Beginners guide for Regular Expressions(regexp)

Top 10 basic regexp to know for Ansible beginners while using "replace" or "lineinfile" modules

1. Start with Special character.

(dot) .

It selects all the content, expect new lines. example

2. To avoid and just want to select the literal character of (Dot). then use literal MetaCharacter as below

(back slash) \

3. When we want to select the exact word, as it is case senstive.

ex:  try with "case sentive" vs "Case Sensitive" 

4.  When there is a repetition of the same word, but we need to select the word or character that begins the line.
     Beginning of a string - "^
 ex:  ^

5.  When we want to filter more specific word that starts with and end with.
     Use Anchors "^" - Beginning of String and "$" - End of String
     The below example has in two places but we need a specific one that starts at beginning of a line.
ex: ^$

6.  Select a specific word that has a boundary.
      ex: "GODOFFIRE Prometheus"  and "GODOFFIREPrometheus" 
when we just filter the word Prometheus, it will select all the matching words with or without boundaries. using "\bPrometheus" filter matches that have a Boundary as shown below. 

7. Opposite to the above selection, the word that should not have a Boundary.

8.  At times we want to filter numbers that matches certain pattern.
     ex: Let's assume we have a 10 digit phone number, but it has no standard format and now we want to filter all the match cases. 
"\d" "{}-quantifier" "dot(.) - selects any"  

9. when we want to filter the exact literal match of a standard format along with specific starting area codes. 
ex: 55* 66* 56* 65* - we can write as [56][65] as starting two numbers.
we can use character set [ ]

10.  At times we have to filter and replace a combo of a few characters or words which has both numbers, special characters, and letters(including upper and lower cases)
ex: replace all the websites, emails, servernames etc with company proxy server.
we can use groups"()" and quantifiers"[]" to acheive this.


Exact realtime Ansible examples will be coming in next slide.


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