

$ awk '/24.04.14/{ print }' dot_regex.txt

The output on execution of the given code is as follows:

My son birthday is on 24/04/14
I will be going to Singapore on  24-04-14

A summary of dot/period is as follows: