Shell learning: About replacement commands-tr-ROT13 rules

[Root @ stu100 ~] # Echo abcdef | tr abcdef xyzabc

Xyzabc

[Root @ stu100 ~] # Echo abcdef | tr a-f x-za-c

Xyzabc

The following example demonstrates a popular method of hiding text. Because the first character of the alphabet is replaced with 13th characters, the first character is replaced with 2nd characters, and so on, therefore, it is usually called ROT13 (rotate 13)

[Root @ stu100 ~] # Echo the punchline of the joke is... | tr A-M N-Z a-m n-z N-Z n-z a-m

Gur chapuyvar bs gur wbxr vf...

To make the hidden text readable, you can achieve this by exchanging the tr parameter:

[Root @ stu100 ~] # Echo gur chapuyvar bs gur wbxr vf... | tr N-Z A-M n-z a-m A-M N-Z a-m n-z

The punchline of the joke is...

In the following example, tr first replaces the character, and then replaces several pairs of identical characters with a single character:

[Root @ stu100 ~] # Echo tennessee | tr-s tnse srne

Serene

This is the legendary ROT13 rule.